エアロゾル気候モデルの開発とその気候変動および黄砂・PM2.5分布予測などの大気環境研究への適用

エアロゾルの気候影響に関するモデル研究

Outstanding contributions to the field and pioneering works on aerosol-cloud-climate interactions and the atmospheric aerosol modeling

エアロゾルの気候影響評価のためのシミュレーションモデルの開発

Development of global aerosol transport-radiation model

全球３次元エアロゾル輸送・放射モデルを用いたエアロゾルの分布及び放射強制に関する研究

Language：English   Publishing type：Research paper (scientific journal)  

The aerosol semi-direct effect is generally explained as follows: aerosols, such as black carbon (BC) and mineral dust, absorb solar radiation, which warms and stabilizes the atmosphere, resulting in reduced cloudiness and cloud formation. However, the present study suggests that BC can intensify atmospheric instability and thus increase cloud water and precipitation if the BC is concentrated near the surface. Simulations using a global aerosol climate model, based on a general circulation model, show decreased cloud water over biomass-burning regions where BC is emitted to the free troposphere through the boundary layer. In contrast, increased cloud water is indicated over East and South Asia where BC from urban and industrial activities is concentrated near the surface. While the global mean change in the radiation budget at the top of the atmosphere due to the semi-direct effect of BC is estimated to be as small as +0.06 W m(-2), regional changes in cloud water, precipitation, and shortwave radiation are suggested to be large enough to modify meteorological conditions in urban and biomass-burning regions.

DOI： 10.2151/sola.2011-046

Other Link： https://www.jstage.jst.go.jp/article/sola/7/0/7_0_181/_article

Language：English   Publishing type：Research paper (scientific journal)  

The powerful tsunami generated by the massive earthquake that occurred east of Japan on March 11, 2011 caused serious damages of the Fukushima Daiichi Nuclear Power Plant on its cooling facilities for nuclear reactors. Hydrogen and vapor blasts that occurred until March 15 outside of the reactors led to the emission of radioactive materials into the air. Here we show a numerical simulation for the long-range transport from the plant to the U. S. and even Europe with a global aerosol transport model SPRINTARS. Large-scale updraft organized by a low-pressure system traveling across Japan from March 14 to 15 was found effective in lifting the particles from the surface layer to the level of a westerly jet stream that could carry the particles across the Pacific within 3 to 4 days. Their simulated concentration rapidly decreases to the order of 10(-8) of its initial level, consistent with the level detected in California on March 18. The simulation also reproduces the subsequent trans-Atlantic transport of those particles by a poleward-deflected jet stream, first toward Iceland and then southward to continental Europe as actually observed.

DOI： 10.2151/sola.2011-026

Other Link： https://www.jstage.jst.go.jp/article/sola/7/0/7_0_101/_article

Language：English   Publishing type：Research paper (scientific journal)  

In this study an integrated simulation of the global distribution and the radiative forcing of soil dust aerosols at the Last Glacial Maximum (LGM) is performed with an aerosol climate model, SPRINTARS. It is compared with another simulation for the present climate condition. The global total emission flux of soil dust aerosols at the LGM is simulated to be about 2.4 times as large as that in the present climate, and the simulated deposition flux is in general agreement with estimations from ice core and marine sediment samplings though it appears to be underestimated over the Antarctic. The calculated direct radiative forcings of soil dust aerosols at the LGM is close to zero at the tropopause and -0.4 W m(-2) at the surface. These radiative forcings are about twice as large as those in the present climate. SPRINTARS also includes the microphysical parameterizations of the cloud-aerosol interaction both for liquid water and ice crystals, which affect the radiation budget. The positive radiative forcing from the indirect effect of soil dust aerosols is mainly caused by their properties to act as ice nuclei. This effect is simulated to be smaller (-0.9 W m(-2)) at the LGM than in the present. It is suggested that atmospheric dust might contribute to the cold climate during the glacial periods both through the direct and indirect effects, relative to the interglacial periods.

DOI： 10.5194/acp-9-3061-2009

Other Link： http://www.atmos-chem-phys.net/9/3061/2009/acp-9-3061-2009.html

Language：English   Publishing type：Research paper (scientific journal)  

Aerosols may influence cloud formation through two pathways: One is the effect on cloud microphysics by forming smaller and more numerous cloud droplets reducing precipitation and consequently enhancing cloud lifetime. The second is referred to as the aerosol dynamic-hydrological effect in which the aerosol direct, semi-direct, and indirect effects can modulate atmospheric radiation, which perturbs atmospheric circulation, leading to redistributions of clouds and precipitation. Here this study examines climate sensitivities using a general circulation model coupled with an aerosol transport-radiation model. The model is run first with prescribed meteorology in order to isolate the cloud microphysical effect. It is run in a separate experiment with internally generated meteorology that includes dynamic-hydrological effect as the aerosols modify clouds and interact with the radiation. We find in some regions that the dynamic-hydrological effect in the free model runs counteracts the microphysical effects seen in the prescribed runs.

DOI： 10.1029/2006GL028349

Other Link： http://dx.doi.org/10.1029/2006GL028349

Language：English   Publishing type：Research paper (scientific journal)  

Time series of the instantaneous radiative forcings for main anthropogenic and natural forcing agents from the year 1850 to 2000 are evaluated at the Earth's surface as well as at the tropopause with an atmospheric general circulation model. This evaluation corresponds to a simulation of 20th century climate with a synthetic coupled atmosphere-ocean general circulation model. The evaluation indicates that the positive radiative forcing at the tropopause rapidly increases from 1910 to 1950 and after 1970 principally due to long-lived greenhouse gases, while the negative radiative forcing at the surface sharply increases between 1955 and 1965 mainly due to the aerosol direct and indirect effects. This study suggests that a simultaneous analysis of changing rates of the radiative forcing both at the tropopause and surface can explain tendencies of changes in the surface air temperature.

DOI： 10.1029/2006GL026666

Other Link： http://dx.doi.org/10.1029/2006GL026666

Language：English   Publishing type：Research paper (scientific journal)  

[ 1] With a global aerosol transport-radiation model coupled to a general circulation model, changes in the meteorological parameters of clouds, precipitation, and temperature caused by the direct and indirect effects of aerosols are simulated, and its radiative forcing are calculated. A microphysical parameterization diagnosing the cloud droplet number concentration based on the Kohler theory is introduced into the model, which depends not only on the aerosol particle number concentration but also on the updraft velocity, size distributions, and chemical properties of each aerosol species and saturation condition of the water vapor. The simulated cloud droplet effective radius, cloud radiative forcing, and precipitation rate, which relate to the aerosol indirect effect, are in reasonable agreement with satellite observations. The model results indicate that a decrease in the cloud droplet effective radius by anthropogenic aerosols occurs globally, while changes in the cloud water and precipitation are strongly affected by a variation of the dynamical hydrological cycle with a temperature change by the aerosol direct and first indirect effects rather than the second indirect effect itself. However, the cloud water can increase and the precipitation can simultaneously decrease in regions where a large amount of anthropogenic aerosols and cloud water exist, which is a strong signal of the second indirect effect. The global mean radiative forcings of the direct and indirect effects at the tropopause by anthropogenic aerosols are calculated to be -0.1 and -0.9 W m(-2), respectively. It is suggested that aerosol particles approximately reduce 40% of the increase in the surface air temperature by anthropogenic greenhouse gases on the global mean.

DOI： 10.1029/2004JD005029

Other Link： http://dx.doi.org/10.1029/2004JD005029

Language：English   Publishing type：Research paper (scientific journal)  

A three-dimensional aerosol transport-radiation model coupled with a general circulation model, Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS), simulates atmospheric aerosol distributions and optical properties. The simulated results are compared with aerosol sampling and optical observations from ground, aircraft, and satellite acquired by intensive observation campaigns over east Asia in spring 2001. Temporal variations of the aerosol concentrations, optical thickness, and Angstrom exponent are in good agreement between the simulation and observations. The midrange values of the Angstrom exponent, even at the Asian dust storm events over the outflow regions, suggest that the contribution of the anthropogenic aerosol, such as carbonaceous and sulfate, to the total optical thickness is of an order comparable to that of the Asian dust. The radiative forcing by the aerosol direct and indirect effects is also calculated. The negative direct radiative forcing is simulated to be over -10 W m(-2) at the tropopause in the air mass during the large-scale dust storm, to which both anthropogenic aerosols and Asian dust contribute almost equivalently. The direct radiative forcing, however, largely depends on the cloud water content and the vertical profiles of aerosol and cloud. The simulation shows that not only sulfate and sea salt aerosols but also black carbon and soil dust aerosols, which absorb solar and thermal radiation, make strong negative radiative forcing by the direct effect at the surface, which may exceed the positive forcing by anthropogenic greenhouse gases over the east Asian region.

DOI： 10.1029/2002JD003210

Other Link： http://dx.doi.org/10.1029/2002JD003210

Language：English   Publishing type：Research paper (scientific journal)  

[1] A three-dimensional aerosol transport-radiation model, SPRINTARS, successfully simulates the long-range transport of the large-scale Asian dust storms from East Asia to North America which crossed the North Pacific Ocean during the springtime of 2001 and 2002. It is found from the calculated dust optical thickness that 10 to 20% of the Asian dust around Japan reached North America. The simulation also reveals the importance of the contribution of anthropogenic aerosols, which are carbonaceous and sulfate aerosols emitted from the industrialized areas in East Asia, to air turbidity during the dust storms. The contribution of the anthropogenic aerosol to the total optical thickness is simulated to be of a comparable order to that of the Asian dust, which is consistent with the observed values of the particle size index from the satellite and ground-based sun/sky photometry.

DOI： 10.1029/2002GL016251

Other Link： http://dx.doi.org/10.1029/2002GL016251

Language：English   Publishing type：Research paper (scientific journal)  

Global distributions of the aerosol optical thickness, Angstromngstrom exponent, and single-scattering albedo are simulated using an aerosol transport model coupled with an atmospheric general circulation model. All the main tropospheric aerosols are treated, that is, carbonaceous (organic and black carbons), sulfate, soil dust, and sea salt aerosols. The simulated total aerosol optical thickness, Angstromngstrom exponent, and single-scattering albedo for mixtures of four aerosol species are compared with observed values from both optical ground-based measurements and satellite remote sensing retrievals at dozens of locations including seasonal variations. The mean difference between the simulation and observations is found to be less than 30% for the optical thickness and less than 0.05 for the single-scattering albedo in most regions. The simulated single-scattering albedo over the Saharan region is, however, substantially smaller than the observation, though the standard optical constant of soil dust is used in this study. The radiative forcing by the direct effect of the main tropospheric aerosols is then estimated. The global annual mean values of the total direct radiative forcing of anthropogenic carbonaceous plus sulfate aerosols are calculated to be -0.19 and -0.75 W m(-2) under whole-sky and clear-sky conditions at the tropopause, respectively.

DOI： 10.1175/1520-0442(2002)015<0333:SSAARF>2.0.CO;2

Other Link： http://ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2F1520-0442%282002%29015%3C0333%3ASSAARF%3E2.0.CO%3B2

Language：English   Publishing type：Research paper (scientific journal)  

Distributions of aerosol concentrations, optical properties, and wet deposition fluxes are simulated for the next fifty years using an aerosol transport model coupled with an atmospheric general circulation model. Treated species are sulfur dioxide, and all the main tropospheric aerosols, i.e., carbonaceous (black and organic carbons), sulfate, soil dust, and sea salt. We especially pay attention to distributions of anthropogenic carbonaceous aerosols, sulfate aerosols, and sulfur dioxide. The simulation uses the Special Report on Emissions Scenarios (SRES) of the Intergovernmental Panel on Climate Change (IPCC) as the future emission scenarios of anthropogenic pollutants. Simulated results suggest that carbonaceous aerosols continue to increase over industrial and densely populated regions for the next five decades, whereas sulfate aerosols decrease around Europe and North America. The aerosol single scattering albedo in the future is, therefore, calculated to become small gradually in the mid- and high-latitudes of the Northern Hemisphere. Sulfate aerosols and sulfur wet deposition fluxes are, on the other hand, simulated to increase only over East Asia. Black carbon and sulfate aerosols around Japan in 2050 are simulated to be two or three times as large as those in 2000 with one of the SIZES scenarios. Hence this suggests that pollutants originating from the East Asian continent can seriously affect the atmospheric quality in Japan in the next several decades.

DOI： 10.2151/jmsj.79.1139

Other Link： https://www.jstage.jst.go.jp/article/jmsj/79/6/79_6_1139/_article

Language：English   Publishing type：Research paper (scientific journal)  

A global three-dimensional model that can treat transportation of various species of aerosols in the atmosphere is developed using a framework of an atmospheric general circulation model (AGCM). Main aerosols in the troposphere, i.e., soil dust, carbonaceous (organic and black carbon), sulfate, and sea-salt aerosols, are introduced into this model. Prior to the model calculations the meteorological parameters are calculated by the AGCM with the nudging technique using reanalysis data. To evaluate aerosol effects on the climate system and to compare simulated results with observations, the optical thickness and Angstrom exponent are also calculated taking into account the size distribution and composition. The model results are validated by both measured surface aerosol concentrations and retrieved aerosol optical parameters from National Oceanic and Atmospheric Administration/Advanced Very High Resolution Radiometer. A general agreement is found between the simulated result and the observation globally and seasonally. One of the significant results is that the simulated relative contribution of anthropogenic carbonaceous aerosols to the total optical thickness is comparable to that of sulfate aerosols at midlatitudes of the Northern Hemisphere, which agrees with recent observations. This result leads to a conclusion that the radiative effect evaluation of aerosols on the climate system is necessary to be modified because optical properties of carbonaceous aerosols are different from those of sulfate aerosols. The other finding is that the seasonal shift off the west coast of North Africa observed by satellites, i.e., the latitude of the maximum optical thickness moves seasonally, is also reproduced in consideration of a mixed state of soil dust and carbonaceous aerosols. Copyright 2000 by the American Geophysical Union.

DOI： 10.1029/2000JD900265

Other Link： http://dx.doi.org/10.1029/2000JD900265

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.envres.2024.118292

Language：Others  

The climate science community aims to improve our understanding of climate change due to anthropogenic influences on atmospheric composition and the Earth's surface. Yet not all climate interactions are fully understood, and uncertainty in climate model results persists, as assessed in the latest Intergovernmental Panel on Climate Change (IPCC) assessment report. We synthesize current challenges and emphasize opportunities for advancing our understanding of the interactions between atmospheric composition, air quality, and climate change, as well as for quantifying model diversity. Our perspective is based on expert views from three multi-model intercomparison projects (MIPs) - the Precipitation Driver Response MIP (PDRMIP), the Aerosol Chemistry MIP (AerChemMIP), and the Radiative Forcing MIP (RFMIP). While there are many shared interests and specializations across the MIPs, they have their own scientific foci and specific approaches. The partial overlap between the MIPs proved useful for advancing the understanding of the perturbation-response paradigm through multi-model ensembles of Earth system models of varying complexity. We discuss the challenges of gaining insights from Earth system models that face computational and process representation limits and provide guidance from our lessons learned. Promising i

DOI： 10.5194/gmd-17-2387-2024

Language：Others   Publishing type：Research paper (scientific journal)  

For over 6 months, the 2014-2015 effusive eruption at Holuhraun, Iceland, injected considerable amounts of sulfur dioxide (SO2) into the lower troposphere with a daily rate of up to one-third of the global emission rate, causing extensive air pollution across Europe. The large injection of SO2, which oxidises to form sulfate aerosol (SO42-), provides a natural experiment offering an ideal opportunity to scrutinise state-of-the-art general circulation models' (GCMs) representation of aerosol-cloud interactions (ACIs). Here we present Part 1 of a two-part model inter-comparison using the Holuhraun eruption as a framework to analyse ACIs. We use SO2 retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) instrument and ground-based measurements of SO2 and SO42- mass concentrations across Europe, in conjunction with a trajectory analysis using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model, to assess the spatial and chemical evolution of the volcanic plume as simulated by five GCMs and a chemical transport model (CTM). IASI retrievals of plume altitude and SO2 column load reveal that the volcanic perturbation is largely contained within the lower troposphere. Compared to the satellite observations, the models capture the spatial evolution and vertical variability of the plume reasonably well, although the models often overestimate the plume altitude. HYSPLIT trajectories are used to attribute to Holuhraun emissions 111 instances of elevated sulfurous surface mass concentrations recorded at European Monitoring and Evaluation Programme (EMEP) stations during September and October 2014. Comparisons with the simulated concentrations show that the modelled ratio of SO2 to SO42- during these pollution episodes is often underestimated and overestimated for the young and mature plume, respectively. Models with finer vertical resolutions near the surface are found to better capture these elevated sulfurous ground-level concentrations. Using an exponential function to describe the decay of observed surface mass concentration ratios of SO2 to SO42- with plume age, the in-plume oxidation rate constant is estimated as 0.032±0.002h-1 (1.30±0.08d e-folding time), with a near-vent ratio of 25±5 (μgm-3 of SO2/μgm-3 of SO42-). The majority of the corresponding derived modelled oxidation rate constants are lower than the observed estimate. This suggests that the representation of the oxidation pathway/s in the simulated plumes is too slow. Overall, despite their coarse spatial resolutions, the six models show reasonable skill in capturing the spatial and chemical evolution of the Holuhraun plume. This capable representation of the underlying aerosol perturbation is essential to enable the investigation of the eruption's impact on ACIs in the second part of this study.

DOI： 10.5194/acp-24-1939-2024

Language：Others   Publishing type：Research paper (scientific journal)  

In accordance with progression in current capabilities towards high-resolution approaches, applying a convective-permitting resolution to global aerosol models helps comprehend how complex cloud-precipitation systems interact with aerosols. This study investigates the impacts of a double-moment bulk cloud microphysics scheme, i.e., NICAM Double-moment bulk Water 6 developed in this study (NDW6-G23), on the spatiotemporal distribution of aerosols in the Nonhydrostatic ICosahedral Atmospheric Model as part of the version-19 series (NICAM.19) with 14gkm grid spacing. The mass concentrations and optical thickness of the NICAM-simulated aerosols are generally comparable to those obtained from in situ measurements. However, for some aerosol species, especially dust and sulfate, the differences between experiments of NDW6 and of the NICAM single-moment bulk module with six water categories (NSW6) were larger than those between experiments with different horizontal resolutions (14 and 56gkm grid spacing), as shown in a previous study. The simulated aerosol burdens using NDW6 are generally lower than those using NSW6; the net instantaneous radiative forcing due to aerosol-radiation interaction (IRFari) is estimated to be-1.36gWgm-2 (NDW6) and-1.62gWgm-2 (NSW6) in the global annual mean values at the top of the atmosphere (TOA). The net effective radiative forcing due to anthropogenic aerosol-radiation interaction (ERFari) is estimated to be-0.19gWgm-2 (NDW6) and-0.23gWgm-2 (NSW6) in the global annual mean values at the TOA. This difference among the experiments using different cloud microphysics modules, i.e., 0.26gWgm-2 or 16g% difference in IRFari values and 0.04gWgm-2 or 16g% difference in ERFari values, is attributed to a different ratio of column precipitation to the sum of the column precipitation and column liquid cloud water, which strongly determines the magnitude of wet deposition in the simulated aerosols. Since the simulated ratios in the NDW6 experiment are larger than those of the NSW6 result, the scavenging effect of the simulated aerosols in the NDW6 experiment is larger than that in the NSW6 experiment. A large difference between the experiments is also found in the aerosol indirect effect (AIE), i.e., the net effective radiative forcing due to aerosol-cloud interaction (ERFaci) from the present to preindustrial days, which is estimated to be-1.28gWgm-2 (NDW6) and-0.73gWgm-2 (NSW6) in global annual mean values. The magnitude of the ERFaci value in the NDW6 experiment is larger than that in the NSW6 result due to the differences in both the Twomey effect and the susceptibility of the simulated cloud water to the simulated aerosols between NDW6 and NSW6. Therefore, this study shows the importance of the impacts of the cloud microphysics module on aerosol distributions through both aerosol wet deposition and the AIE.

DOI： 10.5194/gmd-17-651-2024

Language：Others   Publishing type：Research paper (scientific journal)  

Absorbing aerosols emitted from biomass burning (BB) greatly affect the radiation balance, cloudiness, and circulation over tropical regions. Assessments of these impacts rely heavily on the modeled aerosol absorption from poorly constrained global models and thus exhibit large uncertainties. By combining the AeroCom model ensemble with satellite and in situ observations, we provide constraints on the aerosol absorption optical depth (AAOD) over the Amazon and Africa. Our approach enables identification of error contributions from emission, lifetime, and MAC (mass absorption coefficient) per model, with MAC and emission dominating the AAOD errors over Amazon and Africa, respectively. In addition to primary emissions, our analysis suggests substantial formation of secondary organic aerosols over the Amazon but not over Africa. Furthermore, we find that differences in direct aerosol radiative effects between models decrease by threefold over the BB source and outflow regions after correcting the identified errors. This highlights the potential to greatly reduce the uncertainty in the most uncertain radiative forcing agent.

DOI： 10.1126/sciadv.adi3568

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41558-023-01883-2

Language：Others   Publishing type：Research paper (scientific journal)  

Anthropogenic emissions of aerosols and precursor compounds are known to significantly affect the energy balance of the Earth-Atmosphere system, alter the formation of clouds and precipitation, and have a substantial impact on human health and the environment. Global models are an essential tool for examining the impacts of these emissions. In this study, we examine the sensitivity of model results to the assumed height of SO2 injection, seasonality of SO2 and black carbon (BC) particulate emissions, and the assumed fraction of SO2 emissions that is injected into the atmosphere as particulate phase sulfate (SO4) in 11 climate and chemistry models, including both chemical transport models and the atmospheric component of Earth system models. We find large variation in atmospheric lifetime across models for SO2, SO4, and BC, with a particularly large relative variation for SO2, which indicates that fundamental aspects of atmospheric sulfur chemistry remain uncertain. Of the perturbations examined in this study, the assumed height of SO2 injection had the largest overall impacts, particularly on global mean net radiative flux (maximum difference of-0.35gWgm-2), SO2 lifetime over Northern Hemisphere land (maximum difference of 0.8gd), surface SO2 concentration (up to 59g% decrease), and surface sulfate concentration (up to 23g% increase). Emitting SO2 at height consistently increased SO2 and SO4 column burdens and shortwave cooling, with varying magnitudes, but had inconsistent effects across models on the sign of the change in implied cloud forcing. The assumed SO4 emission fraction also had a significant impact on net radiative flux and surface sulfate concentration. Because these properties are not standardized across models this is a source of inter-model diversity typically neglected in model intercomparisons. These results imply a need to ensure that anthropogenic emission injection height and SO4 emission fraction are accurately and consistently represented in global models.

DOI： 10.5194/acp-23-14779-2023

Language：English   Publishing type：Research paper (scientific journal)  

Abstract

Iron availability limits marine ecosystem activities in large areas of the ocean. However, the sources and seasonal supply of iron, critically important for controlling surface ocean biogeochemistry and carbon cycling, are poorly understood. The western subarctic Pacific is a high-nutrient and low-chlorophyll region, and despite high concentrations of macronutrients, iron limits phytoplankton production in summer. Here, we determine the seasonal deposition flux of Asian dust using scanning electron microscope–cathodoluminescence analysis of single quartz particles derived from the western subarctic Pacific during 2003–2022 to trace provenance. We found a high (up to 6.9 mg m⁻² day⁻¹) deposition flux of Asian dust in May, June, and early July, with an annual average of 1.0 ± 0.2 mg m⁻² day⁻¹. The supply of dissolved-iron flux calculated from Asian dust was 0.9 ± 0.3 µg m⁻² day⁻¹ during the high productivity season (April–July), which is approximately half that from the deeper part of the ocean, calculated from vertical profiles of dissolved iron. Our study provides a reliable approach for estimating iron supply from dust to the surface ocean that may be critical for sustaining biological productivity under future ocean stratification, which suppresses nutrient supply from the subsurface ocean.

DOI： 10.1038/s41598-023-41201-6

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. Changes in anthropogenic aerosol emissions have strongly contributed to global and regional trends in temperature, precipitation, and other climate characteristics and have been one of the dominant drivers of decadal trends in Asian and African precipitation. These and other influences on regional climate from changes in aerosol emissions are expected to continue and potentially strengthen in the coming decades. However, a combination of large uncertainties in emission pathways, radiative forcing, and the dynamical response to forcing makes anthropogenic aerosol a key factor in the spread of near-term climate projections, particularly on regional scales, and therefore an important one to constrain. For example, in terms of future emission pathways, the uncertainty in future global aerosol and precursor gas emissions by 2050 is as large as the total increase in emissions since 1850. In terms of aerosol effective radiative forcing, which remains the largest source of uncertainty in future climate change projections, CMIP6 models span a factor of 5, from −0.3 to −1.5 W m−2. Both of these sources of uncertainty are exacerbated on regional scales. The Regional Aerosol Model Intercomparison Project (RAMIP) will deliver experiments designed to quantify the role of regional aerosol emissions changes in near-term projections. This is unlike any prior MIP, where the focus has been on changes in global emissions and/or very idealised aerosol experiments. Perturbing regional emissions makes RAMIP novel from a scientific standpoint and links the intended analyses more directly to mitigation and adaptation policy issues. From a science perspective, there is limited information on how realistic regional aerosol emissions impact local as well as remote climate conditions. Here, RAMIP will enable an evaluation of the full range of potential influences of realistic and regionally varied aerosol emission changes on near-future climate. From the policy perspective, RAMIP addresses the burning question of how local and remote decisions affecting emissions of aerosols influence climate change in any given region. Here, RAMIP will provide the information needed to make direct links between regional climate policies and regional climate change. RAMIP experiments are designed to explore sensitivities to aerosol type and location and provide improved constraints on uncertainties driven by aerosol radiative forcing and the dynamical response to aerosol changes. The core experiments will assess the effects of differences in future global and regional (Africa and the Middle East, East Asia, North America and Europe, and South Asia) aerosol emission trajectories through 2051, while optional experiments will test the nonlinear effects of varying emission locations and aerosol types along this future trajectory. All experiments are based on the shared socioeconomic pathways and are intended to be performed with 6th Climate Model Intercomparison Project (CMIP6) generation models, initialised from the CMIP6 historical experiments, to facilitate comparisons with existing projections. Requested outputs will enable the analysis of the role of aerosol in near-future changes in, for example, temperature and precipitation means and extremes, storms, and air quality.

DOI： 10.5194/gmd-16-4451-2023

Language：English   Publishing type：Research paper (scientific journal)  

Abstract

The climate system responds to changes in the amount of atmospheric greenhouse gases or aerosols through rapid processes, triggered within hours and days, and through slower processes, where the full response may only be seen after centuries. In this paper, we aim to elucidate the mechanisms operating on time scales of hours to years to better understand the response of key climate quantities such as energy fluxes, temperature, and precipitation after a sudden increase in either carbon dioxide (CO₂), black carbon (BC), or sulfate (SO₄) aerosols. The results are based on idealized simulations from six global climate models. We find that the effect of changing ocean temperatures kicks in after a couple of months. Rapid precipitation reductions start occurring instantly and are established after just a few days. For BC, they constitute most of the equilibrium response. For CO₂ and SO₄, the magnitude of the precipitation response gradually increases as surface warming/cooling evolves, and for CO₂, the sign of the response changes from negative to positive after 2 years. Rapid cloud adjustments are typically established within the first 24 h, and while the magnitude of cloud feedbacks for CO₂ and SO₄ increases over time, the geographical pattern of the equilibrium cloud change is present already after the first year. While there are model differences, our work underscores the overall similarity of the major time-varying processes and responses simulated by current global models and hence the robustness of key features of simulated responses to historical and future anthropogenic forcing.

Significance Statement

How does the climate system respond to a change in the amount of atmospheric greenhouse gases or aerosols? Some processes are rapid, responding within hours and days. Others are slow, and the full response to a forcing of the climate may only be seen after centuries. In this paper, we use six global climate models to investigate the time scales of climate responses to carbon dioxide, black carbon, and sulfate, focusing on key climate quantities, such as temperature, precipitation, and clouds. While there are ample model differences, our work underscores the overall similarity of the major time-varying processes and responses simulated by current global models and hence the robustness of key features of simulated responses to historical and future anthropogenic forcing.

DOI： 10.1175/jcli-d-22-0513.1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2022jc019249

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3389/fmars.2023.1052286

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s43247-022-00660-x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41467-022-33680-4

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-22-11009-2022

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41597-022-01194-9

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. Aerosol-induced absorption of shortwave radiation can modify the climate through local atmospheric heating, which affects lapse rates,
precipitation, and cloud formation. Presently, the total amount of aerosol
absorption is poorly constrained, and the main absorbing aerosol species
(black carbon (BC), organic aerosols (OA), and mineral dust) are diversely
quantified in global climate models. As part of the third phase of the
Aerosol Comparisons between Observations and
Models (AeroCom) intercomparison initiative (AeroCom phase III), we here
document the distribution and magnitude of aerosol absorption in current
global aerosol models and quantify the sources of intermodel spread,
highlighting the difficulties of attributing absorption to different
species. In total, 15 models have provided total present-day absorption at 550 nm
(using year 2010 emissions), 11 of which have provided absorption per
absorbing species. The multi-model global annual mean total absorption
aerosol optical depth (AAOD) is 0.0054 (0.0020 to 0.0098; 550 nm), with the range given as the minimum and maximum model values. This is 28 &#37; higher compared to the 0.0042 (0.0021 to 0.0076) multi-model mean in AeroCom phase II (using year 2000 emissions), but the difference is within 1 standard
deviation, which, in this study, is 0.0023 (0.0019 in Phase II). Of the summed component AAOD, 60 &#37; (range 36 &#37;–84 &#37;) is estimated to be due to BC, 31 &#37; (12 &#37;–49 &#37;) is due to dust, and 11 &#37; (0 &#37;–24 &#37;) is due to OA; however, the components are not independent in terms of their absorbing efficiency. In models with internal mixtures of absorbing aerosols, a major
challenge is the lack of a common and simple method to attribute absorption
to the different absorbing species. Therefore, when possible, the models
with internally mixed aerosols in the present study have performed
simulations using the same method for estimating absorption due to BC, OA,
and dust, namely by removing it and comparing runs with and without the
absorbing species. We discuss the challenges of attributing absorption to
different species; we compare burden, refractive indices, and density; and
we contrast models with internal mixing to models with external mixing. The
model mean BC mass absorption coefficient (MAC) value is 10.1 (3.1 to 17.7) m2 g−1 (550 nm), and the model mean BC AAOD is 0.0030 (0.0007 to
0.0077). The difference in lifetime (and burden) in the models explains as
much of the BC AAOD spread as the difference in BC MAC values. The
difference in the spectral dependency between the models is striking. Several models have an absorption Ångstrøm exponent (AAE) close to 1, which likely is too low given current knowledge of spectral aerosol optical properties. Most models do not account for brown carbon and underestimate the spectral dependency for OA.

DOI： 10.5194/acp-21-15929-2021

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2021ms002584

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. For the radiative impact of individual climate forcings,
most previous studies focused on the global mean values at the top of the
atmosphere (TOA), and less attention has been paid to surface processes,
especially for black carbon (BC) aerosols. In this study, the surface radiative
responses to five different forcing agents were analyzed by using idealized
model simulations. Our analyses reveal that for greenhouse gases, solar
irradiance, and scattering aerosols, the surface temperature changes are
mainly dictated by the changes of surface radiative heating, but for BC,
surface energy redistribution between different components plays a more
crucial role. Globally, when a unit BC forcing is imposed at TOA, the net
shortwave radiation at the surface decreases by -5.87±0.67 W m−2 (W m−2)−1 (averaged over global land without Antarctica), which is
partially offset by increased downward longwave radiation (2.32±0.38 W m−2 (W m−2)−1 from the warmer atmosphere, causing a net
decrease in the incoming downward surface radiation of -3.56±0.60 W m−2 (W m−2)−1. Despite a reduction in the downward radiation
energy, the surface air temperature still increases by 0.25±0.08 K
because of less efficient energy dissipation, manifested by reduced surface
sensible (-2.88±0.43 W m−2 (W m−2)−1) and latent heat flux
(-1.54±0.27 W m−2 (W m−2)−1), as well as a decrease in
Bowen ratio (-0.20±0.07 (W m−2)−1). Such reductions of turbulent
fluxes can be largely explained by enhanced air stability (0.07±0.02 K (W m−2)−1), measured as the difference of the potential temperature
between 925 hPa and surface, and reduced surface wind speed (-0.05±0.01 m s−1 (W m−2)−1). The enhanced stability is due to the faster
atmospheric warming relative to the surface, whereas the reduced wind speed
can be partially explained by enhanced stability and reduced Equator-to-pole
atmospheric temperature gradient. These rapid adjustments under BC forcing
occur in the lower atmosphere and propagate downward to influence the
surface energy redistribution and thus surface temperature response, which
is not observed under greenhouse gases or scattering aerosols. Our study
provides new insights into the impact of absorbing aerosols on surface
energy balance and surface temperature response.

DOI： 10.5194/acp-21-13797-2021

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. Within the framework of the AeroCom (Aerosol Comparisons between Observations and Models) initiative, the state-of-the-art modelling of aerosol optical properties is assessed from 14 global models participating in the phase III control experiment (AP3). The models are similar to CMIP6/AerChemMIP Earth System Models (ESMs) and provide a robust multi-model ensemble. Inter-model spread of aerosol species lifetimes and emissions appears to be similar to that of mass extinction coefficients (MECs), suggesting that aerosol optical depth (AOD) uncertainties are associated with a broad spectrum of parameterised aerosol processes. Total AOD is approximately the same as in AeroCom phase I (AP1) simulations. However, we find a 50 &#37; decrease in the optical depth (OD) of black carbon (BC), attributable to a combination of decreased emissions and lifetimes. Relative contributions from sea salt (SS) and dust (DU) have shifted from being approximately equal in AP1 to SS contributing about 2∕3 of the natural AOD in AP3. This shift is linked with a decrease in DU mass burden, a lower DU MEC, and a slight decrease in DU lifetime, suggesting coarser DU particle sizes in AP3 compared to AP1. Relative to observations, the AP3 ensemble median and most of the participating models underestimate all aerosol optical properties investigated, that is, total AOD as well as fine and coarse AOD (AODf, AODc), Ångström exponent (AE), dry surface scattering (SCdry), and absorption (ACdry) coefficients. Compared to AERONET, the models underestimate total AOD by ca. 21 &#37; ± 20 &#37; (as inferred from the ensemble median and interquartile range). Against satellite data, the ensemble AOD biases range from −37 &#37; (MODIS-Terra) to −16 &#37; (MERGED-FMI, a multi-satellite AOD product), which we explain by differences between individual satellites and AERONET measurements themselves. Correlation coefficients (R) between model and observation AOD records are generally high (R>0.75), suggesting that the models are capable of capturing spatio-temporal variations in AOD. We find a much larger underestimate in coarse AODc (∼ −45 &#37; ± 25 &#37;) than in fine AODf (∼ −15 &#37; ± 25 &#37;) with slightly increased inter-model spread compared to total AOD. These results indicate problems in the modelling of DU and SS. The AODc bias is likely due to missing DU over continental land masses (particularly over the United States, SE Asia, and S. America), while marine AERONET sites and the AATSR SU satellite data suggest more moderate oceanic biases in AODc. Column AEs are underestimated by about 10 &#37; ± 16 &#37;. For situations in which measurements show AE > 2, models underestimate AERONET AE by ca. 35 &#37;. In contrast, all models (but one) exhibit large overestimates in AE when coarse aerosol dominates (bias ca. +140 &#37; if observed AE < 0.5). Simulated AE does not span the observed AE variability. These results indicate that models overestimate particle size (or underestimate the fine-mode fraction) for fine-dominated aerosol and underestimate size (or overestimate the fine-mode fraction) for coarse-dominated aerosol. This must have implications for lifetime, water uptake, scattering enhancement, and the aerosol radiative effect, which we can not quantify at this moment. Comparison against Global Atmosphere Watch (GAW) in situ data results in mean bias and inter-model variations of −35 &#37; ± 25 &#37; and −20 &#37; ± 18 &#37; for SCdry and ACdry, respectively. The larger underestimate of SCdry than ACdry suggests the models will simulate an aerosol single scattering albedo that is too low. The larger underestimate of SCdry than ambient air AOD is consistent with recent findings that models overestimate scattering enhancement due to hygroscopic growth. The broadly consistent negative bias in AOD and surface scattering suggests an underestimate of aerosol radiative effects in current global aerosol models. Considerable inter-model diversity in the simulated optical properties is often found in regions that are, unfortunately, not or only sparsely covered by ground-based observations. This includes, for instance, the Sahara, Amazonia, central Australia, and the South Pacific. This highlights the need for a better site coverage in the observations, which would enable us to better assess the models, but also the performance of satellite products in these regions. Using fine-mode AOD as a proxy for present-day aerosol forcing estimates, our results suggest that models underestimate aerosol forcing by ca. −15 &#37;, however, with a considerably large interquartile range, suggesting a spread between −35 &#37; and +10 &#37;.

DOI： 10.5194/acp-21-87-2021

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. Feedbacks play a fundamental role in determining the magnitude of the
response of the climate system to external forcing, such as from
anthropogenic emissions. The latest generation of Earth system models
includes aerosol and chemistry components that interact with each other and
with the biosphere. These interactions introduce a complex web of feedbacks
that is important to understand and quantify. This paper addresses multiple pathways for aerosol and chemical feedbacks in
Earth system models. These focus on changes in natural emissions (dust, sea
salt, dimethyl sulfide, biogenic volatile organic compounds (BVOCs) and
lightning) and changes in reaction rates for methane and ozone chemistry.
The feedback terms are then given by the sensitivity of a pathway to climate
change multiplied by the radiative effect of the change. We find that the overall climate feedback through chemistry and aerosols is
negative in the sixth Coupled Model Intercomparison Project (CMIP6) Earth
system models due to increased negative forcing from aerosols in a climate
with warmer surface temperatures following a quadrupling of CO2
concentrations. This is principally due to increased emissions of sea salt
and BVOCs which are sensitive to climate change and cause strong
negative radiative forcings. Increased chemical loss of ozone and methane
also contributes to a negative feedback. However, overall methane lifetime is
expected to increase in a warmer climate due to increased BVOCs. Increased
emissions of methane from wetlands would also offset some of the negative
feedbacks. The CMIP6 experimental design did not allow the methane lifetime
or methane emission changes to affect climate, so we found a robust negative
contribution from interactive aerosols and chemistry to climate sensitivity
in CMIP6 Earth system models.

DOI： 10.5194/acp-21-1105-2021

Language：English   Publishing type：Research paper (scientific journal)  

This paper quantifies the pre-industrial (1850) to present-day (2014) effective radiative forcing (ERF) of anthropogenic emissions of NOX, volatile organic compounds (VOCs; including CO), SO2, NH3, black carbon, organic carbon, and concentrations of methane, N2O and ozone-depleting halocarbons, using CMIP6 models. Concentration and emission changes of reactive species can cause multiple changes in the composition of radiatively active species: tropospheric ozone, stratospheric ozone, stratospheric water vapour, secondary inorganic and organic aerosol, and methane. Where possible we break down the ERFs from each emitted species into the contributions from the composition changes. The ERFs are calculated for each of the models that participated in the AerChemMIP experiments as part of the CMIP6 project, where the relevant model output was available.The 1850 to 2014 multi-model mean ERFs (+/- standard deviations) are -1.03 +/- 0.37 W m(-2) for SO2 emissions, -0.25 +/- 0.09 W m(-2) for organic carbon (OC), 0.15 +/- 0.17 W m(-2) for black carbon (BC) and -0.07 +/- 0.01 W m(-2) for NH3. For the combined aerosols (in the piClim-aer experiment) it is -1.01 +/- 0.25 W m(-2). The multi-model means for the reactive well-mixed greenhouse gases (including any effects on ozone and aerosol chemistry) are 0.67 +/- 0.17 W m(-2) for methane (CH4), 0.26 +/- 0.07 W m(-2) for nitrous oxide (N2O) and 0.12 +/- 0.2 W m(-2) for ozone-depleting halocarbons (HC). Emissions of the ozone precursors nitrogen oxides (NOx) volatile organic compounds and both together (O-3) lead to ERFs of 0.14 +/- 0.13, 0.09 +/- 0.14 and 0.20 +/- 0.07 W m(-2) respectively. The differences in ERFs calculated for the different models reflect differences in the complexity of their aerosol and chemistry schemes, especially in the case of methane where tropospheric chemistry captures increased forcing from ozone production.

DOI： 10.5194/acp-21-853-2021

Language：English   Publishing type：Research paper (scientific journal)  

© 2020, The Author(s). Radiative forcing (RF) time series for total ozone from 1850 up to the present day are calculated based on historical simulations of ozone from 10 climate models contributing to the Coupled Model Intercomparison Project Phase 6 (CMIP6). In addition, RF is calculated for ozone fields prepared as an input for CMIP6 models without chemistry schemes and from a chemical transport model simulation. A radiative kernel for ozone is constructed and used to derive the RF. The ozone RF in 2010 (2005–2014) relative to 1850 is 0.35 W m−2 [0.08–0.61] (5–95&#37; uncertainty range) based on models with both tropospheric and stratospheric chemistry. One of these models has a negative present-day total ozone RF. Excluding this model, the present-day ozone RF increases to 0.39 W m−2 [0.27–0.51] (5–95&#37; uncertainty range). The rest of the models have RF close to or stronger than the RF time series assessed by the Intergovernmental Panel on Climate Change in the fifth assessment report with the primary driver likely being the new precursor emissions used in CMIP6. The rapid adjustments beyond stratospheric temperature are estimated to be weak and thus the RF is a good measure of effective radiative forcing.

DOI： 10.1038/s41612-020-00131-0

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2019jd032097

Language：English   Publishing type：Research paper (scientific journal)  

Anthropogenic aerosol emissions have increased considerably over the last century, but climate effects and quantification of the emissions are highly uncertain as one goes back in time. This uncertainty is partly due to a lack of observations in the pre-satellite era, making the observations we do have before 1990 additionally valuable. Aerosols suspended in the atmosphere scatter and absorb incoming solar radiation and thereby alter the Earth's surface energy balance. Previous studies show that Earth system models (ESMs) do not adequately represent surface energy fluxes over the historical era. We investigated global and regional aerosol effects over the time period 1961-2014 by looking at surface downwelling shortwave radiation (SDSR). We used observations from ground stations as well as multiple experiments from eight ESMs participating in the Coupled Model Intercomparison Project Version 6 (CMIP6). Our results show that this subset of models reproduces the observed transient SDSR well in Europe but poorly in China. We suggest that this may be attributed to missing emissions of sulfur dioxide in China, sulfur dioxide being a precursor to sulfate, which is a highly reflective aerosol and responsible for more reflective clouds. The emissions of sulfur dioxide used in the models do not show a temporal pattern that could explain observed SDSR evolution over China. The results from various aerosol emission perturbation experiments from DAMIP, RFMIP and AerChemMIP show that only simulations containing anthropogenic aerosol emissions show dimming, even if the dimming is underestimated. Simulated clear-sky and all-sky SDSR do not differ greatly, suggesting that cloud cover changes are not a dominant cause of the biased SDSR evolution in the simulations. Therefore we suggest that the discrepancy between modeled and observed SDSR evolution is partly caused by erroneous aerosol and aerosol precursor emission inventories. This is an important finding as it may help interpret whether ESMs reproduce the historical climate evolution for the right or wrong reason.

DOI： 10.5194/acp-20-16023-2020

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2151/sola.2020-040

Language：English   Publishing type：Research paper (scientific journal)  

<title>Abstract</title>Rapid adjustments occur after initial perturbation of an external climate driver (e.g., CO₂) and involve changes in, e.g. atmospheric temperature, water vapour and clouds, independent of sea surface temperature changes. Knowledge of such adjustments is necessary to estimate effective radiative forcing (ERF), a useful indicator of surface temperature change, and to understand global precipitation changes due to different drivers. Yet, rapid adjustments have not previously been analysed in any detail for certain compounds, including halocarbons and N₂O. Here we use several global climate models combined with radiative kernel calculations to show that individual rapid adjustment terms due to CFC-11, CFC-12 and N₂O are substantial, but that the resulting flux changes approximately cancel at the top-of-atmosphere due to compensating effects. Our results further indicate that radiative forcing (which includes stratospheric temperature adjustment) is a reasonable approximation for ERF. These CFCs lead to a larger increase in precipitation per kelvin surface temperature change (2.2 ± 0.3&#37; K⁻¹) compared to other well-mixed greenhouse gases (1.4 ± 0.3&#37; K⁻¹ for CO₂). This is largely due to rapid upper tropospheric warming and cloud adjustments, which lead to enhanced atmospheric radiative cooling (and hence a precipitation increase) and partly compensate increased atmospheric radiative heating (i.e. which is associated with a precipitation decrease) from the instantaneous perturbation.

DOI： 10.1038/s41612-020-00150-x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1186/s40645-020-00351-1

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. This study presents a multiparameter analysis of aerosol trends over the last 2 decades at regional and global scales. Regional time series have been computed for a set of nine optical, chemical-composition and mass aerosol properties by using the observations from several ground-based networks. From these regional time series the aerosol trends have been derived for the different regions of the world. Most of the properties related to aerosol loading exhibit negative trends, both at the surface and in the total atmospheric column. Significant decreases in aerosol optical depth (AOD) are found in Europe, North America, South America, North Africa and Asia, ranging from −1.2 &#37; yr−1 to −3.1 &#37; yr−1. An error and representativity analysis of the spatially and temporally limited observational data has been performed using model data subsets in order to investigate how much the observed trends represent the actual trends happening in the regions over the full study period from 2000 to 2014. This analysis reveals that significant uncertainty is associated with some of the regional trends due to time and space sampling deficiencies. The set of observed regional trends has then been used for the evaluation of 10 models (6 AeroCom phase III models and 4 CMIP6 models) and the CAMS reanalysis dataset and of their skills in reproducing the aerosol trends. Model performance is found to vary depending on the parameters and the regions of the world. The models tend to capture trends in AOD, the column Ångström exponent, sulfate and particulate matter well (except in North Africa), but they show larger discrepancies for coarse-mode AOD. The rather good agreement of the trends, across different aerosol parameters between models and observations, when co-locating them in time and space, implies that global model trends, including those in poorly monitored regions, are likely correct. The models can help to provide a global picture of the aerosol trends by filling the gaps in regions not covered by observations. The calculation of aerosol trends at a global scale reveals a different picture from that depicted by solely relying on ground-based observations. Using a model with complete diagnostics (NorESM2), we find a global increase in AOD of about 0.2 &#37; yr−1 between 2000 and 2014, primarily caused by an increase in the loads of organic aerosols, sulfate and black carbon.

DOI： 10.5194/acp-20-13355-2020

Language：English   Publishing type：Research paper (scientific journal)  

Poor air quality is currently responsible for large impacts on human health across the world. In addition, the air pollutants ozone (O-3) and particulate matter less than 2.5 mu m in diameter (PM2.5) are also radiatively active in the atmosphere and can influence Earth's climate. It is important to understand the effect of air quality and climate mitigation measures over the historical period and in different future scenarios to ascertain any impacts from air pollutants on both climate and human health. The Coupled Model Intercomparison Project Phase 6 (CMIP6) presents an opportunity to analyse the change in air pollutants simulated by the current generation of climate and Earth system models that include a representation of chemistry and aerosols (particulate matter). The shared socio-economic pathways (SSPs) used within CMIP6 encompass a wide range of trajectories in precursor emissions and climate change, allowing for an improved analysis of future changes to air pollutants. Firstly, we conduct an evaluation of the available CMIP6 models against surface observations of O-3 and PM2.5. CMIP6 models consistently overestimate observed surface O-3 concentrations across most regions and in most seasons by up to 16 ppb, with a large diversity in simulated values over Northern Hemisphere continental regions. Conversely, observed surface PM(2.5 )concentrations are consistently underestimated in CMIP6 models by up to 10 mu gm(-3), particularly for the Northern Hemisphere winter months, with the largest model diversity near natural emission source regions. The biases in CMIP6 models when compared to observations of O-3 and PM2.5 are similar to those found in previous studies. Over the historical period (1850-2014) large increases in both surface O-3 and PM2.5 are simulated by the CMIP6 models across all regions, particularly over the mid to late 20th century, when anthropogenic emissions increase markedly. Large regional historical changes are simulated for both pollutants across East and South Asia with an annual mean increase of up to 40 ppb for O-3 and 12 mu g m(-3) for PM2.5. In future scenarios containing strong air quality and climate mitigation measures (ssp126), annual mean concentrations of air pollutants are substantially reduced across all regions by up to 15 ppb for O-3 and 12 mu g m(-3) for PM2.5. However, for scenarios that encompass weak action on mitigating climate and reducing air pollutant emissions (ssp370), annual mean increases in both surface O-3 (up 10 ppb) and PM2.5 (up to 8 mu g m(-3)) are simulated across most regions, although, for regions like North America and Europe small reductions in PM2.5 are simulated due to the regional reduction in precursor emissions in this scenario. A comparison of simulated regional changes in both surface O-3 and PM2.5 from individual CMIP6 models highlights important regional differences due to the simulated interaction of aerosols, chemistry, climate and natural emission sources within models. The projection of regional air pollutant concentrations from the latest climate and Earth system models used within CMIP6 shows that the particular future trajectory of climate and air quality mitigation measures could have important consequences for regional air quality, human health and near-term climate.Differences between individual models emphasise the importance of understanding how future Earth system feedbacks influence natural emission sources, e.g. response of biogenic emissions under climate change.

DOI： 10.5194/acp-20-14547-2020

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. The diurnal temperature range (DTR) (or difference
between the maximum and minimum temperature within a day) is one of many
climate parameters that affects health, agriculture and society.
Understanding how DTR evolves under global warming is therefore crucial.
Physically different drivers of climate change, such as greenhouse gases and
aerosols, have distinct influences on global and regional climate.
Therefore, predicting the future evolution of DTR requires knowledge of the
effects of individual climate forcers, as well as of the future emissions
mix, in particular in high-emission regions. Using global climate model
simulations from the Precipitation Driver and Response Model Intercomparison
Project (PDRMIP), we investigate how idealized changes in the atmospheric
levels of a greenhouse gas (CO2) and aerosols (black carbon and
sulfate) influence DTR (globally and in selected regions). We find broad
geographical patterns of annual mean change that are similar between climate
drivers, pointing to a generalized response to global warming which is not
defined by the individual forcing agents. Seasonal and regional differences,
however, are substantial, which highlights the potential importance of local
background conditions and feedbacks. While differences in DTR responses
among drivers are minor in Europe and North America, there are distinctly
different DTR responses to aerosols and greenhouse gas perturbations over
India and China, where present aerosol emissions are particularly high. BC
induces substantial reductions in DTR, which we attribute to strong modeled
BC-induced cloud responses in these regions.

DOI： 10.5194/acp-20-13467-2020

Language：English   Publishing type：Research paper (scientific journal)  

<title>Abstract</title>Rapid adjustments—the response of meteorology to external forcing while sea surface temperatures (SST) and sea ice are held fixed—can affect the midlatitude circulation and contribute to long-term forced circulation responses in climate simulations. This study examines rapid adjustments in the Southern Hemisphere (SH) circulation using nine models from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), which perform fixed SST and coupled ocean experiments for five perturbations: a doubling of carbon dioxide (2xCO2), a tripling of methane (3xCH4), a fivefold increase in sulfate aerosol (5xSO4), a tenfold increase in black carbon aerosol (10xBC), and a 2&#37; increase in solar constant (2&#37;Sol). In the coupled experiments, the SH eddy-driven jet shifts poleward and strengthens for forcings that produce global warming (and vice versa for 5xSO4), with the strongest response found in austral summer. In austral winter, the responses project more strongly onto a change in jet strength. For 10xBC, which induces strong shortwave absorption, the multimodel mean (MMM) rapid adjustment in DJF jet latitude is ~75&#37; of the change in the coupled simulations. For the other forcings, which induce larger SST changes, the effect of SST-mediated feedbacks on the SH circulation is larger than the rapid adjustment. Nevertheless, for these perturbations the magnitude of the MMM jet shift due to the rapid adjustment is still around 20&#37;–30&#37; of that in the coupled experiments. The results demonstrate the need to understand the mechanisms for rapid adjustments in the midlatitude circulation, in addition to the effect of changing SSTs.

DOI： 10.1175/jcli-d-19-1015.1

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. Complex aerosol–cloud–precipitation interactions lead to large differences in estimates of aerosol impacts on climate among general circulation models (GCMs) and satellite retrievals. Typically, precipitating hydrometeors are treated diagnostically in most GCMs, and their radiative effects are ignored. Here, we quantify how the treatment of precipitation influences the simulated effective radiative forcing due to aerosol–cloud interactions (ERFaci) using a state-of-the-art GCM with a two-moment prognostic precipitation scheme that incorporates the radiative effect of precipitating particles, and we investigate how microphysical process representations are related to macroscopic climate effects. Prognostic precipitation substantially weakens the magnitude of ERFaci (by approximately 54 &#37;) compared with the traditional diagnostic scheme, and this is the result of the increased longwave (warming) and weakened shortwave (cooling) components of ERFaci. The former is attributed to additional adjustment processes induced by falling snow, and the latter stems largely from riming of snow by collection of cloud droplets. The significant reduction in ERFaci does not occur without prognostic snow, which contributes mainly by buffering the cloud response to aerosol perturbations through depleting cloud water via collection. Prognostic precipitation also alters the regional pattern of ERFaci, particularly over northern midlatitudes where snow is abundant. The treatment of precipitation is thus a highly influential controlling factor of ERFaci, contributing more than other uncertain “tunable” processes related to aerosol–cloud–precipitation interactions. This change in ERFaci caused by the treatment of precipitation is large enough to explain the existing difference in ERFaci between GCMs and observations.

DOI： 10.5194/acp-20-13771-2020

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. Black carbon (BC) aerosols emitted from natural and anthropogenic sources
induce positive radiative forcing and global warming,
which in turn significantly affect the Asian summer monsoon (ASM).
However, many aspects of the BC effect on the ASM remain elusive
and largely inconsistent among previous studies, which is strongly dependent on
different low-level thermal feedbacks over the Asian continent and the surrounding ocean.
This study examines the response of the ASM to BC forcing in comparison with
the effect of doubled greenhouse gases (GHGs) by analyzing the Precipitation Driver
Response Model Intercomparison Project (PDRMIP) simulations
under an extremely high BC level (10 times modern global BC emissions or concentrations,
labeled BC×10) from nine global climate models (GCMs).
The results show that although BC and GHGs both enhance the ASM precipitation minus evaporation (P−E; a 13.6 &#37; increase for BC forcing and 12.1 &#37; for GHGs from the nine-model ensemble, respectively),
there exists a much larger uncertainty in changes in ASM P−E induced by BC than by GHGs.
The summer P−E is increased by 7.7 &#37; to 15.3 &#37; due to these two forcings
over three subregions, including East Asian, South Asian and western North Pacific monsoon regions.
Further analysis of moisture budget reveals distinct mechanisms controlling the increases in ASM P−E induced by BC and GHGs.
The change in ASM P−E by BC is dominated by the dynamic effect due to the enhanced large-scale monsoon circulation,
whereas the GHG-induced change is dominated by the thermodynamic effect through increasing atmospheric water vapor.
Radiative forcing of BC significantly increases the upper-level atmospheric temperature
over the Asian region to enhance the upper-level meridional land–sea thermal gradient (MLOTG),
resulting in a northward shift of the upper-level subtropical westerly jet
and an enhancement of the low-level monsoon circulation,
whereas radiative forcing of GHGs significantly increases the tropical upper-level temperature,
which reduces the upper-level MLOTG and suppresses the low-level monsoonal circulation.
Hence, our results indicate a different mechanism of BC climate effects
under the extremely high BC level: that BC forcing significantly
enhances the upper-level atmospheric temperature over the Asian region,
determining ASM changes, instead of low-level thermal feedbacks as indicated by previous studies.

DOI： 10.5194/acp-20-11823-2020

Language：English   Publishing type：Research paper (scientific journal)  

The effective radiative forcing (ERF) of anthropogenic aerosol can be more representative of the eventual climate response than other radiative forcing. We incorporate aerosol–cloud interaction into the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System (CAS-FGOALS-f3-L) by coupling an existing aerosol module named the Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) and quantified the ERF and its primary components (i.e., effective radiative forcing of aerosol-radiation interactions (ERFari) and aerosol-cloud interactions (ERFaci)) based on the protocol of current Coupled Model Intercomparison Project phase 6 (CMIP6). The spatial distribution of the shortwave ERFari and ERFaci in CAS-FGOALS-f3-L are comparable with that of most available CMIP6 models. The global mean 2014–1850 shortwave ERFari in CAS-FGOALS-f3-L (−0.27 W m−2) is close to the multi-model means in 4 available models (−0.29 W m−2), whereas the assessing shortwave ERFaci (−1.04 W m−2) and shortwave ERF (−1.36 W m−2) are slightly stronger than the multi-model means, illustrating that the CAS-FGOALS-f3-L can reproduce the aerosol radiation effect reasonably well. However, significant diversity exists in the ERF, especially in the dominated component ERFaci, implying that the uncertainty is still large.

DOI： 10.3390/atmos11101115

Language：English   Publishing type：Research paper (scientific journal)  

Abstract. It is important to understand how future environmental policies will impact both climate change and air pollution. Although targeting near-term climate forcers (NTCFs), defined here as aerosols, tropospheric ozone, and precursor gases, should improve air quality, NTCF reductions will also impact climate. Prior assessments of the impact of NTCF mitigation on air quality and climate have been limited. This is related to the idealized nature of some prior studies, simplified treatment of aerosols and chemically reactive gases, as well as a lack of a sufficiently large number of models to quantify model diversity and robust responses. Here, we quantify the 2015–2055 climate and air quality effects of non-methane NTCFs using nine state-of-the-art chemistry–climate model simulations conducted for the Aerosol and Chemistry Model Intercomparison Project (AerChemMIP). Simulations are driven by two future scenarios featuring similar increases in greenhouse gases (GHGs) but with “weak” (SSP3-7.0) versus “strong” (SSP3-7.0-lowNTCF) levels of air quality control measures. As SSP3-7.0 lacks climate policy and has the highest levels of NTCFs, our results (e.g., surface warming) represent an upper bound. Unsurprisingly, we find significant improvements in air quality under NTCF mitigation (strong versus weak air quality controls). Surface fine particulate matter (PM2.5) and ozone (O3) decrease by -2.2±0.32 µg m−3 and -4.6±0.88 ppb, respectively (changes quoted here are for the entire 2015–2055 time period; uncertainty represents the 95 &#37; confidence interval), over global land surfaces, with larger reductions in some regions including south and southeast Asia. Non-methane NTCF mitigation, however, leads to additional climate change due to the removal of aerosol which causes a net warming effect, including global mean surface temperature and precipitation increases of 0.25±0.12 K and 0.03±0.012 mm d−1, respectively. Similarly, increases in extreme weather indices, including the hottest and wettest days, also occur. Regionally, the largest warming and wetting occurs over Asia, including central and north Asia (0.66±0.20 K and 0.03±0.02 mm d−1), south Asia (0.47±0.16 K and 0.17±0.09 mm d−1), and east Asia (0.46±0.20 K and 0.15±0.06 mm d−1). Relatively large warming and wetting of the Arctic also occur at 0.59±0.36 K and 0.04±0.02 mm d−1, respectively. Similar surface warming occurs in model simulations with aerosol-only mitigation, implying weak cooling due to ozone reductions. Our findings suggest that future policies that aggressively target non-methane NTCF reductions will improve air quality but will lead to additional surface warming, particularly in Asia and the Arctic. Policies that address other NTCFs including methane, as well as carbon dioxide emissions, must also be adopted to meet climate mitigation goals.

DOI： 10.5194/acp-20-9641-2020

Language：English   Publishing type：Research paper (scientific journal)  

In this work, we use Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations from 10 Earth system models (ESMs) and general circulation models (GCMs) to study the fast climate responses on pre-industrial climate, due to present-day aerosols. All models carried out two sets of simulations: a control experiment with all forcings set to the year 1850 and a perturbation experiment with all forcings identical to the control, except for aerosols with precursor emissions set to the year 2014. In response to the pattern of all aerosols effective radiative forcing (ERF), the fast temperature responses are characterized by cooling over the continental areas, especially in the Northern Hemisphere, with the largest cooling over East Asia and India, sulfate being the dominant aerosol surface temperature driver for present-day emissions. In the Arctic there is a warming signal for winter in the ensemble mean of fast temperature responses, but the model-to-model variability is large, and it is presumably linked to aerosol-induced circulation changes. The largest fast precipitation responses are seen in the tropical belt regions, generally characterized by a reduction over continental regions and presumably a southward shift of the tropical rain belt. This is a characteristic and robust feature among most models in this study, associated with weakening of the monsoon systems around the globe (Asia, Africa and America) in response to hemispherically asymmetric cooling from a Northern Hemisphere aerosol perturbation, forcing possibly the Intertropical Convergence Zone (ITCZ) and tropical precipitation to shift away from the cooled hemisphere despite that aerosols' effects on temperature and precipitation are only partly realized in these simulations as the sea surface temperatures are kept fixed. An interesting feature in aerosol-induced circulation changes is a characteristic dipole pattern with intensification of the Icelandic Low and an anti- cyclonic anomaly over southeastern Europe, inducing warm air advection towards the northern polar latitudes in winter.

DOI： 10.5194/acp-20-8381-2020

Language：English   Publishing type：Research paper (scientific journal)  

© 2020 Royal Society of Chemistry. All rights reserved. The radiative forcing of the aerosol-radiation interaction can be decomposed into clear-sky and cloudy-sky portions. Two sets of multi-model simulations within Aerosol Comparisons between Observations and Models (AeroCom), combined with observational methods, and the time evolution of aerosol emissions over the industrial era show that the contribution from cloudy-sky regions is likely weak. A mean of the simulations considered is span classCombining double low lineinline-formula0.01±0.1/span&thinsp;W&thinsp;mspan classCombining double low lineinline-formula-2span. Multivariate data analysis of results from AeroCom Phase II shows that many factors influence the strength of the cloudy-sky contribution to the forcing of the aerosol-radiation interaction. Overall, single-scattering albedo of anthropogenic aerosols and the interaction of aerosols with the short-wave cloud radiative effects are found to be important factors. A more dedicated focus on the contribution from the cloud-free and cloud-covered sky fraction, respectively, to the aerosol-radiation interaction will benefit the quantification of the radiative forcing and its uncertainty range.

DOI： 10.5194/acp-20-8855-2020

Language：English   Publishing type：Research paper (scientific journal)  

© Author(s) 2020. The radiative forcing from aerosols (particularly through their interaction with clouds) remains one of the most uncertain components of the human forcing of the climate. Observation-based studies have typically found a smaller aerosol effective radiative forcing than in model simulations and were given preferential weighting in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). With their own sources of uncertainty, it is not clear that observation-based estimates are more reliable. Understanding the source of the model and observational differences is thus vital to reduce uncertainty in the impact of aerosols on the climate. These reported discrepancies arise from the different methods of separating the components of aerosol forcing used in model and observational studies. Applying the observational decomposition to global climate model (GCM) output, the two different lines of evidence are surprisingly similar, with a much better agreement on the magnitude of aerosol impacts on cloud properties. Cloud adjustments remain a significant source of uncertainty, particularly for ice clouds. However, they are consistent with the uncertainty from observation-based methods, with the liquid water path adjustment usually enhancing the Twomey effect by less than 50&#37;. Depending on different sets of assumptions, this work suggests that model and observation-based estimates could be more equally weighted in future synthesis studies.

DOI： 10.5194/acp-20-613-2020

Language：English   Publishing type：Research paper (scientific journal)  

©2019. American Geophysical Union. All Rights Reserved. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Dust is one of the dominant aerosol types over Asia and the North Pacific Ocean, but quantitative estimation of dust distribution and its contribution to the total regional aerosol load from observations is challenging due to the presence of significant anthropogenic and natural aerosols and the frequent influence of clouds over the region. This study presents the dust aerosol distributions over Asia and the North Pacific using simulations from five global models that participated in the AeroCom phase II model experiments, and from multiple satellite remote sensing and ground-based measurements of total aerosol optical depth and dust optical depth. We examine various aspects of aerosol and dust presence in our study domain: (1) the horizontal distribution, (2) the longitudinal gradient during trans-Pacific transport, (3) seasonal variations, (4) vertical profiles, and (5) model-simulated dust life cycles. This study reveals that dust optical depth model diversity is driven mostly by diversity in the dust source strength, followed by residence time and mass extinction efficiency.

DOI： 10.1029/2019JD030822

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2019JD030581

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-19-12887-2019

Language：English   Publishing type：Research paper (scientific journal)  

Background: Previous research has highlighted the importance of major atmospheric aerosols such as sulfate, through its precursor sulfur dioxide (SO2), black carbon (BC), and organic carbon (OC), and their effect on global climate regimes, specifically on their impact on particulate matter measuring ≤ 2.5 μm (PM2.5). Policy regulations have attempted to address the change in these major active aerosols and their impact on PM2.5, which would presumably have a cascading effect toward the change of health risks. Objective: This study aimed to determine how the change in the global emissions of anthropogenic aerosols affects health, particularly through the change in attributable mortality (AN) and years of life lost (YLL). This study also aimed to explore the importance of using AM/YLL in conveying air pollution health impact message. Methods: The Model for Interdisciplinary Research on Climate was used to estimate the gridded atmospheric PM2.5 by changing the emission of SO2, BC, and OC. Next, the emissions were utilized to estimate the associated cause-specific risks via an integrated exposure-response function, and its consequent health indicators, AM and YLL, per country. Results: OC change yielded the greatest benefit for all country income groups, particularly among low-middle-income countries. Utilizing either AM or YLL did not alter the order of benefits among upper-middle and high-income countries (UMIC/HIC); however, using either health indicator to express the order of benefit varied among low- and low-middle-income countries (LIC/LMIC). Conclusions: Global and country-specific mitigation efforts focusing on OC-related activities would yield substantial health benefits. Substantial aerosol emission reduction would greatly benefit high-emitting countries (i.e. China and India). Although no difference is found in the order of health outcome benefits in UMIC/HIC, caution is warranted in using either AM or YLL for health impact assessment in LIC/LMIC.

DOI： 10.1080/16549716.2019.1664130

Language：English   Publishing type：Research paper (scientific journal)  

© 2019 Copernicus GmbH. All rights reserved. The sixth version of the Model for Interdisciplinary Research on Climate (MIROC), called MIROC6, was cooperatively developed by a Japanese modeling community. In the present paper, simulated mean climate, internal climate variability, and climate sensitivity in MIROC6 are evaluated and briefly summarized in comparison with the previous version of our climate model (MIROC5) and observations. The results show that the overall reproducibility of mean climate and internal climate variability in MIROC6 is better than that in MIROC5. The tropical climate systems (e.g., summertime precipitation in the western Pacific and the eastward-propagating Madden-Julian oscillation) and the midlatitude atmospheric circulation (e.g., the westerlies, the polar night jet, and troposphere-stratosphere interactions) are significantly improved in MIROC6. These improvements can be attributed to the newly implemented parameterization for shallow convective processes and to the inclusion of the stratosphere. While there are significant differences in climates and variabilities between the two models, the effective climate sensitivity of 2.6K remains the same because the differences in radiative forcing and climate feedback tend to offset each other. With an aim towards contributing to the sixth phase of the Coupled Model Intercomparison Project, designated simulations tackling a wide range of climate science issues, as well as seasonal to decadal climate predictions and future climate projections, are currently ongoing using MIROC6.

DOI： 10.5194/gmd-12-2727-2019

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41612-019-0079-3

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2018JD029726

Language：English   Publishing type：Research paper (scientific journal)  

©2019. American Geophysical Union. All Rights Reserved. We compare six methods of estimating effective radiative forcing (ERF) using a set of atmosphere-ocean general circulation models. This is the first multiforcing agent, multimodel evaluation of ERF values calculated using different methods. We demonstrate that previously reported apparent consistency between the ERF values derived from fixed sea surface temperature simulations and linear regression holds for most climate forcings, excluding black carbon (BC). When land adjustment is accounted for, however, the fixed sea surface temperature ERF values are generally 10–30&#37; larger than ERFs derived using linear regression across all forcing agents, with a much larger (~70–100&#37;) discrepancy for BC. Except for BC, this difference can be largely reduced by either using radiative kernel techniques or by exponential regression. Responses of clouds and their effects on shortwave radiation show the strongest variability in all experiments, limiting the application of regression-based ERF in small forcing simulations.

DOI： 10.1029/2018JD030188

Language：English   Publishing type：Research paper (scientific journal)  

©2019. The Authors. A comprehensive two-moment microphysics scheme is incorporated into the MIROC6-SPRINTARS general circulation model (GCM). The new scheme includes prognostic precipitation for both rain and snow and considers their radiative effects. To evaluate the impacts of applying different treatments of precipitation and the associated radiative effect, we perform climate simulations employing both the traditional diagnostic and new prognostic precipitation schemes, the latter also being tested with and without incorporating the radiative effect of snow. The prognostic precipitation, which maintains precipitation in the atmosphere across multiple time steps, models the ratio of accretion to autoconversion as being approximately an order of magnitude higher than that for the diagnostic scheme. Such changes in microphysical process rates tend to reduce the cloud water susceptibility as the autoconversion process is the only pathway through which aerosols can influence rain formation. The resultant anthropogenic aerosol effect is reduced by approximately 21&#37; in the prognostic precipitation scheme. Modifications to the microphysical process rates also change the vertical distribution of hydrometeors in the manner that increases the fractional occurrence of single-layered warm clouds by 38&#37;. The new scheme mitigates the excess of supercooled liquid water produced by the previous scheme and increases the total mass of ice hydrometeors. Both characteristics are consistent with CloudSat/CALIPSO retrievals. The radiative effect of snow is significant at both longwave and shortwave (6.4 and 5.1 W/m2 in absolute values, respectively) and can alter the precipitation fields via energetic controls on precipitation. These results suggest that the prognostic precipitation scheme, with its radiative effects incorporated, makes an indispensable contribution to improving the reliability of climate modeling.

DOI： 10.1029/2018MS001596

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-19-2441-2019

Language：English   Publishing type：Research paper (scientific journal)  

©2019. The Authors. Impacts of absorbing and scattering aerosols on global energy balance are investigated with a global climate model. A series of sensitivity experiments perturbing emissions of black carbon and sulfate aerosols individually is conducted with the model to explore how components of global energy budget change in response to the instantaneous radiative forcing due to the two types of aerosols. It is demonstrated how differing vertical structures of the instantaneous radiative forcing between the two aerosols induce distinctively different proportions of fast and slow climate responses through different energy redistribution into atmosphere and surface. These characteristics are quantified in the form of the whole picture of global energy budget perturbations normalized by the top-of-atmosphere instantaneous radiative forcing. The energy budget perturbation per “unit” instantaneous forcing thus quantified reveals relative magnitudes of changes to different component fluxes in restoring atmospheric and surface energy balances through fast and slow responses. The normalized picture then directly links the “initial forcing” to the eventual climate “responses,” thereby explaining how starkly different responses of the global-mean temperature and precipitation are induced by the two types of aerosols. The study underscores a critical need for better quantifications of the forcings' vertical structure and atmospheric rapid adjustment for reliable estimates of climatic impact of absorbing and scattering aerosols. In particular, cloud responses through the indirect and semidirect effects and the sensible heat decrease in response to stabilized atmosphere due to the black carbon heating are identified as key uncertain components in the global energy budget perturbation.

DOI： 10.1029/2018JD029808

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-018-37304-0

Language：English   Publishing type：Research paper (scientific journal)  

© 2018 The Author(s). Aerosols affect climate by modifying cloud properties through their role as cloud condensation nuclei or ice nuclei, called aerosol-cloud interactions. In most global climate models (GCMs), the aerosol-cloud interactions are represented by empirical parameterisations, in which the mass of cloud liquid water (LWP) is assumed to increase monotonically with increasing aerosol loading. Recent satellite observations, however, have yielded contradictory results: LWP can decrease with increasing aerosol loading. This difference implies that GCMs overestimate the aerosol effect, but the reasons for the difference are not obvious. Here, we reproduce satellite-observed LWP responses using a global simulation with explicit representations of cloud microphysics, instead of the parameterisations. Our analyses reveal that the decrease in LWP originates from the response of evaporation and condensation processes to aerosol perturbations, which are not represented in GCMs. The explicit representation of cloud microphysics in global scale modelling reduces the uncertainty of climate prediction.

DOI： 10.1038/s41467-018-03379-6

Language：English   Publishing type：Research paper (scientific journal)  

© 2018 American Meteorological Society. The response of the hydrological cycle to climate forcings can be understood within the atmospheric energy budget framework. In this study precipitation and energy budget responses to five forcing agents are analyzed using 10 climate models from the Precipitation Driver Response Model Intercomparison Project (PDRMIP). Precipitation changes are split into a forcing-dependent fast response and a temperature-driven hydrological sensitivity. Globally, when normalized by top-of-atmosphere (TOA) forcing, fast precipitation changes are most sensitive to strongly absorbing drivers (CO 2 , black carbon). However, over land fast precipitation changes are most sensitive to weakly absorbing drivers (sulfate, solar) and are linked to rapid circulation changes. Despite this, land-mean fast responses to CO 2 and black carbon exhibit more intermodel spread. Globally, the hydrological sensitivity is consistent across forcings, mainly associated with increased longwave cooling, which is highly correlated with intermodel spread. The land-mean hydrological sensitivity is weaker, consistent with limited moisture availability. The PDRMIP results are used to construct a simple model for land-mean and sea-mean precipitation change based on sea surface temperature change and TOA forcing. The model matches well with CMIP5 ensemble mean historical and future projections, and is used to understand the contributions of different drivers. During the twentieth century, temperature-driven intensification of land-mean precipitation has been masked by fast precipitation responses to anthropogenic sulfate and volcanic forcing, consistent with the small observed trend. However, as projected sulfate forcing decreases, and warming continues, land-mean precipitation is expected to increase more rapidly, and may become clearly observable by the mid-twenty-first century.

DOI： 10.1175/JCLI-D-17-0240.1

Language：English   Publishing type：Research paper (scientific journal)  

Globally, latent heating associated with a change in precipitation is balanced by changes to atmospheric radiative cooling and sensible heat fluxes. Both components can be altered by climate forcing mechanisms and through climate feedbacks, but the impacts of climate forcing and feedbacks on sensible heat fluxes have received much less attention. Here we show, using a range of climate modelling results, that changes in sensible heat are the dominant contributor to the present global-mean precipitation change since preindustrial time, because the radiative impact of forcings and feedbacks approximately compensate. The model results show a dissimilar influence on sensible heat and precipitation from various drivers of climate change. Due to its strong atmospheric absorption, black carbon is found to influence the sensible heat very differently compared to other aerosols and greenhouse gases. Our results indicate that this is likely caused by differences in the impact on the lower tropospheric stability.

DOI： 10.1038/s41467-018-04307-4

Language：English   Publishing type：Research paper (scientific journal)  

The effect of aerosols is one of many uncertain factors in projections of future climate. However, the behaviour of mineral dust aerosols (dust) can be investigated within the context of past climate change. The Last Glacial Maximum (LGM) is known to have had enhanced dust deposition in comparison with the present, especially over polar regions. Using the Model for Interdisciplinary Research on Climate Earth System Model (MIROC-ESM), we conducted a standard LGM experiment following the protocol of the Paleoclimate Modelling Intercomparison Project phase 3 and sensitivity experiments. We imposed glaciogenic dust on the standard LGM experiment and investigated the impacts of glaciogenic dust and non-glaciogenic dust on the LGM climate. Global mean radiative perturbations by glaciogenic and non-glaciogenic dust were both negative, consistent with previous studies. However, glaciogenic dust behaved differently in specific regions; e. g. it resulted in less cooling over the polar regions. One of the major reasons for reduced cooling is the ageing of snow or ice, which results in albedo reduction via high dust deposition, especially near sources of high glaciogenic dust emission. Although the net radiative perturbations in the lee of high glaciogenic dust provenances are negative, warming by the ageing of snow overcomes this radiative perturbation in the Northern Hemisphere. In contrast, the radiative perturbation due to high dust loading in the troposphere acts to warm the surface in areas surrounding Antarctica, primarily via the longwave aerosol-cloud interaction of dust, and it is likely the result of the greenhouse effect attributable to the enhanced cloud fraction in the upper troposphere. Although our analysis focused mainly on the results of experiments using the atmospheric part of the MIROC-ESM, we also conducted full MIROC-ESM experiments for an initial examination of the effect of glaciogenic dust on the oceanic general circulation module. A long-term trend of enhanced warming was observed in the Northern Hemisphere with increased glaciogenic dust; however, the level of warming around Antarctica remained almost unchanged, even after extended coupling with the ocean.

DOI： 10.5194/cp-14-1565-2018

Language：English   Publishing type：Research paper (scientific journal)  

©2018. The Authors. Rapid adjustments are responses to forcing agents that cause a perturbation to the top of atmosphere energy budget but are uncoupled to changes in surface warming. Different mechanisms are responsible for these adjustments for a variety of climate drivers. These remain to be quantified in detail. It is shown that rapid adjustments reduce the effective radiative forcing (ERF) of black carbon by half of the instantaneous forcing, but for CO2 forcing, rapid adjustments increase ERF. Competing tropospheric adjustments for CO2 forcing are individually significant but sum to zero, such that the ERF equals the stratospherically adjusted radiative forcing, but this is not true for other forcing agents. Additional experiments of increase in the solar constant and increase in CH4 are used to show that a key factor of the rapid adjustment for an individual climate driver is changes in temperature in the upper troposphere and lower stratosphere.

DOI： 10.1029/2018GL079826

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-18-15581-2018

Language：English   Publishing type：Research paper (scientific journal)  

©2018. The Authors. Different climate drivers influence precipitation in different ways. Here we use radiative kernels to understand the influence of rapid adjustment processes on precipitation in climate models. Rapid adjustments are generally triggered by the initial heating or cooling of the atmosphere from an external climate driver. For precipitation changes, rapid adjustments due to changes in temperature, water vapor, and clouds are most important. In this study we have investigated five climate drivers (CO2, CH4, solar irradiance, black carbon, and sulfate aerosols). The fast precipitation responses to a doubling of CO2 and a 10-fold increase in black carbon are found to be similar, despite very different instantaneous changes in the radiative cooling, individual rapid adjustments, and sensible heating. The model diversity in rapid adjustments is smaller for the experiment involving an increase in the solar irradiance compared to the other climate driver perturbations, and this is also seen in the precipitation changes.

DOI： 10.1029/2018GL079474

Language：English   Publishing type：Research paper (scientific journal)  

The global distribution of aerosol optical depth (AOD) is simulated using an aerosol transport model coupled to an atmospheric general circulation model with high spatial and temporal resolution. Daily representative AOD from model simulation is estimated after consideration of observation sampling in daytime (ground-based) and overpass time (satellite) after cloud masking. Large deviations in AOD are found after considering temporally inhomogeneous sampling, with positive differences over desert regions and negative differences over anthropogenic pollution and biomass burning regions. Mean difference in daily AOD of 5.33&#37; (standard deviation of 8.02&#37;), because of temporal inhomogeneous sampling, is identified based on observation time information from the Moderate-Resolution Imaging Spectroradiometer (MODIS). Relative differences in AOD of &gt
50&#37; and &gt
30&#37; were found in 7.9&#37; and 22.8&#37; of the data, respectively. Based on the observation time information from the AERONET, relative root mean square error (rRMSE) of AOD due to temporal inhomogeneous sampling is estimated to be 4.30–18.66&#37;. After correcting for temporal sampling inhomogeneity, the simulated global AOD was compared with AODs from MODIS and AERONET. The simulated AOD becomes lower than MODIS AOD because of emission and transport discrepancies related to dust, a limited accounting of nitrate processes, and limitation errors from MODIS AOD retrieval. A regional positive bias in SPRINTARS AOD was found in biomass burning regions, which is due to transport pattern errors related to the initial injection height of emissions. A weak correlation is found over the regions with multiple aerosol sources because of complex interactions of individual aerosol types.

DOI： 10.1016/j.atmosenv.2018.05.021

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-18-12223-2018

Language：English   Publishing type：Research paper (scientific journal)  

This study investigates the impact of anthropogenic aerosols on the atmospheric hydrological cycle over the tropical Asian monsoon region (South Asian, Southeast Asian, and western North Pacific monsoons), using a coupled atmosphere-ocean global climate model (CGCM), Model for Interdisciplinary Research on Climate-Earth System Models. Three-ensemble historical (HIST) and sensitivity (piAERO) experiments for the period 1985-2005 are conducted. The piAERO experiment is the same as HIST, but with anthropogenic aerosol emissions kept at preindustrial values. The results show that, as a whole, the Asian monsoon precipitation is reduced by the increase in aerosol loading during boreal summer and winter. This decrease in precipitation corresponds to a decrease in precipitable water due to the cooling in surface air temperature (SAT), mainly over adjacent oceans. The cooling is explained by the sum of the direct and indirect effects of aerosols. A modulation of the Walker circulation occurs, which can be explained by the east-west horizontal SAT gradient over the tropics due to the spatially heterogeneous increase in aerosols. Concurrent with the modulation of the Walker circulation, the anomalous descending motions over the tropical Asian monsoon region are consistent with the decrease in precipitation. In addition, the changes in local Hadley circulation (or a shift of the inter-tropical convergence zone) are unclear over the Asian monsoon region and thus cannot explain the decrease in precipitation. Moreover, the detailed spatial pattern of the response of the atmospheric hydrological cycle over the Asian monsoon region has distinct seasonality. Interestingly, signals are distinct in regions where tropical disturbance activity is vigorous during both boreal summer and winter. However, uncertainties regarding aerosol-cloud-precipitation interactions in current climate models and internal variability in the climate models may have affected the results.

DOI： 10.1186/s40645-018-0197-2

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-18-10497-2018

Language：English   Publishing type：Research paper (scientific journal)  

Atmospheric aerosols such as sulfate and black carbon (BC) generate inhomogeneous radiative forcing and can affect precipitation in distinct ways compared to greenhouse gases (GHGs). Their regional effects on the atmospheric energy budget and circulation can be important for understanding and predicting global and regional precipitation changes, which act on top of the background GHG-induced hydrological changes. Under the framework of the Precipitation Driver Response Model Intercomparison Project (PDRMIP), multiple models were used for the first time to simulate the influence of regional (Asian and European) sulfate and BC forcing on global and regional precipitation. The results show that, as in the case of global aerosol forcing, the global fast precipitation response to regional aerosol forcing scales with global atmospheric absorption, and the slow precipitation response scales with global surface temperature response. Asian sulfate aerosols appear to be a stronger driver of global temperature and precipitation change compared to European aerosols, but when the responses are normalized by unit radiative forcing or by aerosol burden change, the picture reverses, with European aerosols being more efficient in driving global change. The global apparent hydrological sensitivities of these regional forcing experiments are again consistent with those for corresponding global aerosol forcings found in the literature. However, the regional responses and regional apparent hydrological sensitivities do not align with the corresponding global values. Through a holistic approach involving analysis of the energy budget combined with exploring changes in atmospheric dynamics, we provide a framework for explaining the global and regional precipitation responses to regional aerosol forcing.

DOI： 10.1175/JCLI-D-17-0439.1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-18-8727-2018

Language：English   Publishing type：Research paper (scientific journal)  

Atmospheric aerosols and greenhouse gases affect cloud properties, radiative balance and, thus, the hydrological cycle. Observations show that precipitation has decreased in the Mediterranean since the beginning of the 20th century, and many studies have investigated possible mechanisms. So far, however, the effects of aerosol forcing on Mediterranean precipitation remain largely unknown. Here we compare the modeled dynamical response of Mediterranean precipitation to individual forcing agents in a set of global climate models (GCMs). Our analyses show that both greenhouse gases and aerosols can cause drying in the Mediterranean and that precipitation is more sensitive to black carbon (BC) forcing than to well-mixed greenhouse gases (WMGHGs) or sulfate aerosol. In addition to local heating, BC appears to reduce precipitation by causing an enhanced positive sea level pressure (SLP) pattern similar to the North Atlantic Oscillation-Arctic Oscillation, characterized by higher SLP at midlatitudes and lower SLP at high latitudes. WMGHGs cause a similar SLP change, and both are associated with a northward diversion of the jet stream and storm tracks, reducing precipitation in the Mediterranean while increasing precipitation in northern Europe. Though the applied forcings were much larger, if forcings are scaled to those of the historical period of 1901-2010, roughly one-third (31±17g&#37;) of the precipitation decrease would be attributable to global BC forcing with the remainder largely attributable to WMGHGs, whereas global scattering sulfate aerosols would have negligible impacts. Aerosol-cloud interactions appear to have minimal impacts on Mediterranean precipitation in these models, at least in part because many simulations did not fully include such processes
these merit further study. The findings from this study suggest that future BC and WMGHG emissions may significantly affect regional water resources, agricultural practices, ecosystems and the economy in the Mediterranean region.

DOI： 10.5194/acp-18-8439-2018

Language：English   Publishing type：Research paper (scientific journal)  

This study uses multi-model ensemble results of 11 models from the second phase of Task Force Hemispheric Transport of Air Pollution (HTAP II) to calculate the global sulfur (S) and nitrogen (N) deposition in 2010. Modeled wet deposition is evaluated with observation networks in North America, Europe and East Asia. The modeled results agree well with observations, with 76-83&#37; of stations being predicted within ±50&#37; of observations. The models underestimate SO42-, NO3 - and NH4 + wet depositions in some European and East Asian stations but overestimate NO3 - wet deposition in the eastern United States. Intercomparison with previous projects (PhotoComp, ACCMIP and HTAP I) shows that HTPA II has considerably improved the estimation of deposition at European and East Asian stations. Modeled dry deposition is generally higher than the q inferential/q data calculated by observed concentration and modeled velocity in North America, but the inferential data have high uncertainty, too. The global S deposition is 84Tg(S) in 2010, with 49&#37; in continental regions and 51&#37; in the ocean (19&#37; of which coastal). The global N deposition consists of 59Tg(N) oxidized nitrogen (NOy) deposition and 64Tg(N) reduced nitrogen (NHx) deposition in 2010. About 65&#37; of N is deposited in continental regions, and 35&#37; in the ocean (15&#37; of which coastal). The estimated outflow of pollution from land to ocean is about 4Tg(S) for S deposition and 18Tg(N) for N deposition. Comparing our results to the results in 2001 from HTAP I, we find that the global distributions of S and N deposition have changed considerably during the last 10 years. The global S deposition decreases 2Tg(S) (3&#37;) from 2001 to 2010, with significant decreases in Europe (5Tg(S) and 55&#37;), North America (3Tg(S) and 29&#37;) and Russia (2Tg(S) and 26&#37;), and increases in South Asia (2Tg(S) and 42&#37;) and the Middle East (1Tg(S) and 44&#37;). The global N deposition increases by 7Tg(N) (6&#37;), mainly contributed by South Asia (5Tg(N) and 39&#37;), East Asia (4Tg(N) and 21&#37;) and Southeast Asia (2Tg(N) and 21&#37;). The NHx deposition increases with no control policy on NH3 emission in North America. On the other hand, NOy deposition has started to dominate in East Asia (especially China) due to boosted NOx emission.

DOI： 10.5194/acp-18-6847-2018

Language：English   Publishing type：Research paper (scientific journal)  

Future projections of east Amazonian precipitation indicate drying, but they are uncertain and poorly understood. In this study we analyze the Amazonian precipitation response to individual atmospheric forcings using a number of global climate models. Black carbon is found to drive reduced precipitation over the Amazon due to temperature-driven circulation changes, but the magnitude is uncertain. CO2 drives reductions in precipitation concentrated in the east, mainly due to a robustly negative, but highly variable in magnitude, fast response. We find that the physiological effect of CO2 on plant stomata is the dominant driver of the fast response due to reduced latent heating and also contributes to the large model spread. Using a simple model, we show that CO2 physiological effects dominate future multimodel mean precipitation projections over the Amazon. However, in individual models temperature-driven changes can be large, but due to little agreement, they largely cancel out in the model mean.

DOI： 10.1002/2017GL076520

Language：Japanese   Publishing type：Research paper (scientific journal)  

IMPACT OF SHORT-LIVED CLIMATE POLLUTANTS ON TERRESTRIAL WATER CIRCULATION
&nbsp;In this study, we investigated the impact of black carbon, BC, as one of Short-Lived Climate Pollutants or SLCP on terrestrial water circulation, in addition to that of sulfur dioxide, SO₂, with the terrestrial offline simulation framework. Results are shown as follows: 1) Both BC and SO₂ decrease the global precipitation whereas decrease in runoff is relatively large with BC. 2) However, spatial distributions of the change in precipitation and runoff are quite patchy and different in BC and SO₂. 3) Decrease in BC emission would relax the global water stress. 4) No matter decrease or increase, change in BC or SO₂ emission would cuase increase the risk of severe flood exposure.

DOI： 10.2208/jscejhe.74.I_217

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41612-017-0005-5

Language：English   Publishing type：Research paper (scientific journal)  

We investigate the climate response to increased concentrations of black carbon (BC), as part of the Precipitation Driver Response Model Intercomparison Project (PDRMIP). A tenfold increase in BC is simulated by nine global coupled-climate models, producing a model median effective radiative forcing of 0.82 (ranging from 0.41 to 2.91) Wm(-2), and a warming of 0.67 (0.16 to 1.66) K globally and 1.24 (0.26 to 4.31) K in the Arctic. A strong positive instantaneous radiative forcing (median of 2.10 Wm(-2) based on five of the models) is countered by negative rapid adjustments (-0.64 Wm(-2) for the same five models), which dampen the total surface temperature signal. Unlike other drivers of climate change, the response of temperature and cloud profiles to the BC forcing is dominated by rapid adjustments. Low-level cloud amounts increase for all models, while higher-level clouds are diminished. The rapid temperature response is particularly strong above 400 h Pa, where increased atmospheric stabilization and reduced cloud cover contrast the response pattern of the other drivers. In conclusion, we find that this substantial increase in BC concentrations does have considerable impacts on important aspects of the climate system. However, some of these effects tend to offset one another, leaving a relatively small median global warming of 0.47 K per Wm(-2)-about 20&#37; lower than the response to a doubling of CO2. Translating the tenfold increase in BC to the present-day impact of anthropogenic BC (given the emissions used in this work) would leave a warming of merely 0.07 K.

DOI： 10.1002/2017JD027326

Language：English   Publishing type：Research paper (scientific journal)  

Atmospheric aerosols from anthropogenic and natural sources reach the polar regions through long-range transport and affect the local radiation balance. Such transport is, however, poorly constrained in present-day global climate models, and few multi-model evaluations of polar anthropogenic aerosol radiative forcing exist. Here we compare the aerosol optical depth (AOD) at 550 nm from simulations with 16 global aerosol models from the AeroCom Phase II model intercomparison project with available observations at both poles. We show that the annual mean multi-model median is representative of the observations in Arctic, but that the intermodel spread is large. We also document the geographical distribution and seasonal cycle of the AOD for the individual aerosol species: black carbon (BC) from fossil fuel and biomass burning, sulfate, organic aerosols (OAs), dust, and sea-salt. For a subset of models that represent nitrate and secondary organic aerosols (SOAs), we document the role of these aerosols at high latitudes.
The seasonal dependence of natural and anthropogenic aerosols differs with natural aerosols peaking in winter (sea-salt) and spring (dust), whereas AOD from anthropogenic aerosols peaks in late spring and summer. The models produce a median annual mean AOD of 0.07 in the Arctic (defined here as north of 60 degrees N). The models also predict a noteworthy aerosol transport to the Antarctic (south of 70 degrees S) with a resulting AOD varying between 0.01 and 0.02. The models have estimated the shortwave anthropogenic radiative forcing contributions to the direct aerosol effect (DAE) associated with BC and OA from fossil fuel and biofuel (FF), sulfate, SOAs, nitrate, and biomass burning from BC and OA emissions combined. The Arctic modelled annual mean DAE is slightly negative ( -0.12Wm(-2)), dominated by a positive BC FF DAE in spring and a negative sulfate DAE in summer. The Antarctic DAE is governed by BC FF. We perform sensitivity experiments with one of the AeroCom models (GISS modelE) to investigate how regional emissions of BC and sulfate and the lifetime of BC influence the Arctic and Antarctic AOD. A doubling of emissions in eastern Asia results in a 33&#37; increase in Arctic AOD of BC. A doubling of the BC lifetime results in a 39&#37; increase in Arctic AOD of BC. However, these radical changes still fall within the AeroCom model range.

DOI： 10.5194/acp-17-12197-2017

Language：English   Publishing type：Research paper (scientific journal)  

Ground-level ozone and fine particulate matter (PM2.5) are associated with premature human mortality(1-4); their future concentrations depend on changes in emissions, which dominate the near-term(5), and on climate change(6,7). Previous global studies of the air-quality-related health effects of future climate change(8,9) used single atmospheric models. However, in related studies, mortality results differ among models(10-12). Here we use an ensemble of global chemistry-climate models(13) to show that premature mortality from changes in air pollution attributable to climate change, under the high greenhouse gas scenario RCP8.5 (ref. 14), is probably positive. We estimate 3,340 (-30,300 to 47,100) ozone-related deaths in 2030, relative to 2000 climate, and 43,600 (-195,000 to 237,000) in 2100 (14&#37; of the increase in global ozone-related mortality). For PM2.5, we estimate 55,600 (-34,300 to 164,000) deaths in 2030 and 215,000 (-76,100 to 595,000) in 2100 (countering by 16&#37; the global decrease in PM2.5-related mortality). Premature mortality attributable to climate change is estimated to be positive in all regions except Africa, and is greatest in India and East Asia. Most individual models yield increased mortality from climate change, but some yield decreases, suggesting caution in interpreting results from a single model. Climate change mitigation is likely to reduce air-pollution-related mortality.

DOI： 10.1038/NCLIMATE3354

Language：English   Publishing type：Research paper (scientific journal)  

This study examines the influence of the Caspian Sea-Hindu Kush Index (CasHKI) on local and synoptic meteorology as well as on dust emissions over southwest (SW) Asia by means of National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP-NCAR) re-analysed mean sea-level pressure (MSLP), geopotential height at 700 hPa and surface meridional wind, along with meteorological data at Zabol, east Iran and Meteosat/Infrared Difference Dust Index (IDDI) retrievals. The analysis focuses on the summer period (June to September) of 2000-2014 and the winter period (November to March) of 1963-2014. The CasHKI values are mostly controlled by the MSLP anomalies over the Caspian Sea (CS) domain, varying from approximately -25 to +35 hPa in winter and from approximately -10 to +14 hPa in summer, but without a clear annual pattern. The CasHKI values are classified into four modes for each month depending on their intensity. In the summer months, the high CasHKI mode is associated with enhanced MSLP over central Asia and deepening of the Indo-Pakistan thermal low associated with the Indian summer monsoon. At 700-hPa level, the high CasHKI mode shows an enhancement of the Arabian ridge, expanding it to the north over Iran and the CS, with a concurrent strengthening of the Indian trough, leading to intensification of northerly winds along east Iran. This results in significant increase in dust activity over SWAsia, which is also apparent in the winter months. Furthermore, the intensification of the northerly flow associated with the high CasHKI modes drops the temperature and increases the relative humidity over Zabol, especially during winter. The SPRINTARS-model simulations also show increased dust emissions and concentrations for the high CasHKI values, confirming that the CasHKI variations modulate the dust activity over SW Asia throughout the year.

DOI： 10.1002/joc.5053

Language：English   Publishing type：Research paper (scientific journal)  

PDRMIP investigates the role of various drivers of climate change for mean and extreme precipitation changes based on multiple climate model output and energy budget analyses.

DOI： 10.1175/BAMS-D-16-0019.1

Language：English   Publishing type：Research paper (scientific journal)  

Much of the uncertainty in estimates of the anthropogenic forcing of climate change comes from uncertainties in the instantaneous effect of aerosols on cloud albedo, known as the Twomey effect or the radiative forcing from aerosol-cloud interactions (RFaci), a component of the total or effective radiative forcing. Because aerosols serving as cloud condensation nuclei can have a strong influence on the cloud droplet number concentration (Nd), previous studies have used the sensitivity of the Nd to aerosol properties as a constraint on the strength of the RFaci. However, recent studies have suggested that relationships between aerosol and cloud properties in the present-day climate may not be suitable for determining the sensitivity of the Nd to anthropogenic aerosol perturbations. Using an ensemble of global aerosol-climate models, this study demonstrates how joint histograms between Nd and aerosol properties can account for many of the issues raised by previous studies. It shows that if the anthropogenic contribution to the aerosol is known, the RFaci can be diagnosed to within 20&#37; of its actual value. The accuracy of different aerosol proxies for diagnosing the RFaci is investigated, confirming that using the aerosol optical depth significantly underestimates the strength of the aerosol-cloud interactions in satellite data.

DOI： 10.1073/pnas.1617765114

Language：English   Publishing type：Research paper (scientific journal)  

The sensitivities of oxygen dimer (O-4) slant column densities (SCDs) were examined by applying temperature-dependent O-4 cross sections using the radiative transfer model (RTM) calculation with the linearized pseudo-spherical vector discrete ordinate radiative transfer model. For the sensitivity study, we used a newly developed cross section database in place of the database used in the operational algorithm. Newly investigated O-4 cross section databases for 203 K and 293 K were used for the radiance simulation by interpolating temperature for each atmospheric layer based on the vertical profile of standard atmosphere in the RTM. The effect of the temperature-dependent cross sections was a significant O-4 SCD increase of 8.3&#37; with dependence on satellite and solar viewing geometries. Furthermore, the O-4 SCD generally increased by an estimated 3.9&#37; based on the observation geometries of the Ozone Monitoring Instrument. For the long-term comparison, the O-4 SCD estimated from the temperature-dependent cross sections corrects 20&#37; of the total underestimation of O-4 SCD between the observation and simulation. Although the surface pressure variation and background aerosol effect also correct the O-4 SCD discrepancy, the effect of temperature-dependent cross sections was more important than the effects of surface pressure variation and background aerosols. Therefore, temperature dependence of the cross section in the RTM calculation is essential for the accurate simulation of O-4 SCD. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2016.12.020

Language：English   Publishing type：Research paper (scientific journal)  

Over the past few decades, the geographical distribution of emissions of substances that alter the atmospheric energy balance has changed due to economic growth and air pollution regulations. Here, we show the resulting changes to aerosol and ozone abundances and their radiative forcing using recently updated emission data for the period 1990-2015, as simulated by seven global atmospheric composition models. The models broadly reproduce large-scale changes in surface aerosol and ozone based on observations (e.g. -1 to -3&#37; yr(-1) in aerosols over the USA and Europe). The global mean radiative forcing due to ozone and aerosol changes over the 1990-2015 period increased by +0.17 +/- 0.08 W m(-2), with approximately one-third due to ozone. This increase is more strongly positive than that reported in IPCC AR5. The main reasons for the increased positive radiative forcing of aerosols over this period are the substantial reduction of global mean SO2 emissions, which is stronger in the new emission inventory compared to that used in the IPCC analysis, and higher black carbon emissions.

DOI： 10.5194/acp-17-2709-2017

Language：English   Publishing type：Research paper (scientific journal)  

In this study, a new method is proposed for the depiction of the atmospheric transportation of the Cs-137 emitted from the Fukushima Daiichi Nuclear Power Station accident. This method employs a combination of the results of two aerosol model ensembles and the hourly observed atmospheric Cs-137 concentration at surface level during 14-23 March 2011 at 90 sites in the suspended particulate matter monitoring network. The new method elucidates accurate transport routes and the distribution of the surface-level atmospheric Cs-137 relevant to eight plume events that were previously identified. The model ensemble simulates the main features of the observed distribution of surface-level atmospheric Cs-137. However, significant differences were found in some cases, and this suggests the need to improve the modeling of the emission scenario, plume height, wet deposition process, and plume propagation in the Abukuma Mountain region. The contributions of these error sources differ in the early and dissipating phases of each event, depending on the meteorological conditions.

DOI： 10.1186/s40645-017-0117-x

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Language：English   Publishing type：Research paper (scientific journal)  

The increasing severity of droughts/floods and worsening air quality from increasing aerosols in Asia monsoon regions are the two gravest threats facing over 60&#37; of the world population living in Asian monsoon regions. These dual threats have fueled a large body of research in the last decade on the roles of aerosols in impacting Asian monsoon weather and climate. This paper provides a comprehensive review of studies on Asian aerosols, monsoons, and their interactions. The Asian monsoon region is a primary source of emissions of diverse species of aerosols from both anthropogenic and natural origins. The distributions of aerosol loading are strongly influenced by distinct weather and climatic regimes, which are, in turn, modulated by aerosol effects. On a continental scale, aerosols reduce surface insolation and weaken the land-ocean thermal contrast, thus inhibiting the development of monsoons. Locally, aerosol radiative effects alter the thermodynamic stability and convective potential of the lower atmosphere leading to reduced temperatures, increased atmospheric stability, and weakened wind and atmospheric circulations. The atmospheric thermodynamic state, which determines the formation of clouds, convection, and precipitation, may also be altered by aerosols serving as cloud condensation nuclei or ice nuclei. Absorbing aerosols such as black carbon and desert dust in Asian monsoon regions may also induce dynamical feedback processes, leading to a strengthening of the early monsoon and affecting the subsequent evolution of the monsoon. Many mechanisms have been put forth regarding how aerosols modulate the amplitude, frequency, intensity, and phase of different monsoon climate variables. A wide range of theoretical, observational, and modeling findings on the Asian monsoon, aerosols, and their interactions are synthesized. A new paradigm is proposed on investigating aerosol-monsoon interactions, in which natural aerosols such as desert dust, black carbon from biomass burning, and biogenic aerosols from vegetation are considered integral components of an intrinsic aerosol-monsoon climate system, subject to external forcing of global warming, anthropogenic aerosols, and land use and change. Future research on aerosol-monsoon interactions calls for an integrated approach and international collaborations based on long-term sustained observations, process measurements, and improved models, as well as using observations to constrain model simulations and projections.

DOI： 10.1002/2015RG000500

Language：English   Publishing type：Research paper (scientific journal)  

Aerosol-cloud interactions are one of the most uncertain processes in climate models due to their nonlinear complexity. A key complexity arises from the possibility that clouds can respond to perturbed aerosols in two opposite ways, as characterized by the traditional "cloud lifetime" hypothesis and more recent "buffered system" hypothesis. Their importance in climate simulations remains poorly understood. Here we investigate the response of the liquid water path (LWP) to aerosol perturbations for warm clouds from the perspective of general circulation model (GCM) and A-Train remote sensing, through process-oriented model evaluations. A systematic difference is found in the LWP response between the model results and observations. The model results indicate a near-global uniform increase of LWP with increasing aerosol loading, while the sign of the response of the LWP from the A-Train varies from region to region. The satellite-observed response of the LWP is closely related to meteorological and/or macrophysical factors, in addition to the microphysics. The model does not reproduce this variability of cloud susceptibility (i.e., sensitivity of LWP to perturbed aerosols) because the parameterization of the autoconversion process assumes only suppression of rain formation in response to increased cloud droplet number, and does not consider macrophysical aspects that serve as a mechanism for the negative responses of the LWP via enhancements of evaporation and precipitation. Model biases are also found in the precipitation microphysics, which suggests that the model generates rainwater readily even when little cloud water is present. This essentially causes projections of unrealistically frequent and light rain, with high cloud susceptibilities to aerosol perturbations.

DOI： 10.5194/acp-16-15413-2016

Language：English   Publishing type：Research paper (scientific journal)  

In the Hemispheric Transport of Air Pollution Phase 2 (HTAP2) exercise, a range of global atmospheric general circulation and chemical transport models performed coordinated perturbation experiments with 20&#37; reductions in emissions of anthropogenic aerosols, or aerosol precursors, in a number of source regions. Here, we compare the resulting changes in the atmospheric load and vertically resolved profiles of black carbon (BC), organic aerosols (OA) and sulfate (SO4) from 10 models that include treatment of aerosols. We use a set of temporally, horizontally and vertically resolved profiles of aerosol forcing efficiency (AFE) to estimate the impact of emission changes in six major source regions on global radiative forcing (RF) pertaining to the direct aerosol effect, finding values between. 51.9 and 210.8 mW m(-2) Tg(-1) for BC, between -2.4 and -17.9 mW m(-2) Tg(-1) for OA and between -3.6 and -10.3 W m(-2) Tg(-1) for SO4. In most cases, the local influence dominates, but results show that mitigations in south and east Asia have substantial impacts on the radiative budget in all investigated receptor regions, especially for BC. In Russia and the Middle East, more than 80 &#37; of the forcing for BC and OA is due to extra-regional emission reductions. Similarly, for North America, BC emissions control in east Asia is found to be more important than domestic mitigations, which is consistent with previous findings. Comparing fully resolved RF calculations to RF estimates based on vertically averaged AFE profiles allows us to quantify the importance of vertical resolution to RF estimates. We find that locally in the source regions, a 20&#37; emission reduction strengthens the radiative forcing associated with SO4 by 25&#37; when including the vertical dimension, as the AFE for SO4 is strongest near the surface. Conversely, the local RF from BC weakens by 37&#37; since BC AFE is low close to the ground. The fraction of BC direct effect forcing attributable to intercontinental transport, on the other hand, is enhanced by one-third when accounting for the vertical aspect, because long-range transport primarily leads to aerosol changes at high altitudes, where the BC AFE is strong. While the surface temperature response may vary with the altitude of aerosol change, the analysis in the present study is not extended to estimates of temperature or precipitation changes.

DOI： 10.5194/acp-16-13579-2016

Language：English   Publishing type：Research paper (scientific journal)  

Ambient air pollution from ground-level ozone and fine particulate matter (PM2.5) is associated with premature mortality. Future concentrations of these air pollutants will be driven by natural and anthropogenic emissions and by climate change. Using anthropogenic and biomass burning emissions projected in the four Representative Concentration Pathway scenarios (RCPs), the ACCMIP ensemble of chemistry-climate models simulated future concentrations of ozone and PM2.5 at selected decades between 2000 and 2100. We use output from the ACCMIP ensemble, together with projections of future population and baseline mortality rates, to quantify the human premature mortality impacts of future ambient air pollution. Future air-pollution-related premature mortality in 2030, 2050 and 2100 is estimated for each scenario and for each model using a health impact function based on changes in concentrations of ozone and PM2.5 relative to 2000 and projected future population and baseline mortality rates. Additionally, the global mortality burden of ozone and PM2.5 in 2000 and each future period is estimated relative to 1850 concentrations, using present-day and future population and baseline mortality rates. The change in future ozone concentrations relative to 2000 is associated with excess global premature mortality in some scenarios/periods, particularly in RCP8.5 in 2100 (316 thousand deaths year(-1)), likely driven by the large increase in methane emissions and by the net effect of climate change projected in this scenario, but it leads to considerable avoided premature mortality for the three other RCPs. However, the global mortality burden of ozone markedly increases from 382 000 (121 000 to 728 000) deaths year(-1) in 2000 to between 1.09 and 2.36 million deaths year(-1) in 2100, across RCPs, mostly due to the effect of increases in population and baseline mortality rates. PM2.5 concentrations decrease relative to 2000 in all scenarios, due to projected reductions in emissions, and are associated with avoided premature mortality, particularly in 2100: between -2.39 and -1.31 million deaths year(-1) for the four RCPs. The global mortality burden of PM2.5 is estimated to decrease from 1.70 (1.30 to 2.10) million deaths year 1 in 2000 to between 0.95 and 1.55 million deaths year 1 in 2100 for the four RCPs due to the combined effect of decreases in PM2.5 concentrations and changes in population and baseline mortality rates. Trends in future air-pollution-related mortality vary regionally across scenarios, reflecting assumptions for economic growth and air pollution control specific to each RCP and region. Mortality estimates differ among chemistry-climate models due to differences in simulated pollutant concentrations, which is the greatest contributor to overall mortality uncertainty for most cases assessed here, supporting the use of model ensembles to characterize uncertainty. Increases in exposed population and baseline mortality rates of respiratory diseases magnify the impact on premature mortality of changes in future air pollutant concentrations and explain why the future global mortality burden of air pollution can exceed the current burden, even where air pollutant concentrations decrease.

DOI： 10.5194/acp-16-9847-2016

Language：English   Publishing type：Research paper (scientific journal)  

The ability of 11 models in simulating the aerosol vertical distribution from regional to global scales, as part of the second phase of the AeroCom model intercomparison initiative (AeroCom II), is assessed and compared to results of the first phase. The evaluation is performed using a global monthly gridded data set of aerosol extinction profiles built for this purpose from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Layer Product 3.01. Results over 12 subcontinental regions show that five models improved, whereas three degraded in reproducing the interregional variability in Z(alpha 0-6 km), the mean extinction height diagnostic, as computed from the CALIOP aerosol profiles over the 0-6 km altitude range for each studied region and season. While the models' performance remains highly variable, the simulation of the timing of the Z(alpha 0-6 km) peak season has also improved for all but two models from AeroCom Phase I to Phase II. The biases in Z(alpha 0-6 km) are smaller in all regions except Central Atlantic, East Asia, and North and South Africa. Most of the models now underestimate Z(alpha 0-6 km) over land, notably in the dust and biomass burning regions in Asia and Africa. At global scale, the AeroCom II models better reproduce the Z(alpha 0-6 km) latitudinal variability over ocean than over land. Hypotheses for the performance and evolution of the individual models and for the intermodel diversity are discussed. We also provide an analysis of the CALIOP limitations and uncertainties contributing to the differences between the simulations and observations.

DOI： 10.1002/2015JD024639

Language：English   Publishing type：Research paper (scientific journal)  

Black carbon aerosol (BCA) in the Arctic has profound impacts on the global climate system through radiation processes. Despite its enormous impacts, current global scale models, powerful tools for estimating overall impact, tend to underestimate the levels of BCA in the Arctic over several seasons. Using a global aerosol transport simulation with a horizontal grid resolution of 3.5 km, we determined that a higher resolution significantly reduced the underestimation of BCA levels in the Arctic, mainly due to an enhancement of the representation of low-pressure and frontal systems. The BCA mass loading in the Arctic simulated with 3.5-km grid resolution was 4.2-times larger than that simulated with coarse (56-km) grid resolution. Our results also indicated that grid convergence had not occurred on both the contrast between the cloud/cloud free areas and the poleward BCA mass flux, despite the use of the 3.5-km grid resolution. These results suggest that a global aerosol transport simulation using kilometre-order or finer grid resolution is required for more accurate estimation of the distribution of pollutants in the Arctic.

DOI： 10.1038/srep26561

Language：English   Publishing type：Research paper (scientific journal)  

The ability of 11 models in simulating the aerosol vertical distribution from regional to global scales, as part of the second phase of the AeroCom model intercomparison initiative (AeroCom II), is assessed and compared to results of the first phase. The evaluation is performed using a global monthly gridded data set of aerosol extinction profiles built for this purpose from the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Layer Product 3.01. Results over 12 subcontinental regions show that five models improved, whereas three degraded in reproducing the interregional variability in Zα0-6 km, the mean extinction height diagnostic, as computed from the CALIOP aerosol profiles over the 0-6 km altitude range for each studied region and season. While the models’ performance remains highly variable, the simulation of the timing of the Zα0-6 km peak season has also improved for all but two models from AeroCom Phase I to Phase II. The biases in Zα0-6 kmare smaller in all regions except Central Atlantic, East Asia, and North and South Africa. Most of the models now underestimate Zα0-6 km over land, notably in the dust and biomass burning regions in Asia and Africa. At global scale, the AeroCom II models better reproduce the Zα0-6 km latitudinal variability over ocean than over land. Hypotheses for the performance and evolution of the individual models and for the intermodel diversity are discussed. We also provide an analysis of the CALIOP limitations and uncertainties contributing to the differences between the simulations and observations.

DOI： 10.1002/2015JD024639

Language：English   Publishing type：Research paper (scientific journal)  

A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing.

DOI： 10.1073/pnas.1514036113

Language：English   Publishing type：Research paper (scientific journal)  

Aerosol properties above clouds have been retrieved over the South East Atlantic Ocean during the fire season 2006 using satellite observations from POLDER (Polarization and Directionality of Earth Reflectances). From June to October, POLDER has observed a mean Above-Cloud Aerosol Optical Thickness (ACAOT) of 0.28 and a mean Above-Clouds Single Scattering Albedo (ACSSA) of 0.87 at 550 nm. These results have been used to evaluate the simulation of aerosols above clouds in five Aerosol Comparisons between Observations and Models (Goddard Chemistry Aerosol Radiation and Transport (GOCART), Hadley Centre Global Environmental Model 3 (HadGEM3), European Centre Hamburg Model 5-Hamburg Aerosol Module 2 (ECHAM5-HAM2), Oslo-Chemical Transport Model 2 (OsloCTM2), and Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS)). Most models do not reproduce the observed large aerosol load episodes. The comparison highlights the importance of the injection height and the vertical transport parameterizations to simulate the large ACAOT observed by POLDER. Furthermore, POLDER ACSSA is best reproduced by models with a high imaginary part of black carbon refractive index, in accordance with recent recommendations.

DOI： 10.1002/2016GL068222

Language：English   Publishing type：Research paper (scientific journal)  

Aerosol-cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity (omega(500)), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strong large-scale ascent (omega(500)aEuro-aEuro parts per thousand < aEuro-a'25 hPa day(-1)) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is close to that in subsidence regimes, which indicates that regimes with strong large-scale ascent are as important as stratocumulus regimes in studying AIE. It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm day(-1)) contributes the most to the total aerosol indirect forcing (from 64 to nearly 100 &#37;). Results show that the uncertainty in AIE is even larger within specific dynamical regimes compared to the uncertainty in its global mean values, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes.

DOI： 10.5194/acp-16-2765-2016

Language：English   Publishing type：Research paper (scientific journal)  

Precipitation is expected to respond differently to various drivers of anthropogenic climate change. We present the first results from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP), where nine global climate models have perturbed CO2, CH4, black carbon, sulfate, and solar insolation. We divide the resulting changes to global mean and regional precipitation into fast responses that scale with changes in atmospheric absorption and slow responses scaling with surface temperature change. While the overall features are broadly similar between models, we find significant regional intermodel variability, especially over land. Black carbon stands out as a component that may cause significant model diversity in predicted precipitation change. Processes linked to atmospheric absorption are less consistently modeled than those linked to top-of-atmosphere radiative forcing. We identify a number of land regions where the model ensemble consistently predicts that fast precipitation responses to climate perturbations dominate over the slow, temperature-driven responses.

DOI： 10.1002/2016GL068064

Language：English   Publishing type：Research paper (scientific journal)  

This work investigates the modulation in dust activity over southwest (SW) Asia attributed to changes in the mean sea level pressure (MSLP) between the Caspian Sea (CS) and Hindu Kush (HK) during the summer months (June-July-August-September,BAS) of the period 2000-2014. The MSLP anomalies obtained via NCEP/NCAR re-analysis are evaluated via a new climatology index, the Caspian Sea-Hindu Kush Index (CasHKI), which is defined as CasHICI = MSLPanom.CS - MSLPanom.HK, over specific domains taken over the CS and HK. The changes in CasHKI intensity are examined against dust activity and rainfall distributions over south Asia. The satellite remote sensing (Meteosat, OMI, MODIS) analyses show that high CasHKI values corresponding to enhanced pressure gradient between the CS and the HK, are associated with intensification of northerly winds, increased dust emissions and transportation over SW Asia and north Arabian Sea. In contrast, variations in CasHIC intensity do not seem to have a significant effect on the Indian summer monsoon. Only a slight decrease of precipitation over the southern Indian peninsula and the neighboring oceanic areas and an increase of precipitation along the Ganges Basin and Himalayan range are found to be related to high CasHKI values. Model (MIROC-SPRINTARS) simulations of dust concentration and dust AOD (Aerosol Optical Depth) over SW Asia are consistent with the satellite observations, highlighting for the first time the modulation of the SW Asian dust activity by CasHKI. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gloplacha.2015.12.011

Language：English   Publishing type：Research paper (scientific journal)  

The vertical profile of aerosol is important for its radiative effects, but weakly constrained by observations on the global scale, and highly variable among different models. To investigate the controlling factors in one particular model, we investigate the effects of individual processes in HadGEM3-UKCA and compare the resulting diversity of aerosol vertical profiles with the inter-model diversity from the AeroCom Phase II control experiment.
In this way we show that (in this model at least) the vertical profile is controlled by a relatively small number of processes, although these vary among aerosol components and particle sizes. We also show that sufficiently coarse variations in these processes can produce a similar diversity to that among different models in terms of the global-mean profile and, to a lesser extent, the zonal-mean vertical position. However, there are features of certain models' profiles that cannot be reproduced, suggesting the influence of further structural differences between models.
In HadGEM3-UKCA, convective transport is found to be very important in controlling the vertical profile of all aerosol components by mass. In-cloud scavenging is very important for all except mineral dust. Growth by condensation is important for sulfate and carbonaceous aerosol (along with aqueous oxidation for the former and ageing by soluble material for the latter). The vertical extent of biomass-burning emissions into the free troposphere is also important for the profile of carbonaceous aerosol. Boundary-layer mixing plays a dominant role for sea salt and mineral dust, which are emitted only from the surface. Dry deposition and below-cloud scavenging are important for the profile of mineral dust only.
In this model, the microphysical processes of nucleation, condensation and coagulation dominate the vertical profile of the smallest particles by number (e.g. total CN > 3 nm), while the profiles of larger particles (e.g. CN > 100 nm) are controlled by the same processes as the component mass profiles, plus the size distribution of primary emissions.
We also show that the processes that affect the AOD-normalised radiative forcing in the model are predominantly those that affect the vertical mass distribution, in particular convective transport, in-cloud scavenging, aqueous oxidation, ageing and the vertical extent of biomass-burning emissions.

DOI： 10.5194/acp-16-2221-2016

Language：English   Publishing type：Research paper (scientific journal)  

Aerosol loading over the South Asian region has the potential to affect the monsoon rainfall, Himalayan glaciers and regional air-quality, with implications for the billions in this region. While field campaigns and network observations provide primary data, they tend to be location/season specific. Numerical models are useful to regionalize such location-specific data. Studies have shown that numerical models underestimate the aerosol scenario over the Indian region, mainly due to shortcomings related to meteorology and the emission inventories used. In this context, we have evaluated the performance of two such chemistry-transport models: WRF-Chem and SPRINTARS over an India-centric domain. The models differ in many aspects including physical domain, horizontal resolution, meteorological forcing and so on etc. Despite these differences, both the models simulated similar spatial patterns of Black Carbon (BC) mass concentration, (with a spatial correlation of 0.9 with each other), and a reasonable estimates of its concentration, though both of them under-estimated vis-a-vis the observations. While the emissions are lower (higher) in SPRINTARS (WRF-Chem), overestimation of wind parameters in WRF-Chem caused the concentration to be similar in both models. Additionally, we quantified the under-estimations of anthropogenic BC emissions in the inventories used these two models and three other widely used emission inventories. Our analysis indicates that all these emission inventories underestimate the emissions of BC over India by a factor that ranges from 1.5 to 2.9. We have also studied the model simulations of aerosol optical depth over the Indian region. The models differ significantly in simulations of AOD, with WRF-Chem having a better agreement with satellite observations of AOD as far as the spatial pattern is concerned. It is important to note that in addition to BC, dust can also contribute significantly to AOD. The models differ in simulations of the spatial pattern of mineral dust over the Indian region. We find that both meteorological forcing and emission formulation contribute to these differences. Since AOD is column integrated parameter, description of vertical profiles in both models, especially since elevated aerosol layers are often observed over Indian region, could be also a contributing factor. Additionally, differences in the prescription of the optical properties of BC between the models appear to affect the AOD simulations. We also compared simulation of sea-salt concentration in the two models and found that WRF-Chem underestimated its concentration vis-a-vis SPRINTARS. The differences in near-surface oceanic wind speeds appear to be the main source of this difference. In-spite of these differences, we note that there are similarities in their simulation of spatial patterns of various aerosol species (with each other and with observations) and hence models could be valuable tools for aerosol-related studies over the Indian region. Better estimation of emission inventories could improve aerosol-related simulations. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2015.10.065

Language：English   Publishing type：Research paper (scientific journal)  

The emissions of NOx and CO2 in East Asia (Northeast and Southeast Asia) contribute more than 30&#37; of the global total since 2008, and consequently the control of air pollutants and CO2 alleviating regional air pollution and global climate change is of great concern of not only in this region but also worldwide. In order to arrive at a rational view of the short-lived climate pollutants (SLCPs) co-control approach in East Asia, the effectiveness of the reduction of NOx/NMVOC and CH4 emissions for the reduction of tropospheric O-3 has been evaluated by individual and simultaneous 50&#37;-reduction of the emissions in Northeast Asia (NEA) using both a global chemical climate model (CHASER/SPRINTARS-MIROC), and a regional chemical transport model (WRF-CIVIAQ). The simultaneous reduction of NOx/NMVOC and CH4 emissions was found to reduce the regional concentration of surface O-3 in NEA, and globally averaged net radiative forcing most effectively.
Global mean RF and regional air quality change were also evaluated for the climate stabilization scenario ("450-ppm"), and climate stabilization with additional air pollution mitigation strengthened scenario ("450-ppm-cntr") developed in HASA with the aid of GAINS model. In the 450 ppm-cntr scenario, emissions of NOx NMVOC, BC and OC were further reduced respectively, for East Asia from the emissions in 450 ppm. The improvement of air quality as well as the mitigation of climate change would grant to the basis of the SLCP co-control approach in East Asia. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2015.10.003

Language：English   Publishing type：Research paper (scientific journal)  

The aerosol single-scattering albedo (SSA) over the global ocean is evaluated based on polarimetric measurements by the PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) satellite. For the first time, global ocean SSA and Absorption Aerosol Optical Depth (AAOD) from this instrument are shown and evaluated against other observations (the Aerosol Robotic Network, AERONET, and the Ozone Monitoring Instrument, OMI). The observational data sets compare reasonably well, with the majority of the colocated points within 0.05 of the AERONET measurements. PARASOL shows that SSA is characterized by high spatial and seasonal variability, also over the open ocean far from the inland emission regions. The near global coverage in the visible spectral range provided by the PARASOL retrievals represents a unique opportunity to evaluate aerosol optical properties simulated by global aerosol models, as performed in the Aerosol Comparisons between Observations and Models (AeroCom) framework. The SSA (AAOD) estimated by the AeroCom models is generally higher (smaller) than the SSA (AAOD) retrieved from PARASOL. On the other hand, the mean simulated aerosol optical depth is consistent or slightly underestimated compared with observations. An overestimate of the aerosol scattering, compared to absorption, by the models would suggest that these simulate an overly strong aerosol radiative cooling at top of atmosphere, over most of the ocean surfaces. This implies that aerosols have a potentially stronger direct and semidirect impact within the atmosphere than currently simulated.

DOI： 10.1002/2015JD023501

Language：English   Publishing type：Research paper (scientific journal)  

We examined the performance of autoconversion (mass transfer from cloud water to rainwater by the coalescence of cloud droplets) schemes in warm rain, which are commonly used in general circulation models. To exclude biases in the different treatment of the aerosol-cloud-precipitation-radiation interaction other than that of the autoconversion process, sensitivity experiments were conducted within a single model framework using an aerosol-climate model, MIROC-SPRINTARS. The liquid water path (LWP) and cloud optical thickness have a particularly high sensitivity to the autoconversion schemes, and their sensitivity is of the same magnitude as model biases. In addition, the ratio of accretion to autoconversion (Acc/Aut ratio), a key parameter in the examination of the balance of microphysical conversion processes, also has a high sensitivity globally depending on the scheme used. Although the Acc/Aut ratio monotonically increases with increasing LWP, significantly lower ratio is observed in Kessler-type schemes. Compared to satellite observations, a poor representation of cloud macrophysical structure and optically thicker low cloud are found in simulations with any autoconversion scheme. As a result of the cloud-radiation interaction, the difference in the global mean net cloud radiative forcing (NetCRF) among the schemes reaches 10 Wm(-2). The discrepancy between the observed and simulated NetCRF is especially large with a high LWP. The potential uncertainty in the parameterization of the autoconversion process is nonnegligible, and no formulation significantly improves the bias in the cloud radiative effect yet. This means that more fundamental errors are still left in other processes of the model.

DOI： 10.1002/2015JD023818

Language：English   Publishing type：Research paper (scientific journal)  

Sulfate aerosols simulated by an aerosol module coupled to the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) at a spatial resolution (220km) widely used by global climate models were evaluated by a comparison with in situ observations and the same aerosol module coupled to the Model for Interdisciplinary Research on Climate (MIROC) over East Asia for January, April, July, and October 2006. The results indicated that a horizontal gradient of sulfate from the source over China to the outflow over Korea-Japan was present in both the simulations and the observations. At the observation sites, the correlation coefficients of the sulfate concentrations between the simulations and the observations were high (NICAM: 0.49-0.89, MIROC: 0.61-0.77), whereas the simulated sulfate concentrations were lower than those obtained by the observation with the normalized mean bias of NICAM being -68 to -54&#37; (all), -77 to -63&#37; (source), and -67 to -30&#37; (outflow) and that of MIROC being -61 to -28&#37; (all), -77 to -63&#37; (source), and -60 to +2&#37; (outflow). Both NICAM and MIROC strongly underpredict surface SO2 over China source regions and Korea-Japan outflow regions, but the MIROC SO2 is much higher than NICAM SO2 over both regions. These differences between the models were mainly explained by differences in the sulfate formation within clouds and the dry deposition of SO2. These results indicated that the uncertainty of the meteorological and cloud fields as well as the vertical transport patterns between the different host climate models has a substantial impact on the simulated sulfate distribution.

DOI： 10.1002/2014JD021693

Language：Japanese   Publishing type：Research paper (scientific journal)  

Development of Seamless Chemical Assimilation System and Its Application for Atmospheric Environmental Materials(<Special Features>Introduction of Results from the MEXT "Research Program on Climate Change adaptation (RECCA)")

Language：English   Publishing type：Research paper (scientific journal)  

Atmospheric pollution over South Asia attracts special attention due to its effects on regional climate, water cycle and human health. These effects are potentially growing owing to rising trends of anthropogenic aerosol emissions. In this study, the spatio-temporal aerosol distributions over South Asia from seven global aerosol models are evaluated against aerosol retrievals from NASA satellite sensors and ground-based measurements for the period of 2000-2007. Overall, substantial underestimations of aerosol loading over South Asia are found systematically in most model simulations. Averaged over the entire South Asia, the annual mean aerosol optical depth (AOD) is underestimated by a range 15 to 44&#37; across models compared to MISR (Multi-angle Imaging SpectroRadiometer), which is the lowest bound among various satellite AOD retrievals (from MISR, SeaWiFS (Sea-Viewing Wide Field-of-View Sensor), MODIS (Moderate Resolution Imaging Spectroradiometer) Aqua and Terra). In particular during the postmonsoon and wintertime periods (i.e., October-January), when agricultural waste burning and anthropogenic emissions dominate, models fail to capture AOD and aerosol absorption optical depth (AAOD) over the Indo-Gangetic Plain (IGP) compared to ground-based Aerosol Robotic Network (AERONET) sunphotometer measurements. The underestimations of aerosol loading in models generally occur in the lower troposphere (below 2 km) based on the comparisons of aerosol extinction profiles calculated by the models with those from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data. Furthermore, surface concentrations of all aerosol components (sulfate, nitrate, organic aerosol (OA) and black carbon (BC)) from the models are found much lower than in situ measurements in winter. Several possible causes for these common problems of underestimating aerosols in models during the post-monsoon and wintertime periods are identified: the aerosol hygroscopic growth and formation of secondary inorganic aerosol are suppressed in the models because relative humidity (RH) is biased far too low in the boundary layer and thus foggy conditions are poorly represented in current models, the nitrate aerosol is either missing or inadequately accounted for, and emissions from agricultural waste burning and biofuel usage are too low in the emission inventories. These common problems and possible causes found in multiple models point out directions for future model improvements in this important region.

DOI： 10.5194/acp-15-5903-2015

Language：English   Publishing type：Research paper (scientific journal)  

Inverse modeling of Asian dust over the 8 year period 2005-2012 was performed with the Spectral Radiation-Transport Model for Aerosol Species/four-dimensional variational (SPRINTARS/4D-Var) data assimilation system and satellite-measured aerosol optical thickness over the ocean. We validated the inversion results with independent measurements provided by ground-based and space-based lidar and various in situ measurements. The inversion results were used to analyze interannual variations of Asian dust fluxes and relationships of these fluxes with climate indices. Dust emissions from central China and the Mongolian Plateau were 229-384 Tg yr(-1). The standard deviation of 55.3 Tg yr(-1) reflected large interannual variability. The frequency of dust storms and the beginning of the dust season in the source region also showed interannual variations. There was a meridional shift of the outflow path from the continent; the transport core was centered at 40-45 degrees N during southern transport years (2006-2007) and at 35-40 degrees N during northern transport years (2005 and 2008-2012). The fact that dust deposition showed a significant positive correlation with satellite-measured chlorophyll concentrations indicated that settled Asian dust enhanced phytoplankton blooms in the eastern North Pacific. Dust emissions were positively and negatively correlated with the Far Eastern Zonal and Dynamical Normalized Seasonality indices, respectively, the implication being that a strong meridional pressure gradient over the source region and a strong winter monsoon favor dust emission. The fact that the Southern Oscillation Index was positively correlated with dust emission, transport, and deposition suggests that Asian dust is affected by the El Nino-Southern Oscillation cycle and is enhanced during the La Nina phase.

DOI： 10.1002/2014JD022390

Language：English   Publishing type：Research paper (scientific journal)  

The present study focuses on identifying the main atmospheric circulation characteristics associated with aerosol episodes (AEs) over Kanpur, India during the period 2001-2010. In this respect, mean sea level pressure (MSLP) and geopotential height of 700 hPa (Z700) data obtained from the NCEP/ NCAR Reanalysis Project were used along with daily Terra-MODIS AOD(550) data. The analysis identifies 277 AEs [AOD(500) (AOD) over bar (500) + 1ST-DEV (standard deviation)] over Kanpur corresponding to 13.2 &#37; of the available AERONET dataset, which are seasonally distributed as 12.5, 9.1, 14.7 and 18.6 &#37; for winter (Dec-Feb), pre-monsoon (Mar-May), monsoon (Jun-Sep) and post-monsoon (Oct-Nov), respectively. The post-monsoon and winter AEs are mostly related to anthropogenic emissions, in contrast to pre-monsoon and monsoon episodes when a significant component of dust is found. The multivariate statistical methods Factor and Cluster Analysis are applied on the dataset of the AEs days' Z700 patterns over south Asia, to group them into discrete clusters. Six clusters are identified and for each of them the composite means for MSLP and Z700 as well as their anomalies from the mean 1981-2010 climatology are studied. Furthermore, the spatial distribution of Terra-MODIS AOD(550) over Indian sub-continent is examined to identify aerosol hot-spot areas for each cluster, while the SPRINTARS model simulations reveal incapability in reproducing the large anthropogenic AOD, suggesting need of further improvement in model emission inventories. This work is the first performed over India aiming to analyze and group the atmospheric circulation patterns associated with AEs over Indo-Gangetic Plains and to explore the influence of meteorology on the accumulation of aerosols.

DOI： 10.1007/s00382-014-2055-2

Language：English   Publishing type：Research paper (scientific journal)  

This study examines the characteristics of the microphysics and macrophysics of water clouds from East Asia to the North Pacific, using data from active CloudSat radar measurements and passive MODerate-resolution Imaging Spectroradiometer (MODIS) retrievals. Our goals are to clarify differences in microphysics and macrophysics between land and oceanic clouds, seasonal differences unique to the midlatitudes, characteristics of the drizzling process, and cloud vertical structure. In pristine oceanic areas, fractional occurrences of cloud optical thickness (COT) and cloud droplet effective radius (CDR) increase systematically with an increase in drizzle intensity, but these characteristics of the COT and CDR transition are less evident in polluted land areas. In addition, regional and seasonal differences are identified in terms of drizzle intensity as a function of the liquid water path (LWP) and cloud droplet number concentration (N-c). The correlations between drizzle intensity and LWP, and between drizzle intensity and N-c, are both more robust over oceanic areas than over land areas. We also demonstrate regional and seasonal characteristics of the cloud vertical structure. Our results suggest that aerosol-cloud interaction mainly occurs around the cloud base in polluted land areas during the winter season. In addition, a difference between polluted and pristine areas in the efficiency of cloud droplet growth is confirmed. These results suggest that water clouds over the midlatitudes exhibit a different drizzle system to those over the tropics.

DOI： 10.5194/acp-14-11935-2014

Language：English   Publishing type：Research paper (scientific journal)  

Atmospheric black carbon (BC) absorbs solar radiation, and exacerbates global warming through exerting positive radiative forcing (RF). However, the contribution of BC to ongoing changes in global climate is under debate. Anthropogenic BC emissions, and the resulting distribution of BC concentration, are highly uncertain. In particular, long-range transport and processes affecting BC atmospheric lifetime are poorly understood. Here we discuss whether recent assessments may have overestimated present-day BC radiative forcing in remote regions. We compare vertical profiles of BC concentration from four recent aircraft measurement campaigns to simulations by 13 aerosol models participating in the AeroCom Phase II intercomparison. An atmospheric lifetime of BC of less than 5 days is shown to be essential for reproducing observations in remote ocean regions, in line with other recent studies. Adjusting model results to measurements in remote regions, and at high altitudes, leads to a 25&#37; reduction in AeroCom Phase II median direct BC forcing, from fossil fuel and biofuel burning, over the industrial era. The sensitivity of modelled forcing to BC vertical profile and lifetime highlights an urgent need for further flight campaigns, close to sources and in remote regions, to provide improved quantification of BC effects for use in climate policy.

DOI： 10.5194/acp-14-12465-2014

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/1748-9326/9/10/104010

Language：English   Publishing type：Research paper (scientific journal)  

This paper evaluates the current status of global modeling of the organic aerosol (OA) in the troposphere and analyzes the differences between models as well as between models and observations. Thirty-one global chemistry transport models (CTMs) and general circulation models (GCMs) have participated in this intercomparison, in the framework of AeroCom phase II. The simulation of OA varies greatly between models in terms of the magnitude of primary emissions, secondary OA (SOA) formation, the number of OA species used (2 to 62), the complexity of OA parameterizations (gas-particle partitioning, chemical aging, multiphase chemistry, aerosol microphysics), and the OA physical, chemical and optical properties. The diversity of the global OA simulation results has increased since earlier AeroCom experiments, mainly due to the increasing complexity of the SOA parameterization in models, and the implementation of new, highly uncertain, OA sources. Diversity of over one order of magnitude exists in the modeled vertical distribution of OA concentrations that deserves a dedicated future study. Furthermore, although the OA/OC ratio depends on OA sources and atmospheric processing, and is important for model evaluation against OA and OC observations, it is resolved only by a few global models.
The median global primary OA (POA) source strength is 56 Tg a(-1) (range 34-144 Tg a(-1)) and the median SOA source strength (natural and anthropogenic) is 19 Tg a(-1) (range 13-121 Tg a(-1)). Among the models that take into account the semi-volatile SOA nature, the median source is calculated to be 51 Tg a(-1) (range 16-121 Tg a(-1)), much larger than the median value of the models that calculate SOA in a more simplistic way (19 Tg a(-1); range 13-20 Tg a(-1), with one model at 37 Tg a(-1)). The median atmospheric burden of OA is 1.4 Tg (24 models in the range of 0.6-2.0 Tg and 4 between 2.0 and 3.8 Tg), with a median OA lifetime of 5.4 days (range 3.8-9.6 days). In models that reported both OA and sulfate burdens, the median value of the OA/sulfate burden ratio is calculated to be 0.77; 13 models calculate a ratio lower than 1, and 9 models higher than 1. For 26 models that reported OA deposition fluxes, the median wet removal is 70 Tg a(-1) (range 28-209 Tg a(-1)), which is on average 85&#37; of the total OA deposition.
Fine aerosol organic carbon (OC) and OA observations from continuous monitoring networks and individual field campaigns have been used for model evaluation. At urban locations, the model-observation comparison indicates missing knowledge on anthropogenic OA sources, both strength and seasonality. The combined model-measurements analysis suggests the existence of increased OA levels during summer due to biogenic SOA formation over large areas of the USA that can be of the same order of magnitude as the POA, even at urban locations, and contribute to the measured urban seasonal pattern.
Global models are able to simulate the high secondary character of OA observed in the atmosphere as a result of SOA formation and POA aging, although the amount of OA present in the atmosphere remains largely underestimated, with a mean normalized bias (MNB) equal to -0.62 (-0.51) based on the comparison against OC (OA) urban data of all models at the surface, -0.15 (+0.51) when compared with remote measurements, and -0.30 for marine locations with OC data. The mean temporal correlations across all stations are low when compared with OC (OA) measurements: 0.47 (0.52) for urban stations, 0.39 (0.37) for remote stations, and 0.25 for marine stations with OC data. The combination of high (negative) MNB and higher correlation at urban stations when compared with the low MNB and lower correlation at remote sites suggests that knowledge about the processes that govern aerosol processing, transport and removal, on top of their sources, is important at the remote stations. There is no clear change in model skill with increasing model complexity with regard to OC or OA mass concentration. However, the complexity is needed in models in order to distinguish between anthropogenic and natural OA as needed for climate mitigation, and to calculate the impact of OA on climate accurately.

DOI： 10.5194/acp-14-10845-2014

Language：English   Publishing type：Research paper (scientific journal)  

Fine particulate matter with diameter of 2.5 mu m or less (PM2.5) is associated with premature mortality and can travel long distances, impacting air quality and health on intercontinental scales. We estimate the mortality impacts of 20 &#37; anthropogenic primary PM2.5 and PM2.5 precursor emission reductions in each of four major industrial regions (North America, Europe, East Asia, and South Asia) using an ensemble of global chemical transport model simulations coordinated by the Task Force on Hemispheric Transport of Air Pollution and epidemiologically-derived concentration-response functions. We estimate that while 93-97 &#37; of avoided deaths from reducing emissions in all four regions occur within the source region, 3-7 &#37; (11,500; 95 &#37; confidence interval, 8,800-14,200) occur outside the source region from concentrations transported between continents. Approximately 17 and 13 &#37; of global deaths avoided by reducing North America and Europe emissions occur extraregionally, owing to large downwind populations, compared with 4 and 2 &#37; for South and East Asia. The coarse resolution global models used here may underestimate intraregional health benefits occurring on local scales, affecting these relative contributions of extraregional versus intraregional health benefits. Compared with a previous study of 20 &#37; ozone precursor emission reductions, we find that despite greater transport efficiency for ozone, absolute mortality impacts of intercontinental PM2.5 transport are comparable or greater for neighboring source-receptor pairs, due to the stronger effect of PM2.5 on mortality. However, uncertainties in modeling and concentration-response relationships are large for both estimates.

DOI： 10.1007/s11869-014-0248-9

Language：Japanese   Publishing type：Research paper (scientific journal)  

Modeling Studies on Aerosol-Climate Interaction

Language：English   Publishing type：Research paper (scientific journal)  

A series of 60-year numerical experiments starting from 1851 was conducted using a global climate model coupled with an aerosol-cloud-radiation model to investigate the response of the Asian summer monsoon to variations in the secondary organic aerosol (SOA) flux induced by two different estimations of biogenic volatile organic compound (BVOC) emissions. One estimation was obtained from a pre-existing archive and the other was generated by a next-generation model (the Model of Emissions of Gases and Aerosols from Nature, MEGAN). The use of MEGAN resulted in an overall increase of the SOA production through a higher rate of gasto-particle conversion of BVOCs. Consequently, the atmospheric loading of organic carbon (OC) increased due to the contribution of SOA to OC aerosol. The increase of atmospheric OC aerosols was prominent in particular in the Indian subcontinent and Indochina Peninsula (IP) during the pre- and early-monsoon periods because the terrestrial biosphere is the major source of BVOC emissions and the atmospheric aerosol concentration diminishes rapidly with the arrival of monsoon rainfall. As the number of atmospheric OC particles increased, the number concentrations of cloud droplets increased, but their size decreased. These changes represent a combination of aerosol-cloud interactions that were favorable to rainfall suppression. However, the modeled precipitation was slightly enhanced in May over the oceans that surround the Indian subcontinent and IP. Further analysis revealed that a compensating updraft in the surrounding oceans was induced by the thermally-driven downdraft in the IP, which was a result of surface cooling associated with direct OC aerosol radiative forcing, and was able to surpass the aerosolcloud interactions. The co-existence of oceanic ascending motion with the maximum convective available potential energy was also found to be crucial for rainfall formation. Although the model produced statistically significant rainfall changes with locally organized patterns, the suggested pathways should be considered guardedly because in the simulation results, 1) the BVOC-induced aerosol direct effect was marginal; 2) cloud-aerosol interactions were modeldependent; and 3) Asian summer monsoons were biased to a nonnegligible extent.

DOI： 10.1007/s13143-014-0033-6

Language：English   Publishing type：Research paper (scientific journal)  

In order to examine the spatial variability of the aerosol characteristics across the Brahmaputra valley, a land campaign was conducted during late winter (February 3-March 2) 2011. Measurements of particulate matter (PM, PM10, PM2.5) and black carbon (BC) concentrations were made onboard an interior redesigned vehicle. The length of the campaign trail stretched about 700 km, covering the longitude belt of 89.97 degrees-95.55 degrees E and latitude belt of 26.1 degrees-27.6 degrees N, comprising 13 measurement locations. The valley is divided into three sectors longitudinally: western sector (R1: 89.97 degrees-91.75 degrees E), middle sector (R2: 92.5 degrees-94.01 degrees E) and eastern sector (R3: 94.63 degrees-95.55 degrees E). Spatial heterogeneity in aerosol distribution has been observed with higher PM10 and PM2.5 concentrations at the western and middle sectors compared to the eastern sector. The locations in the western sector are found to be rich in BC compared to the other two sectors and there is a gradual decrease in BC concentrations from west to east of the Brahmaputra valley. Two hotspots within the western and middle sectors with high PM and BC concentrations have been identified. The associated physico-optical parameters of PM reveal abundance of PM2.5 aerosols along the entire valley. High population density in the western and middle sectors, together with the contribution of remote aerosols, leads to higher anthropogenic aerosols over those regions. Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) slightly underestimates the measured PM10 and PM2.5 at the eastern sector while the model overestimates the measurements at a number of locations in the western sector. In general, BC is underestimated by the model. The variation of BC within the campaign trail has not been adequately captured by the model leading to higher variance in the western locations as compared to the middle and eastern locations.

DOI： 10.1007/s12040-014-0431-2

Language：English   Publishing type：Research paper (scientific journal)  

This study evaluates model-simulated dust aerosols over North Africa and the North Atlantic from five global models that participated in the Aerosol Comparison between Observations and Models phase II model experiments. The model results are compared with satellite aerosol optical depth (AOD) data from Moderate Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging Spectroradiometer (MISR), and Sea-viewing Wide Field-of-view Sensor, dust optical depth (DOD) derived from MODIS and MISR, AOD and coarse-mode AOD (as a proxy of DOD) from ground-based Aerosol Robotic Network Sun photometer measurements, and dust vertical distributions/centroid height from Cloud Aerosol Lidar with Orthogonal Polarization and Atmospheric Infrared Sounder satellite AOD retrievals. We examine the following quantities of AOD and DOD: (1) the magnitudes over land and over ocean in our study domain, (2) the longitudinal gradient from the dust source region over North Africa to the western North Atlantic, (3) seasonal variations at different locations, and (4) the dust vertical profile shape and the AOD centroid height (altitude above or below which half of the AOD is located). The different satellite data show consistent features in most of these aspects
however, the models display large diversity in all of them, with significant differences among the models and between models and observations. By examining dust emission, removal, and mass extinction efficiency in the five models, we also find remarkable differences among the models that all contribute to the discrepancies of model-simulated dust amount and distribution. This study highlights the challenges in simulating the dust physical and optical processes, even in the best known dust environment, and stresses the need for observable quantities to constrain the model processes.

DOI： 10.1002/2013JD021099

Language：English   Publishing type：Research paper (scientific journal)  

Though many global aerosols models prognose surface deposition, only a few models have been used to directly simulate the radiative effect from black carbon (BC) deposition to snow and sea ice. Here, we apply aerosol deposition fields from 25 models contributing to two phases of the Aerosol Comparisons between Observations and Models (AeroCom) project to simulate and evaluate within-snow BC concentrations and radiative effect in the Arctic. We accomplish this by driving the offline land and sea ice components of the Community Earth System Model with different deposition fields and meteorological conditions from 2004 to 2009, during which an extensive field campaign of BC measurements in Arctic snow occurred. We find that models generally underestimate BC concentrations in snow in northern Russia and Norway, while overestimating BC amounts elsewhere in the Arctic. Although simulated BC distributions in snow are poorly correlated with measurements, mean values are reasonable. The multi-model mean (range) bias in BC concentrations, sampled over the same grid cells, snow depths, and months of measurements, are -4.4 (-13.2 to + 10.7) ng g(-1) for an earlier phase of AeroCom models (phase I), and + 4.1 (-13.0 to + 21.4) ng g(-1) for a more recent phase of AeroCom models (phase II), compared to the observational mean of 19.2 ng g(-1). Factors determining model BC concentrations in Arctic snow include Arctic BC emissions, transport of extra-Arctic aerosols, precipitation, deposition efficiency of aerosols within the Arctic, and meltwater removal of particles in snow. Sensitivity studies show that the model-measurement evaluation is only weakly affected by meltwater scavenging efficiency because most measurements were conducted in non-melting snow. The Arctic (60-90 degrees N) atmospheric residence time for BC in phase II models ranges from 3.7 to 23.2 days, implying large inter-model variation in local BC deposition efficiency. Combined with the fact that most Arctic BC deposition originates from extra-Arctic emissions, these results suggest that aerosol removal processes are a leading source of variation in model performance. The multi-model mean (full range) of Arctic radiative effect from BC in snow is 0.15 (0.07-0.25) W m(-2) and 0.18 (0.06-0.28) W m(-2) in phase I and phase II models, respectively. After correcting for model biases relative to observed BC concentrations in different regions of the Arctic, we obtain a multi-model mean Arctic radiative effect of 0.17W m(-2) for the combined AeroCom ensembles. Finally, there is a high correlation between modeled BC concentrations sampled over the observational sites and the Arctic as a whole, indicating that the field campaign provided a reasonable sample of the Arctic.

DOI： 10.5194/acp-14-2399-2014

Language：English   Publishing type：Research paper (scientific journal)  

Mixed-phase clouds (clouds that consist of both cloud droplets and ice crystals) are frequently present in the Earth's atmosphere and influence the Earth's energy budget through their radiative properties, which are highly dependent on the cloud water phase. In this study, the phase partitioning of cloud water is compared among six global climate models (GCMs) and with Cloud and Aerosol Lidar with Orthogonal Polarization retrievals. It is found that the GCMs predict vastly different distributions of cloud phase for a given temperature, and none of them are capable of reproducing the spatial distribution or magnitude of the observed phase partitioning. While some GCMs produced liquid water paths comparable to satellite observations, they all failed to preserve sufficient liquid water at mixed-phase cloud temperatures. Our results suggest that validating GCMs using only the vertically integrated water contents could lead to amplified differences in cloud radiative feedback. The sensitivity of the simulated cloud phase in GCMs to the choice of heterogeneous ice nucleation parameterization is also investigated. The response to a change in ice nucleation is quite different for each GCM, and the implementation of the same ice nucleation parameterization in all models does not reduce the spread in simulated phase among GCMs. The results suggest that processes subsequent to ice nucleation are at least as important in determining phase and should be the focus of future studies aimed at understanding and reducing differences among the models.

DOI： 10.1002/2013JD021119

Language：English   Publishing type：Research paper (scientific journal)  

On seasonal and interannual time scales, weather is highly influential in aerosol variability. In this study, we investigate the relationship between fine-mode AOD (fAOD) and precipitation on these scales, in order to unravel the effect of wet weather on aerosol amount. We find with integrated satellite and ground observations that biomass burning related fAOD has a relatively greater seasonal variation than fossil fuel combustion related fAOD. It is also found that wet weather reduces biomass burning fAOD and increases fossil fuel combustion fAOD. Aerosol simulation models forced by reanalyses consistently simulate the biomass burning fAOD reduced during wet weather but only in the tropics and furthermore do not consistently increase fossil fuel combustion fAOD during wet conditions. The identified relationship between fAOD and precipitation in observations allows for seasonal predictability of fAOD, since average precipitation can be predicted a few to several months in advance due to the well-established predictability of El Nino-Southern Oscillation (ENSO). We reveal ENSO-covariant fAOD using a rotated component principal analysis of combined interannual variation of sea surface temperature, precipitation and fAOD. During the warm phase of ENSO, we find that fAOD increases over Indonesia and the eastern coastal area of China, and decreases over South Asia, the Amazon and the continental parts of China.

DOI： 10.3402/tellusb.v66.23037

Language：English   Publishing type：Research paper (scientific journal)  

The quantification and understanding of direct aerosol forcing is essential in the study of climate. One of the main issues that makes its quantification difficult is the lack of a complete understanding of the role of the vertical distribution of aerosols and clouds. This work aims at reducing the uncertainty of aerosol top-of-the-atmosphere (TOA) forcing due to the vertical superposition of several short-lived atmospheric components, in particular different aerosol species and clouds. We propose a method to quantify the contribution of different parts of the atmospheric column to the TOA forcing as well as to evaluate the contribution to model differences that is exclusively due to different spatial distributions of aerosols and clouds. We investigate the contribution of aerosol above, below and in clouds by using added diagnostics in the aerosol-climate model LMDz. We also compute the difference between the TOA forcing of the ensemble of the aerosols and the sum of the forcings from individual species in clear sky. This difference is found to be moderate for the global average (14 &#37;) but can reach high values regionally (up to 100 &#37;). Nonlinear effects are even more important when superposing aerosols and clouds. Four forcing computations are performed: one where the full aerosol 3-D distribution is used, and then three where aerosols are confined to regions above, inside and below clouds, respectively. We find that the TOA forcing of aerosols depends crucially on the presence of clouds and on their position relative to that of the aerosol, in particular for black carbon (BC). We observe a strong enhancement of the TOA forcing of BC above clouds, attenuation for BC below clouds, and a moderate enhancement when BC is found within clouds. BC above clouds accounts for only about 30 &#37; of the total BC optical depth but for 55 &#37; of the forcing, while forcing efficiency increases by a factor of 7.5 when passing from below to above clouds.
The different behaviour of forcing nonlinearities for these three components of the atmospheric column encouraged us to develop the method for application to inter-model variability studies by reading 3-D aerosol and cloud fields from different general circulation models (GCMs) into the same model. We apply the method to the comparison of forcing due to the aerosols and clouds distributions of the general circulation models LMDz and SPRINTARS. The different amount of BC above but also within clouds is revealed to play a major role on the differences of cloudy-sky forcings between the two models, which can exceed 100&#37; regionally.

DOI： 10.5194/acp-14-877-2014

Language：Japanese   Publishing type：Research paper (scientific journal)  

An analysis of high sulfate ion events observed in Fukuoka and Osaka city in summer, 2012
We observed high sulfate ion concentrations in Fukuoka and Osaka city using an aerosol mass spectrometer and an ion chromatograph method in the end of July, 2012. The mass concentration of sulfate ion reached ca. 35 μg m^-3 on 25 July in Fukuoka. The mass concentration of PM_2.5 exceeded 50 μg m^-3 and that of sulfate ion was between 10and 20 μg m^-3 for several hours on 29 July in Osaka. The simulation using Spectral Radiation- Transport Model for Aerosol Species (SPRINTARS) showed that the air mass with a high sulfate ion concentration first covered the Korean peninsula in July 2012 and then spread over the northern part of Kyushu and the Honshu regions of Japan. This indicates that the observed high sulfate ion events were possibly due to the trans-boundary air pollution. Since air pollution with a high sulfate ion concentration potentially causes adverse health effect, the monitoring of trans-boundary air pollution is necessary even in summer.

DOI： 10.11203/jar.28.281

Language：English   Publishing type：Research paper (scientific journal)  

We present an aerosol data assimilation system based on a global aerosol climate model (SPRINTARS - Spectral Radiation-Transport Model for Aerosol Species) and a four-dimensional variational data assimilation method (4D-Var). Its main purposes are to optimize emission estimates, improve composites, and obtain the best estimate of the radiative effects of aerosols in conjunction with observations. To reduce the huge computational cost caused by the iterative integrations in the models, we developed an offline model and a corresponding adjoint model, which are driven by pre-calculated meteorological, land, and soil data. The offline and adjoint model shortened the computational time of the inner loop by more than 30&#37;.
By comparing the results with a 1 yr simulation from the original online model, the consistency of the offline model was verified, with correlation coefficient R > 0.97 and absolute value of normalized mean bias NMB < 7&#37; for the natural aerosol emissions and aerosol optical thickness (AOT) of individual aerosol species. Deviations between the offline and original online models are mainly associated with the time interpolation of the input meteorological variables in the offline model; the smaller variability and difference in the wind velocity near the surface and relative humidity cause negative and positive biases in the wind-blown aerosol emissions and AOTs of hygroscopic aerosols, respectively.
The feasibility and capability of the developed system for aerosol inverse modelling was demonstrated in several inversion experiments based on the observing system simulation experiment framework. In the experiments, we used the simulated observation data sets of fine- and coarse-mode AOTs from sun-synchronous polar orbits to investigate the impact of the observational frequency (number of satellites) and coverage (land and ocean), and assigned aerosol emissions to control parameters. Observations over land have a notably positive impact on the performance of inverse modelling as compared with observations over ocean, implying that reliable observational information over land is important for inverse modelling of land-born aerosols. The experimental results also indicate that information that provides differentiations between aerosol species is crucial to inverse modelling over regions where various aerosol species coexist (e.g. industrialized regions and areas downwind of them).

DOI： 10.5194/gmd-6-2005-2013

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3769/radioisotopes.62.847

Language：English   Publishing type：Research paper (scientific journal)  

One of the major factors attributed to the accelerated melting of Himalayan glaciers is the snow darkening effect of atmospheric black carbon (BC). The BC is the result of incomplete fossil fuel combustion from sources such as open biomass burning and wood burning cooking stoves. One of the key challenges in determining the darkening effect is the estimation uncertainty of BC deposition (BCD) rate on surface snow cover. Here we analyze the variation of BC dry deposition in seven different estimates based on different dry deposition methods which include different atmospheric forcings (observations and global model outputs) and different spatial resolutions. The seven simulations are used to estimate the uncertainty range of BC dry deposition over the southern Himalayas during pre-monsoon period (March-May) in 2006. Our results show BC dry deposition rates in a wide range of 270-4700 mu g m(-2) during the period. Two global models generate higher BC dry deposition rates due to modeled stronger surface wind and simplification of complicated sub-grid surface conditions in this region. Using ice surface roughness and observation-based meteorological data, we estimate a better range of BC dry deposition rate of 900-1300 mu g m(-2). Under dry and highly polluted conditions, aged snow and sulfate-coated BC are expected to possibly reduce visible albedo by 4.2-5.1&#37;. Our results suggest that for estimating aerosol-induced snow darkening effects of Himalaya snowpacks using global and regional models, realistic physical representation of ice or snow surface roughness and surface wind speed are critical in reducing uncertainties on the estimate of BC deposition over snow surface. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2012.03.031

Language：English   Publishing type：Research paper (scientific journal)  

Increased concentrations of ozone and fine particulate matter (PM2.5) since preindustrial times reflect increased emissions, but also contributions of past climate change. Here we use modeled concentrations from an ensemble of chemistry-climate models to estimate the global burden of anthropogenic outdoor air pollution on present-day premature human mortality, and the component of that burden attributable to past climate change. Using simulated concentrations for 2000 and 1850 and concentration-response functions (CRFs), we estimate that, at present, 470 000 (95&#37; confidence interval, 140 000 to 900 000) premature respiratory deaths are associated globally and annually with anthropogenic ozone, and 2.1 (1.3 to 3.0) million deaths with anthropogenic PM2.5-related cardiopulmonary diseases (93&#37;) and lung cancer (7&#37;). These estimates are smaller than ones from previous studies because we use modeled 1850 air pollution rather than a counterfactual low concentration, and because of different emissions. Uncertainty in CRFs contributes more to overall uncertainty than the spread of model results. Mortality attributed to the effects of past climate change on air quality is considerably smaller than the global burden: 1500 (-20 000 to 27 000) deaths yr(-1) due to ozone and 2200 (-350 000 to 140 000) due to PM2.5. The small multi-model means are coincidental, as there are larger ranges of results for individual models, reflected in the large uncertainties, with some models suggesting that past climate change has reduced air pollution mortality.

DOI： 10.1088/1748-9326/8/3/034005

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.5194/acp-13-6553-2013

Language：English   Publishing type：Research paper (scientific journal)  

Changes in global temperature are generally more marked in high than in low latitudes, an effect referred to as polar amplification(1-3). Model simulations of future climate suggest a marked response of high-latitude climate due to elevated greenhouse-gas concentrations and associated albedo feedbacks(4). However, most climate models struggle to reproduce the amplitude of polar temperature change observed in palaeoclimatic archives(3) and may carry this bias into future predictions. With the example of mineral dust we show that some atmospheric aerosols experience an amplified high-latitude response to global changes as well, a phenomenon generally not captured by the models. Using a synthesis of observational and model data we reconstruct atmospheric dust concentrations for Holocene and Last Glacial Maximum (LGM) conditions. Radiative forcing calculations based on our new dust concentration reconstructions suggest that the impact of aerosols in polar areas is underestimated in model simulations for dustier-than-modern conditions. In the future, some simulations predict an increase in aridity in dust source areas(5). Other aerosols such as black carbon and sulphates are likely to increase as well(6,7). We therefore suggest that the inclusion of the amplified high-latitude response of aerosols in atmospheric models would improve the assessment of LGM and future polar amplification.

DOI： 10.1038/NCLIMATE1785

Language：English   Publishing type：Research paper (scientific journal)  

The long term climatology of PM10 and PM2.5 concentrations for the five year period from June 2007-March 2012 is studied using measurements made with a Quartz Crystal Microbalance Impactor over Dibrugarh, North-East India. The PM10 and PM2.5 exhibit similar seasonal variability with maximum concentration in winter and minimum in monsoon seasons. The PM10 concentration is mainly attributed to PM2.5 with minimal contribution from PM10-2.5. The long term monthly mean PM10 and PM2.5 concentrations shows maximum value in late winter and early pre-monsoon. This temporal variability is positively correlated with the MODIS retrieved fire counts associated mostly with the biomass burning activities and negatively correlated with rainfall. PM10 and PM2.5 gradually increased from 2007 to 2010 and decreased thereafter. An overall slow decreasing trend in PM10 and PM2.5 concentrations together with black carbon (BC) concentrations has been observed. The examination of microphysical and optical properties also reveals the dominance of PM2.5 aerosols. Higher percentage contributions of BC to both PM10 and PM2.5 are observed in post-monsoon season followed by winter. The inter-comparison of measured PM and BC concentrations with SPRINTARS simulation reveals that model underestimates the measurements except in pre-monsoon. The discrepancy might have arisen due to the topography of the location and inadequate emission inventory for the climate zone. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2012.12.032

Language：English   Publishing type：Research paper (scientific journal)  

As part of the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), we evaluate the historical black carbon (BC) aerosols simulated by 8 ACCMIP models against observations including 12 ice core records, long-term surface mass concentrations, and recent Arctic BC snowpack measurements. We also estimate BC albedo forcing by performing additional simulations using offline models with prescribed meteorology from 1996-2000. We evaluate the vertical profile of BC snow concentrations from these offline simulations using the recent BC snowpack measurements. Despite using the same BC emissions, the global BC burden differs by approximately a factor of 3 among models due to differences in aerosol removal parameterizations and simulated meteorology: 34 Gg to 103 Gg in 1850 and 82 Gg to 315 Gg in 2000. However, the global BC burden from preindustrial to present-day increases by 2.5-3 times with little variation among models, roughly matching the 2.5-fold increase in total BC emissions during the same period.We find a large divergence among models at both Northern Hemisphere (NH) and Southern Hemisphere (SH) high latitude regions for BC burden and at SH high latitude regions for deposition fluxes. The ACCMIP simulations match the observed BC surface mass concentrations well in Europe and North America except at Ispra. However, the models fail to predict the Arctic BC seasonality due to severe underestimations during winter and spring. The simulated vertically resolved BC snow concentrations are, on average, within a factor of 2-3 of the BC snowpack measurements except for Greenland and the Arctic Ocean. For the ice core evaluation, models tend to adequately capture both the observed temporal trends and the magnitudes at Greenland sites. However, models fail to predict the decreasing trend of BC depositions/ice core concentrations from the 1950s to the 1970s in most Tibetan Plateau ice cores. The distinct temporal trend at the Tibetan Plateau ice cores indicates a strong influence from Western Europe, but the modeled BC increases in that period are consistent with the emission changes in Eastern Europe, the Middle East, South and East Asia. At the Alps site, the simulated BC suggests a strong influence from Europe, which agrees with the Alps ice core observations. At Zuoqiupu on the Tibetan Plateau, models successfully simulate the higher BC concentrations observed during the non-monsoon season compared to the monsoon season but overpredict BC in both seasons. Despite a large divergence in BC deposition at two Antarctic ice core sites, some models with a BC lifetime of less than 7 days are able to capture the observed concentrations. In 2000 relative to 1850, globally and annually averaged BC surface albedo forcing from the offline simulations ranges from 0.014 to 0.019Wm-2 among the ACCMIP models. Comparing offline and online BC albedo forcings computed by some of the same models, we find that the global annual mean can vary by up to a factor of two because of different aerosol models or different BC-snow parameterizations and snow cover. The spatial distributions of the offline BC albedo forcing in 2000 show especially high BC forcing (i.e., over 0.1Wm-2) over Manchuria, Karakoram, and most of the Former USSR. Models predict the highest global annual mean BC forcing in 1980 rather than 2000, mostly driven by the high fossil fuel and biofuel emissions in the Former USSR in 1980.

DOI： 10.5194/acp-13-2607-2013

Language：English   Publishing type：Research paper (scientific journal)  

Simulated multi-model "diversity" in aerosol direct radiative forcing estimates is often perceived as a measure of aerosol uncertainty. However, current models used for aerosol radiative forcing calculations vary considerably in model components relevant for forcing calculations and the associated "host-model uncertainties" are generally convoluted with the actual aerosol uncertainty. In this AeroCom Prescribed intercomparison study we systematically isolate and quantify host model uncertainties on aerosol forcing experiments through prescription of identical aerosol radiative properties in twelve participating models.
Even with prescribed aerosol radiative properties, simulated clear-sky and all-sky aerosol radiative forcings show significant diversity. For a purely scattering case with globally constant optical depth of 0.2, the global-mean all-sky top-of-atmosphere radiative forcing is -4.47 Wm(-2) and the inter-model standard deviation is 0.55 Wm(-2), corresponding to a relative standard deviation of 12 &#37;. For a case with partially absorbing aerosol with an aerosol optical depth of 0.2 and single scattering albedo of 0.8, the forcing changes to 1.04 Wm(-2), and the standard deviation increases to 1.01 W-2, corresponding to a significant relative standard deviation of 97 &#37;. However, the top-of-atmosphere forcing variability owing to absorption (subtracting the scattering case from the case with scattering and absorption) is low, with absolute (relative) standard deviations of 0.45 Wm(-2) (8 &#37;) clear-sky and 0.62 Wm(-2) (11 &#37;) all-sky.
Scaling the forcing standard deviation for a purely scattering case to match the sulfate radiative forcing in the AeroCom Direct Effect experiment demonstrates that host model uncertainties could explain about 36&#37; of the overall sulfate forcing diversity of 0.11 Wm(-2) in the AeroCom Direct Radiative Effect experiment.
Host model errors in aerosol radiative forcing are largest in regions of uncertain host model components, such as stratocumulus cloud decks or areas with poorly constrained surface albedos, such as sea ice. Our results demonstrate that host model uncertainties are an important component of aerosol forcing uncertainty that require further attention.

DOI： 10.5194/acp-13-3245-2013

Language：English   Publishing type：Research paper (scientific journal)  

The Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) examined the short-lived drivers of climate change in current climate models. Here we evaluate the 10 ACCMIP models that included aerosols, 8 of which also participated in the Coupled Model Intercomparison Project phase 5 (CMIP5). The models reproduce present-day total aerosol optical depth (AOD) relatively well, though many are biased low. Contributions from individual aerosol components are quite different, however, and most models underestimate east Asian AOD. The models capture most 1980-2000 AOD trends well, but underpredict increases over the Yellow/Eastern Sea. They strongly underestimate absorbing AOD in many regions. We examine both the direct radiative forcing (RF) and the forcing including rapid adjustments (effective radiative forcing
ERF, including direct and indirect effects). The models' all-sky 1850 to 2000 global mean annual average total aerosol RF is (mean
range) -0.26Wm-2
-0.06 to -0.49Wm-2. Screening based on model skill in capturing observed AOD yields a best estimate of -0.42Wm-2
-0.33 to -0.50Wm-2, including adjustment for missing aerosol components in some models. Many ACCMIP and CMIP5 models appear to produce substantially smaller aerosol RF than this best estimate. Climate feedbacks contribute substantially (35 to -58 &#37;) to modeled historical aerosol RF. The 1850 to 2000 aerosol ERF is -1.17Wm -2
-0.71 to -1.44Wm-2. Thus adjustments, including clouds, typically cause greater forcing than direct RF. Despite this, the multi-model spread relative to the mean is typically the same for ERF as it is for RF, or even smaller, over areas with substantial forcing. The largest 1850 to 2000 negative aerosol RF and ERF values are over and near Europe, south and east Asia and North America. ERF, however, is positive over the Sahara, the Karakoram, high Southern latitudes and especially the Arctic. Global aerosol RF peaks in most models around 1980, declining thereafter with only weak sensitivity to the Representative Concentration Pathway (RCP). One model, however, projects approximately stable RF levels, while two show increasingly negative RF due to nitrate (not included in most models). Aerosol ERF, in contrast, becomes more negative during 1980 to 2000. During this period, increased Asian emissions appear to have a larger impact on aerosol ERF than European and North American decreases due to their being upwind of the large, relatively pristine Pacific Ocean. There is no clear relationship between historical aerosol ERF and climate sensitivity in the CMIP5 subset of ACCMIP models. In the ACCMIP/CMIP5 models, historical aerosol ERF of about -0.8 to -1.5Wm-2 is most consistent with observed historical warming. Aerosol ERF masks a large portion of greenhouse forcing during the late 20th and early 21st century at the global scale. Regionally, aerosol ERF is so large that net forcing is negative over most industrialized and biomass burning regions through 1980, but remains strongly negative only over east and southeast Asia by 2000. Net forcing is strongly positive by 1980 over most deserts, the Arctic, Australia, and most tropical oceans. Both the magnitude of and area covered by positive forcing expand steadily thereafter. © Author(s) 2013.

DOI： 10.5194/acp-13-2939-2013

Language：English   Publishing type：Research paper (scientific journal)  

The impact of black carbon (BC) aerosols on the global radiation balance is not well constrained. Here twelve global aerosol models are used to show that at least 20&#37; of the present uncertainty in modeled BC direct radiative forcing (RF) is due to diversity in the simulated vertical profile of BC mass. Results are from phases 1 and 2 of the global aerosol model intercomparison project (AeroCom). Additionally, a significant fraction of the variability is shown to come from high altitudes, as, globally, more than 40&#37; of the total BC RF is exerted above 5 km. BC emission regions and areas with transported BC are found to have differing characteristics. These insights into the importance of the vertical profile of BC lead us to suggest that observational studies are needed to better characterize the global distribution of BC, including in the upper troposphere.

DOI： 10.5194/acp-13-2423-2013

Language：English   Publishing type：Research paper (scientific journal)  

We report on the AeroCom Phase II direct aerosol effect (DAE) experiment where 16 detailed global aerosol models have been used to simulate the changes in the aerosol distribution over the industrial era. All 16 models have estimated the radiative forcing (RF) of the anthropogenic DAE, and have taken into account anthropogenic sulphate, black carbon (BC) and organic aerosols (OA) from fossil fuel, biofuel, and biomass burning emissions. In addition several models have simulated the DAE of anthropogenic nitrate and anthropogenic influenced secondary organic aerosols (SOA). The model simulated all-sky RF of the DAE from total anthropogenic aerosols has a range from -0.58 to -0.02 Wm(-2), with a mean of -0.27 Wm(-2) for the 16 models. Several models did not include nitrate or SOA and modifying the estimate by accounting for this with information from the other AeroCom models reduces the range and slightly strengthens the mean. Modifying the model estimates for missing aerosol components and for the time period 1750 to 2010 results in a mean RF for the DAE of -0.35 Wm(-2). Compared to AeroCom Phase I (Schulz et al., 2006) we find very similar spreads in both total DAE and aerosol component RF. However, the RF of the total DAE is stronger negative and RF from BC from fossil fuel and biofuel emissions are stronger positive in the present study than in the previous AeroCom study. We find a tendency for models having a strong (positive) BC RF to also have strong (negative) sulphate or OA RF. This relationship leads to smaller uncertainty in the total RF of the DAE compared to the RF of the sum of the individual aerosol components. The spread in results for the individual aerosol components is substantial, and can be divided into diversities in burden, mass extinction coefficient (MEC), and normalized RF with respect to AOD. We find that these three factors give similar contributions to the spread in results.

DOI： 10.5194/acp-13-1853-2013

Language：English   Publishing type：Research paper (scientific journal)  

In this study, we assess changes of aerosol optical depth (AOD) and direct radiative forcing (DRF) in response to the reduction of anthropogenic emissions in four major pollution regions in the Northern Hemisphere by using results from nine global models in the framework of the Hemispheric Transport of Air Pollution (HTAP). DRF at top of atmosphere (TOA) and surface is estimated based on AOD results from the HTAP models and AOD-normalized DRF (NDRF) from a chemical transport model. The multimodel results show that, on average, a 20&#37; reduction of anthropogenic emissions in North America, Europe, East Asia, and South Asia lowers the global mean AOD (all-sky TOA DRF) by 9.2&#37; (9.0&#37;), 3.5&#37; (3.0&#37;), and 9.4&#37; (10.0&#37;) for sulfate, particulate organic matter (POM), and black carbon (BC), respectively. Global annual average TOA all-sky forcing efficiency relative to particle or gaseous precursor emissions from the four regions (expressed as multimodel mean±one standard deviation) is -3.5±0.8, -4.0±1.7, and 29.5±18.1mWm&lt
inf&gt
-2&lt
/inf&gt
per Tg for sulfate (relative to SO&lt
inf&gt
2&lt
/inf&gt
), POM, and BC, respectively. The impacts of the regional emission reductions on AOD and DRF extend well beyond the source regions because of intercontinental transport (ICT). On an annual basis, ICT accounts for 11±5&#37; to 31±9&#37; of AOD and DRF in a receptor region at continental or subcontinental scale, with domestic emissions accounting for the remainder, depending on regions and species. For sulfate AOD, the largest ICT contribution of 31±9&#37; occurs in South Asia, which is dominated by the emissions from Europe. For BC AOD, the largest ICT contribution of 28±18&#37; occurs in North America, which is dominated by the emissions from East Asia. The large spreads among models highlight the need to improve aerosol processes in models, and evaluate and constrain models with observations. © 2012. American Geophysical Union.

DOI： 10.1029/2012JD018148

Language：English   Publishing type：Research paper (scientific journal)  

We expanded the variational assimilation system of a regional dust model by using size-resolved inversion. Dust emissions and particle-size distributions of a severe dust and sandstorm (DSS) in April 2005 were inversely optimized with optical measurements by the National Institute for Environmental Studies lidar network. The inversion results successfully compensated underestimates by the original model and increased the Angstrom exponent around the DSS core by 13-17&#37;, shifting the particle-size distribution to finer. The a posteriori size distribution was distinctly different between eastern and western source regions. In the western regions, dust emissions in the 3.19 and 5.06 mu m size bins increased considerably, and the peak size shifted from 5.06 to 3.19 mu m, whereas in the eastern regions, emissions of finer particles (bins 0.82-2.01 mu m) increased. Differences in vegetation and soil type and moisture between eastern and western regions might explain the characteristics of the inverted size distribution. Citation: Yumimoto, K., I. Uno, N. Sugimoto, A. Shimizu, Y. Hara, and T. Takemura (2012), Size-resolved adjoint inversion of Asian dust, Geophys. Res. Lett., 39, L24807, doi: 10.1029/2012GL053890.

DOI： 10.1029/2012GL053890

Language：English   Publishing type：Research paper (scientific journal)  

Emissions of air pollutants and their precursors determine regional air quality and can alter climate. Climate change can perturb the long-range transport, chemical processing, and local meteorology that influence air pollution. We review the implications of projected changes in methane (CH4), ozone precursors (O3), and aerosols for climate (expressed in terms of the radiative forcing metric or changes in global surface temperature) and hemispheric-to-continental scale air quality. Reducing the O3 precursor CH4 would slow near-term warming by decreasing both CH4 and tropospheric O3. Uncertainty remains as to the net climate forcing from anthropogenic nitrogen oxide (NOx) emissions, which increase tropospheric O3 (warming) but also increase aerosols and decrease CH4 (both cooling). Anthropogenic emissions of carbon monoxide (CO) and non-CH4 volatile organic compounds (NMVOC) warm by increasing both O3 and CH4. Radiative impacts from secondary organic aerosols (SOA) are poorly understood. Black carbon emission controls, by reducing the absorption of sunlight in the atmosphere and on snow and ice, have the potential to slow near-term warming, but uncertainties in coincident emissions of reflective (cooling) aerosols and poorly constrained cloud indirect effects confound robust estimates of net climate impacts. Reducing sulfate and nitrate aerosols would improve air quality and lessen interference with the hydrologic cycle, but lead to warming. A holistic and balanced view is thus needed to assess how air pollution controls influence climate
a first step towards this goal involves estimating net climate impacts from individual emission sectors. Modeling and observational analyses suggest a warming climate degrades air quality (increasing surface O3 and particulate matter) in many populated regions, including during pollution episodes. Prior Intergovernmental Panel on Climate Change (IPCC) scenarios (SRES) allowed unconstrained growth, whereas the Representative Concentration Pathway (RCP) scenarios assume uniformly an aggressive reduction, of air pollutant emissions. New estimates from the current generation of chemistry–climate models with RCP emissions thus project improved air quality over the next century relative to those using the IPCC SRES scenarios. These two sets of projections likely bracket possible futures. We find that uncertainty in emission-driven changes in air quality is generally greater than uncertainty in climate-driven changes. Confidence in air quality projections is limited by the reliability of anthropogenic emission trajectories and the uncertainties in regional climate responses, feedbacks with the terrestrial biosphere, and oxidation pathways affecting O3 and SOA. © 2012 The Royal Society of Chemistry.

DOI： 10.1039/c2cs35095e

Language：English   Publishing type：Research paper (scientific journal)  

Numerical weather prediction (NWP) simulations using the Japan Meteorological Agency Nonhydrostatic Model (JMA-NHM) are conducted for three precipitation events observed by shipborne or spaceborne W-band cloud radars. Spectral bin and single-moment bulk cloud microphysics schemes are employed separately for an intercomparative study. A radar product simulator that is compatible with both microphysics schemes is developed to enable a direct comparison between simulation and observation with respect to the equivalent radar reflectivity factor Ze, Doppler velocity (DV), and path-integrated attenuation (PIA). In general, the bin model simulation shows better agreement with the observed data than the bulk model simulation. The correction of the terminal fall velocities of snowflakes using those of hail further improves the result of the bin model simulation. The results indicate that there are substantial uncertainties in the mass-size and size-terminal fall velocity relations of snowflakes or in the calculation of terminal fall velocity of snow aloft. For the bulk microphysics, the overestimation of Ze is observed as a result of a significant predominance of snow over cloud ice due to substantial deposition growth directly to snow. The DV comparison shows that a correction for the fall velocity of hydrometeors considering a change of particle size should be introduced even in single-moment bulk cloud microphysics.

DOI： 10.1175/JAS-D-11-0213.1

Language：English   Publishing type：Research paper (scientific journal)  

We present a numerical study carried out with the SPRINTARS model modified to account for the radioactive decay of S-35 compounds emitted from the Fukushima Daiichi nuclear power plant station after the hydrogen and vapor blast. The transport dynamics of the released material reproduced previous field observations. Four different emission scenarios were compared to the measurements of atmospheric S-35 in sulfate collected in La Jolla, Tsukuba, Kashiwa and Yokohama. Linear regressions of the relation between emitted and transported material that reached the sampling sites were used to estimate the amount of S-35 atoms and the amount of neutrons released in to the atmosphere. We estimate that a lower limit of 1.9 x 10(16) S-35 atoms sec(-1) were released after the events in March and this flux dropped to 4-39 x 10(14) S-35 atoms sec(-1) at the end of the month. Based on this calculations we estimated a lower limit of 5.2 x 10(21) slow neutrons m(-2) sec(-1) were emitted from the nuclear fuel rods to the sea water injected in the reactors after the events in March.

DOI： 10.2343/geochemj.2.0212

Language：English   Publishing type：Research paper (scientific journal)  

Emissions of air pollutants and their precursors determine regional air quality and can alter climate. Climate change can perturb the long-range transport, chemical processing, and local meteorology that influence air pollution. We review the implications of projected changes in methane (CH4), ozone precursors (O-3), and aerosols for climate (expressed in terms of the radiative forcing metric or changes in global surface temperature) and hemispheric-to-continental scale air quality. Reducing the O-3 precursor CH4 would slow near-term warming by decreasing both CH4 and tropospheric O-3. Uncertainty remains as to the net climate forcing from anthropogenic nitrogen oxide (NOx) emissions, which increase tropospheric O-3 (warming) but also increase aerosols and decrease CH4 (both cooling). Anthropogenic emissions of carbon monoxide (CO) and non-CH4 volatile organic compounds (NMVOC) warm by increasing both O-3 and CH4. Radiative impacts from secondary organic aerosols (SOA) are poorly understood. Black carbon emission controls, by reducing the absorption of sunlight in the atmosphere and on snow and ice, have the potential to slow near-term warming, but uncertainties in coincident emissions of reflective (cooling) aerosols and poorly constrained cloud indirect effects confound robust estimates of net climate impacts. Reducing sulfate and nitrate aerosols would improve air quality and lessen interference with the hydrologic cycle, but lead to warming. A holistic and balanced view is thus needed to assess how air pollution controls influence climate; a first step towards this goal involves estimating net climate impacts from individual emission sectors. Modeling and observational analyses suggest a warming climate degrades air quality (increasing surface O-3 and particulate matter) in many populated regions, including during pollution episodes. Prior Intergovernmental Panel on Climate Change (IPCC) scenarios (SRES) allowed unconstrained growth, whereas the Representative Concentration Pathway (RCP) scenarios assume uniformly an aggressive reduction, of air pollutant emissions. New estimates from the current generation of chemistry-climate models with RCP emissions thus project improved air quality over the next century relative to those using the IPCC SRES scenarios. These two sets of projections likely bracket possible futures. We find that uncertainty in emission-driven changes in air quality is generally greater than uncertainty in climate-driven changes. Confidence in air quality projections is limited by the reliability of anthropogenic emission trajectories and the uncertainties in regional climate responses, feedbacks with the terrestrial biosphere, and oxidation pathways affecting O-3 and SOA.

DOI： 10.1039/c2cs35095e

Language：English   Publishing type：Research paper (scientific journal)  

The historical anthropogenic change in the surface all-sky UV-B (solar ultraviolet: 280-315 nm) radiation through 1850-2005 is evaluated using an Earth system model. Responses of UV-B dose to anthropogenic changes in ozone and aerosols are separately evaluated using a series of historical simulations including/excluding these changes. Increases in these air pollutants cause reductions in UV-B transmittance, which occur gradually/rapidly before/after 1950 in and downwind of industrial and deforestation regions. Furthermore, changes in ozone transport in the lower stratosphere, which is induced by increasing greenhouse gas concentrations, increase ozone concentration in the extratropical upper troposphere and lower stratosphere. These transient changes work to decrease the amount of UV-B reaching the Earth's surface, counteracting the well-known effect increasing UV-B due to stratospheric ozone depletion, which developed rapidly after ca. 1980. As a consequence, the surface UV-B radiation change between 1850 and 2000 is negative in the tropics and NH extratropics and positive in the SH extratropics. Comparing the contributions of ozone and aerosol changes to the UV-B change, the transient change in ozone absorption of UV-B mainly determines the total change in the surface UV-B radiation at most locations. On the other hand, the aerosol direct and indirect effects on UV-B play an equally important role to that of ozone in the NH mid-latitudes and tropics. A typical example is East Asia (25A degrees N-60A degrees N and 120A degrees E-150A degrees E), where the effect of aerosols (ca. 70&#37;) dominates the total UV-B change.

DOI： 10.5194/acp-12-5249-2012

Language：English   Publishing type：Research paper (scientific journal)  

A synergy of satellite and ground-based radiometric observations, along with chemical transport modeling, was used for the assessment of the influence of drought monsoon conditions of 2002 and prolonged dry pre-monsoon period of 2003 on aerosol properties over south Asia, with emphasis over northern India. Reanalysis data are also examined for studying the dry anomalous period from the climatological mean, that show prevalence of westerlies under anticyclonic circulation and subsidence favoring the accumulation of aerosols. TRMM observations over south Asia indicate significant rainfall deficit over northwestern India in July 2002 and May-June 2003. Subsequently, the anomalous and prolonged dry conditions favored heavy aerosol buildup as indicated by strong positive anomalies (20-80&#37;) of MODIS aerosol optical depth (AOD) as well as significant increase in TOMS aerosol index (AI) during July 2002 and May-June 2003 compared to the long-term monthly means. The largest increase in aerosol loading is observed over northern India, encompassing the Indo-Gangetic Plains (IGP) that is in the downwind region of dust outflow from the Thar Desert and long-range transport from Arabia and Middle East. Ground-based sunphotometer observations at Delhi and Kanpur also show enhanced presence of desert-dust aerosols during July 2002 and May-June 2003, characterized by large AOD and significantly low Angstrom Exponent. In addition, modifications in columnar aerosol size distribution toward larger coarse-mode fraction and higher single scattering albedo at longer wavelengths were observed, thus supporting the observation of enhanced dust influx. SPRINTARS model simulations also show the enhanced dust loading over northern India during the studied months, which is in general agreement with the satellite and ground-based observations.

DOI： 10.1029/2011JD017314

Language：English   Publishing type：Research paper (scientific journal)  

The CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) layer product is used for a multimodel evaluation of the vertical distribution of aerosols. Annual and seasonal aerosol extinction profiles are analyzed over 13 sub-continental regions representative of industrial, dust, and biomass burning pollution, from CALIOP 2007-2009 observations and from AeroCom (Aerosol Comparisons between Observations and Models) 2000 simulations. An extinction mean height diagnostic (Z(alpha)) is defined to quantitatively assess the models' performance. It is calculated over the 0-6 km and 0-10 km altitude ranges by weighting the altitude of each 100 m altitude layer by its aerosol extinction coefficient. The mean extinction profiles derived from CALIOP layer products provide consistent regional and seasonal specificities and a low inter-annual variability. While the outputs from most models are significantly correlated with the observed Z(alpha) climatologies, some do better than others, and 2 of the 12 models perform particularly well in all seasons. Over industrial and maritime regions, most models show higher Z(alpha) than observed by CALIOP, whereas over the African and Chinese dust source regions, Za is underestimated during Northern Hemisphere Spring and Summer. The positive model bias in Z(alpha) is mainly due to an overestimate of the extinction above 6 km. Potential CALIOP and model limitations, and methodological factors that might contribute to the differences are discussed.

DOI： 10.1029/2011JD016858

Language：English   Publishing type：Research paper (scientific journal)  

Although aerosols have great impacts on Surface Downward Shortwave Flux (SDSF), the relationship between aerosol loading and SDSF in global models has not yet been adequately investigated. In this study, we attempt to investigate the effects of aerosol optical thickness (AOT) and single scattering albedo (SSA) on SDSF through an integrative analysis of modeling and observation. At first, we compared the results obtained by a global aerosol model, SPRINTARS, with in-situ measurements, AERONET and BSRN. And then we estimated the impacts of AOT and SSA on SDSF through an offline radiative transfer model, Rstar. Through this study, we found that the difference in SDSF between SPRINTARS and BSRN is much larger over heavy aerosol regions than those over regions. Using the Rstar radiative transfer model, we demonstrated that the AOT difference usually has the strongest impact on the SDSF difference and the SSA difference has a moderate impact over heavy aerosol loading regions, whereas the effect of water vapor can be ignored. Finally, we generated a contour plot to demonstrate the relationships between AOT-SSA-SDSF. For example, at low AOT (e.g., 0.15), the 20 W m(-2) changes in SDSF are required to make more than 0.2 changes of SSA, whereas at high AOT (e.g., 0.85), the same changes in SDSF are required to have only 0.05 changes of SSA. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2011.11.032

Language：Japanese   Publishing type：Research paper (scientific journal)  

Climate sensitivity Part 3: Verification from the past environment

Language：Japanese   Publishing type：Research paper (scientific journal)  

Climate sensitivity Part 2: Efforts toward reducing uncertainty

Language：Japanese   Publishing type：Research paper (scientific journal)  

Climate sensitivity Part 1: Concept and current understanding of climate feedbacks

Language：English   Publishing type：Research paper (scientific journal)  

The direct radiative forcing by sulfate aerosols is still uncertain, mainly because the uncertainties are largely derived from differences in sulfate column burdens and its vertical distributions among global aerosol models. One possible reason for the large difference in the computed values is that the radiative forcing delicately depends on various simplifications of the sulfur processes made in the models. In this study, therefore, we investigated impacts of different parts of the sulfur chemistry module in a global aerosol model, SPRINTARS, on the sulfate distribution and its radiative forcing. Important studies were effects of simplified and more physical-based sulfur processes in terms of treatment of sulfur chemistry, oxidant chemistry, and dry deposition process of sulfur components. The results showed that the difference in the aqueous-phase sulfur chemistry among these treatments has the largest impact on the sulfate distribution. Introduction of all the improvements mentioned above brought the model values noticeably closer to in-situ measurements than those in the simplified methods used in the original SPRINTARS model. At the same time, these improvements also brought the computed sulfate column burdens and its vertical distributions into good agreement with other AEROCOM model values. The global annual mean radiative forcing due to the direct effect of anthropogenic sulfate aerosol was thus estimated to be -0.26 W m(-2) (-0.30 W m(-2) with a different SO2 inventory), whereas the original SPRINTARS model showed -0.18 W m(-2) (-0.21 W m(-2) with a different SO2 inventory). The magnitude of the difference between original and improved methods was approximately 50&#37; of the uncertainty among estimates by the world's global aerosol models reported by the IPCC-AR4 assessment report. Findings in the present study, therefore, may suggest that the model differences in the simplifications of the sulfur processes are still a part of the large uncertainty in their simulated radiative forcings.

DOI： 10.5194/acp-11-10889-2011

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We developed a new ensemble-based data-assimilation system based on a global aerosol climate model and performed a 1-month assimilation experiment using satellite optical measurements from MODIS onboard TERRA and AQUA to estimate the direct radiative effect (DRE) of aerosols. Using the assimilated data field, monthly averaged optical thickness (AOT) was estimated to be 0.15 +/- 0.030 (a 52.0&#37; increase over a priori), and the root mean-square difference (RMSD) between modeled values and MODIS measurements was reduced by 28.4&#37;. Independent validation using globally distributed AERONET measurements showed that the a posteriori data achieved better agreement with 82.5&#37; of 80 AERONET sites. However, improvements in Angstrom exponents were limited (50.0&#37; of sites). Using the assimilated aerosol field, we modeled the aerosol DRE. A posteriori whole- and clear-sky DREs at the top of the atmosphere were estimated to be -1.1 +/- 0.35 and -2.5 +/- 0.49 W/m(2), respectively, in May 2007 and were close to previously reported measurement-based estimates. Citation: Yumimoto, K., and T. Takemura (2011), Direct radiative effect of aerosols estimated using ensemble-based data assimilation in a global aerosol climate model, Geophys. Res. Lett., 38, L21802, doi:10.1029/2011GL049258.

DOI： 10.1029/2011GL049258

Language：English   Publishing type：Research paper (scientific journal)  

An earth system model (MIROC-ESM 2010) is fully described in terms of each model component and their interactions. Results for the CMIP5 (Coupled Model Inter-comparison Project phase 5) historical simulation are presented to demonstrate the model's performance from several perspectives: atmosphere, ocean, sea-ice, land-surface, ocean and terrestrial biogeochemistry, and atmospheric chemistry and aerosols. An atmospheric chemistry coupled version of MIROC-ESM (MIROC-ESM-CHEM 2010) reasonably reproduces transient variations in surface air temperatures for the period 1850-2005, as well as the present-day climatology for the zonal-mean zonal winds and temperatures from the surface to the mesosphere. The historical evolution and global distribution of column ozone and the amount of tropospheric aerosols are reasonably simulated in the model based on the Representative Concentration Pathways' (RCP) historical emissions of these precursors. The simulated distributions of the terrestrial and marine biogeochemistry parameters agree with recent observations, which is encouraging to use the model for future global change projections.

DOI： 10.5194/gmd-4-845-2011

Language：English   Publishing type：Research paper (scientific journal)  

Key variables required for aerosol direct radiative forcing estimates are aerosol optical thickness (AOT), Angstrom Exponent (AE) and single scattering albedo (SSA), which are determined not only by aerosol amount but also by physical and optical parameters such as size distribution, hygroscopicity, mixing state of the particles, and refractive index especially of absorbing particles such as black carbon (BC) and dust. As the values of these parameters are often assumed in climate models, we investigate how the variations in these prescribed parameters can explain the differences in AOT, AE and SSA between the simulation by an aerosol global model and the ground-based remote sensing observation, AERONET. We conclude that the differences between our simulations and AERONET observations of AOT, AE and SSA are larger than sampling errors but can be generally explained by the uncertainty of the assumed parameters, although some simulations have clear biases that may be caused by errors in both emission and transport by the model. The uncertainty of sulfate sizes significantly dominates the uncertainty of AOT, AE and SSA, whereas the uncertainty of dust refractive indices and mixing states of organic carbon and BC is dominates the uncertainty of SSA. Citation: Goto, D., N. A. J. Schutgens, T. Nakajima, and T. Takemura (2011), Sensitivity of aerosol to assumed optical properties over Asia using a global aerosol model and AERONET, Geophys. Res. Lett., 38, L17810, doi: 10.1029/2011GL048675.

DOI： 10.1029/2011GL048675

Language：English   Publishing type：Research paper (scientific journal)  

We investigate the impacts of anthropogenic aerosols on a precipitation trend observed over tropical Africa during the austral summer in the twentieth century using an atmosphere-ocean general circulation model (medium-resolution version of the Model for Interdisciplinary Research on Climate (MIROC)). We conducted several numerical experiments forced with various combinations of natural and anthropogenic forcings. These experiments indicate that increased carbonaceous aerosols, especially black carbon (BC) aerosols, have played a vital role in the drying trend over tropical Africa, although increased sulfate aerosols contributed to the drying trend at the northern edge of the Intertropical Convergence Zone over tropical Africa. An analysis using an approximated moisture budget equation indicates that the increased carbonaceous aerosols cause the drying trend through an evaporation reduction and a descending anomaly over tropical Africa. The increases in BC and organic carbon aerosols enhance the absorption and scattering of solar radiation, respectively, resulting in reductions of the incident solar radiation, temperature, and evaporation at the surface. On the other hand, the absorption of solar radiation that is due to BC aerosols causes surrounding atmospheric heating in the lower troposphere, leading to an ascending anomaly over the tropical Atlantic Ocean. The ascending anomaly modulates the zonal atmospheric circulation in the Atlantic Ocean, tropical Africa, and the Indian Ocean, which drives a descending anomaly over tropical Africa. Similar atmospheric heating is observed over tropical Africa by atmospheric soundings during the austral summer in the late twentieth century, which supports our results. © 2011 by the American Geophysical Union.

DOI： 10.1029/2011JD015933

Language：English   Publishing type：Research paper (scientific journal)  

This study presents the results of a broad intercomparison of a total of 15 global aerosol models within the AeroCom project. Each model is compared to observations related to desert dust aerosols, their direct radiative effect, and their impact on the biogeochemical cycle, i.e., aerosol optical depth (AOD) and dust deposition. Additional com parisons to Angstrom exponent (AE), coarse mode AOD and dust surface concentrations are included to extend the assessment of model performance and to identify common biases present in models. These data comprise a benchmark dataset that is proposed for model inspection and future dust model development. There are large differences among the global models that simulate the dust cycle and its impact on climate. In general, models simulate the climatology of vertically integrated parameters (AOD and AE) within a factor of two whereas the total deposition and surface concentration are reproduced within a factor of 10. In addition, smaller mean normalized bias and root mean square errors are obtained for the climatology of AOD and AE than for total deposition and surface concentration. Characteristics of the datasets used and their uncertainties may influence these differences. Large uncertainties still exist with respect to the deposition fluxes in the southern oceans. Further measurements and model studies are necessary to assess the general model performance to reproduce dust deposition in ocean regions sensible to iron contributions. Models overestimate the wet deposition in regions dominated by dry deposition. They generally simulate more realistic surface concentration at stations downwind of the main sources than at remote ones. Most models simulate the gradient in AOD and AE between the different dusty regions. However the seasonality and magnitude of both variables is better simulated at African stations than Middle East ones. The models simulate the offshore transport of West Africa throughout the year but they overestimate the AOD and they transport too fine particles. The models also reproduce the dust transport across the Atlantic in the summer in terms of both AOD and AE but not so well in winter-spring nor the southward displacement of the dust cloud that is responsible of the dust transport into South America. Based on the dependency of AOD on aerosol burden and size distribution we use model bias with respect to AOD and AE to infer the bias of the dust emissions in Africa and the Middle East. According to this analysis we suggest that a range of possible emissions for North Africa is 400 to 2200 Tg yr(-1) and in the Middle East 26 to 526 Tg yr(-1)

DOI： 10.5194/acp-11-7781-2011

Language：English   Publishing type：Research paper (scientific journal)  

Results of comprehensive long-term simulations of surface all-sky and clear-sky ultraviolet (UV) radiation through 1960-2100 are presented. A new earth system model, MIROC-ESM-CHEM, is used for the simulation, which considers key processes that change the surface UV radiation: atmospheric dynamics and chemistry affecting ozone in the stratosphere and troposphere, aerosols and clouds in the troposphere, and changes in surface albedo with sea ice and snow cover. In contrast to previous assessments considering only the effect of long-term change in stratospheric ozone, the simulated long-term behavior of UV radiation in this study is strongly affected by other processes. In one of two simulations, all-sky UV radiation in the northern midlatitudes is projected to increase in the 21st century despite the expected recovery of the stratospheric ozone layer. Reductions in aerosols and clouds are expected to overcompensate for the effect of ozone recovery. The results are sensitive to the future socioeconomic scenario, describing GHG concentrations and emissions of aerosol and ozone precursors in the troposphere. The interannual variability of UV radiation associated with the 11 year solar cycle and local processes is also discussed. Copyright © 2011 by the American Geophysical Union.

DOI： 10.1029/2011JD015749

Language：English   Publishing type：Research paper (scientific journal)  

The NASA space-borne Mie-lidar system CALIPSO/CALIOP revealed that multiple large Asian dust layers with a horizontal scale of 2000-3000 km reached North America, occupying the full troposphere, in April 2010. This kind of dust layer transport has not been reported before. Our analysis of CALIOP data and global aerosol model results revealed that frequent dust emissions occurred in northwestern China because of stronger-than-average near-surface winds, and that strong stable westerly winds carried the Asian dust from northwestern China to the central Pacific Ocean. A negative pressure anomaly was located in the eastern Pacific Ocean, and the main dust transport path was split into two branches: a northern path and a southern path over North America. Northern-path dust was trapped and stagnant for a longer time than southern path dust and finally subsided under a high-pressure system. Dust along the southern path reached the central US. These complex conditions resulted in a multi-layered structure of dust over North America.

DOI： 10.5194/acp-11-7333-2011

Language：English   Publishing type：Research paper (scientific journal)  

Mount Kilauea in the Hawaiian Islands experienced an active eruption from March until the end of December 2008 and showed a large-scale impact on aerosol, cloud microphysical properties and atmospheric radiation over the North Pacific. We analyzed the atmospheric impact of this eruption based on the satellite retrievals and 3-D global chemistry-radiation coupled transport model. We showed that approximately 1.8 Tg (+/- 1.2 Tg) release of SO2 was estimated from this eruption, which oxidized into sulfate aerosol during transport to the northwest Pacific Ocean. The volcanic sulfate aerosol layer covering a large area (similar to 6.5 x 10(6) km(2)) of the lower troposphere over the North Pacific for several months was confirmed from both satellite and model results. Sulfate aerosols affected the formation of cumulus water clouds by reducing the typical cloud effective radius by similar to 23&#37; and increasing the cloud fractional coverage over the ocean from 9.1&#37; to 13.4&#37; (over the region 170 degrees E-160 degrees W, 10 degrees N-20 degrees N). The affected cumulus clouds appeared whiter than normal and thus reflected more solar radiation. Consequently, satellite observations revealed an approximately 1&#37; increase in albedo at the top of the atmosphere in the area along main volcano plume trajectory, which induced an approximately -5 W m(-2) change in the shortwave radiation budget.

DOI： 10.2151/sola.2011-020

Language：English   Publishing type：Research paper (scientific journal)  

Black carbon (BC) aerosols through their light-absorbing properties create strong perturbation in the atmosphere by heating the atmosphere. BC mass concentration and single scattering albedo (SSA) are important parameters to investigate atmospheric heating. In the present study, measurements of BC and SSA over Indian region from the literature are summarized and compared with simulations by a global aerosol model SPRINTARS. It has been observed that BC emission inventory widely used in the world is underestimating and the model simulated SSA tends to be higher than observed-SSA. In addition to the inventory, we have run the global model using the different BC emission inventory interpolated by Streets et al. (2003) over Asia. The model runs with this inventory was found to provide comparable results with ground observations for BC and SSA. Aerosol radiative forcing due to direct effect (ADRF) over Indian region estimated to be -2.76 W m(-2) at the surface and -1.91 W m(-2) at the atmosphere using the modified emission inventory in the global aerosol model. The atmospheric heating is estimated to be +0.85 W m(-2), which is three times higher than the original emission inventory estimated value of +0.25 W m(-2). Results of the study suggest that the differences in various BC emission inventories widely used in the world's research community should be studied for proper estimation of the aerosol radiative forcing over the Indian region. (C) 2011 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2011.03.037

Language：English   Publishing type：Research paper (scientific journal)  

Summertime phytoplankton blooms in the oligotrophic North Pacific Ocean are supported by N-2-fixing organisms that relieve the system of nitrate limitation. Phosphate and iron, however, limit their growth and need to be supplied for these organisms to thrive. We analyze two recent blooms in the region whose differences provide insight into their possible formation mechanisms. In 2008, a typical late summer bloom, with sporadic patches of higher-chlorophyll concentration, occurred near the island chain and the subtropical front. In 2010, an unusually large, contiguous bloom was observed in the western oligotrophic North Pacific, a region where blooms seldom, if ever, occur. Streaks of high chlorophyll in 2008 coincide with surface temperature fronts and regions of large horizontal stretching, as detected by Lagrangian diagnostics. Such regions are prone to the generation of vertical velocities via frontogenesis. Horizontal transport from upwelling regions or iron-rich island sediments is also important for the redistribution of nutrients. In the case of the 2010 bloom, we use a global aerosol transport model as well as space-borne lidar observations to argue that atmospheric dust deposition events prior to the bloom provided the necessary nutrient conditions for the growth of N-2-fixing organisms. As sea surface temperature increased in the region, chlorophyll values increased significantly, showing that this bloom was likely a consequence of prior enrichment and that temperature is a key factor in bloom development in this important biome.

DOI： 10.1029/2010JC006704

Language：English   Publishing type：Research paper (scientific journal)  

Aerosols have great impacts on atmospheric environment, human health, and earth's climate. Therefore, information on their spatial and temporal distribution is of paramount importance. Despite numerous studies have examined the variation and trends of BC and AOD over India, only very few have focused on their spatial distribution or even correlating the observations with model simulations. In the present study, a three-dimensional aerosol transport-radiation model coupled with a general circulation model. SPRINTARS, simulated atmospheric aerosol distributions including BC and aerosol optical properties, i.e., aerosol optical thickness (AOT), Angstrom Exponent (AE), and single scattering albedo (SSA). The simulated results are compared with both BC measurements by aethalometer and aerosol optical properties measured by ground-based skyradiometer and by satellite sensor, MODIS/Terra over Hyderabad, which is a tropical urban area of India, for the year 2008. The simulated AOT and AE in Hyderabad are found to be comparable to ground-based measured ones. The simulated SSA tends to be higher than the ground-based measurements. Both these comparisons of aerosol optical properties between the simulations with different emission inventories and the measurements indicate that, firstly the model uncertainties derived from aerosol emission inventory cannot explain the gaps between the simulations and the measurements and secondly the vertical transport of BC and the treatment of BC-containing particles can be the main issue in the global model to solve the gap.

DOI： 10.5194/angeo-29-955-2011

Language：English   Publishing type：Research paper (scientific journal)  

Atmospheric aerosols are important aspects of climate research due to their impact on radiative forcing. In the present study, the aerosol optical depth (ADD), the Angstrom exponent (alpha) and the single scattering albedo (SSA) over the urban region of Hyderabad, India, were examined using Sun/Sky radiometer measurements during January-December, 2008. AOD showed higher values on certain Julian days coinciding with the occurrence of wintertime dust storm events in the Gulf Region and biomass burning due to forest fires over Indian Region. The AOD values during wintertime dust event are about similar to 55&#37; higher than those on normal days. The SSAs show positive and negative trends in alpha (R-2 = 0.71) and black carbon (BC) aerosols (R-2 = 0.44), respectively. The aerosol size distribution shows a bimodal pattern with fine (similar to 0.15 mu m) and coarse (similar to>7 mu m) mode during January-December, 2008. The MODIS AOD showed positive correlation with sky radiometer-derived AOD values (R-2 = 0.68). (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.atmosres.2011.01.003

Language：English   Publishing type：Research paper (scientific journal)  

We use global models to explore the microphysical effects of carbonaceous aerosols on liquid clouds. Although absorption of solar radiation by soot warms the atmosphere, soot may cause climate cooling due to its contribution to cloud condensation nuclei (CCN) and therefore cloud brightness. Six global models conducted three soot experiments; four of the models had detailed aerosol microphysical schemes. The average cloud radiative response to biofuel soot (black and organic carbon), including both indirect and semi-direct effects, is -0.11 Wm(-2), comparable in size but opposite in sign to the respective direct effect. In a more idealized fossil fuel black carbon experiment, some models calculated a positive cloud response because soot provides a deposition sink for sulfuric and nitric acids and secondary organics, decreasing nucleation and evolution of viable CCN. Biofuel soot particles were also typically assumed to be larger and more hygroscopic than for fossil fuel soot and therefore caused more negative forcing, as also found in previous studies. Diesel soot (black and organic carbon) experiments had relatively smaller cloud impacts with five of the models <+/- 0.06 Wm(-2) from clouds. The results are subject to the caveats that variability among models, and regional and interrannual variability for each model, are large. This comparison together with previously published results stresses the need to further constrain aerosol microphysical schemes. The non-linearities resulting from the competition of opposing effects on the CCN population make it difficult to extrapolate from idealized experiments to likely impacts of realistic potential emission changes.

DOI： 10.5194/acp-11-1051-2011

Language：English   Publishing type：Research paper (scientific journal)  

A new version of the atmosphere ocean general circulation model cooperatively produced by the Japanese research community known as the Model for Interdisciplinary Research on Climate (MIROC) has recently been developed A century long control experiment was performed using the new version (MIROC5) with the standard resolution of the T85 atmosphere and 1 degrees ocean models The climatological mean state and variability are then compared with observations and those in a previous version (MIROC3 2) with two different resolutions (medres hires) coarser and finer than the resolution of MIROC5
A few aspects of the mean fields in MIROC5 are similar to or slightly worse than MIROC3 2 but otherwise the climatological features are considerably better In particular improvements are found in precipitation zonal mean atmospheric fields equatorial ocean subsurface fields and the simulation of El Nino-Southern Oscillation The difference between MIROC5 and the previous model is larger than that between the two MIROC3 2 versions indicating a greater effect of updating parameterization schemes on the model climate than increasing the model resolution The mean cloud property obtained from the sophisticated prognostic schemes in MIROC5 shows good agreement with satellite measurements MIROC5 reveals an equilibrium climate sensitivity of 2 6 K which is lower than that in MIROC3 2 by 1 K This is probably due to the negative feedback of low clouds to the increasing concentration of CO2 which is opposite to that in MIROC3 2

DOI： 10.1175/2010JCLI3679.1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2010GL045530

Language：English   Publishing type：Research paper (scientific journal)  

Springtime outflow of Asian dust and air pollutants was investigated by a synergetic analysis of ground-based/space-borne Lidar observations and numerical models. We identified two prominent outflow patterns, and its occurrence frequency. Pattern I was induced within a typical warm-sector which lifted up dust particles into the free troposphere, and the existence of two sequential low-pressure systems played an important role. Pattern II was a 'behind cold front' outbreak. Atmospheric stratification was significantly different; Pattern I had weak stratification within the troposphere (potential temperature gradient of similar to 2-3.4 K/km), and most of elevated dust layer (typically horizontally 1500-2000 km, vertically 2.5-4 km AGL) remained unmixed with pollutants. Pattern II was characterized by a strong stratification of similar to 5 K/km; dust and pollutants were trapped and well mixed within the PBL, forming 'polluted' dust. Among the six cases of large-scale dust/pollutants outbreaks, only two cases are belonged to Pattern I. Citation: Itahashi, S., K. Yumimoto, I. Uno, K. Eguchi, T. Takemura, Y. Hara, A. Shimizu, N. Sugimoto, and Z. Liu (2010), Structure of dust and air pollutant outflow over East Asia in the spring, Geophys. Res. Lett., 37, L20806, doi:10.1029/2010GL044776.

DOI： 10.1029/2010GL044776

Language：English   Publishing type：Research paper (scientific journal)  

The distances over which localized radiative forcing influences surface temperature have not been well characterized. We present a general methodology to analyze the spatial scales of the forcing/response relationship and apply it to simulations of historical aerosol forcing and response in four climate models. We find that the surface temperature response is not strongly sensitive to the longitude of forcing but is fairly sensitive to latitude. Surface temperature responses in the Arctic and the Southern Hemisphere extratropics, where forcing was small, show little relationship to local forcing. Restricting the analysis to 30°S-60°N, where nearly all the forcing was applied, shows that forcing strongly influences response out to ∼4500 km away examining all directions. The meridional length of influence is somewhat shorter (∼3500 km or 30°), while it extends out to at least 12,000 km in the zonal direction. Substantial divergences between the models are seen over the oceans, whose physical representations differ greatly among the models. Length scales are quite consistent over 30°S-60°N land areas, however, despite differences in both the forcing applied and the physics of the models themselves. The results suggest that better understanding of regionally inhomogeneous radiative forcing would lead to improved projections of regional climate change over land areas. They also provide quantitative estimates of the spatial extent of the climate impacts of pollutants, which can extend thousands of kilometers beyond polluted areas, especially in the zonal direction. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2010JD014108

Language：English   Publishing type：Research paper (scientific journal)  

Levoglucosan is considered as a useful molecular tracer of biomass-burning aerosols in the atmosphere. To characterize the seasonal variation of its concentrations over the Pacific Ocean and to assess its usefulness as a tracer after long-range transport, we investigated long-term variations of levoglucosan over Chichi-jima in the western North Pacific, from 2001 to 2004. Organic carbon (OC), elemental carbon (EC) and D-glucose were analyzed for comparison. The seasonal variation of levoglucosan concentrations showed a maximum in the winter, which is consistent with the enhanced Asian outflow to the Pacific indicated by backward air-mass trajectories. The concentration levels of levoglucosan estimated from global aerosol model outputs in the winter are, on average, comparable to the observed levels, suggesting that a considerable fraction of levoglucosan did not decompose during long-range transport from the Asian continent by westerly/northwesterly winds. This result is supported by comparable ratios of levoglucosan to EC in Chichi-jima and the East Asian coastal region. Conversely, the measured concentrations of levoglucosan in the summer were significantly lower than the modeled one. This implies a degradation of levoglucosan in the air masses that stagnated over the Pacific, although uncertainties in the model estimate may also be partly responsible for this discrepancy. One possible degradation pathway is oxidation by OH radicals; the contribution of acid-catalyzed reactions needs further investigation. (C) 2010 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.atmosenv.2010.06.017

Language：English   Publishing type：Research paper (scientific journal)  

In mid-August 2009, ground-based lidar networks on both sides of the Pacific Basin detected an elevated dust layer. A combined analysis by ground-based lidars, spaceb-orne lidar CALIOP, and numerical models revealed that dust particles emitted in the Taklimakan Desert were transported across the Pacific Ocean in 12 to 13 days. This was the first evidence of summertime trans-Pacific transport of Asian dust from the Taklimakan Desert. A large-scale dust storm occurred in the Taklimakan Desert during 12-16 August due to a strong surface wind accompanied by a cold front. Many dust particles were lifted up into the free atmosphere by the upslope wind formed by the steep slope of the surrounding mountains. This dust injection process was analogous to that for springtime cases. The Taklimakan dust was then transported eastward at 6-8 km altitude. This high transport altitude allowed the Taklimakan Dust to be transported beyond the Pacific Ocean without the effect of the southeasterly outflow of the summertime Pacific high. The wind field anomaly at 500 hPa in mid-August 2009 shows increases of northwesterly winds driven by SE-NW pressure gradients around 110-140 degrees E and 180-140 degrees W, indicating that the pressure pattern during the dust event favored the trans-Pacific transport.
Citation: Yumimoto, K., K. Eguchi, I. Uno, T. Takemura, Z. Liu, A. Shimizu, N. Sugimoto, and K. Strawbridge (2010), Summertime trans-Pacific transport of Asian dust, Geophys. Res. Lett., 37, L18815, doi:10.1029/2010GL043995.

DOI： 10.1029/2010GL043995

Language：English   Publishing type：Research paper (scientific journal)  

This study analyzed 95-GHz radar/lidar data collected from the R/V Mirai over the tropical western Pacific to characterize the vertical distribution of ice cloud effective radius r&lt
inf&gt
eff&lt
/inf&gt
, ice water content IWC, and in-cloud vertical velocity of the region in conjunction with weather regimes classified by International Satellite Cloud Climatology Project (ISCCP) cluster analysis. Ice clouds observed from the Mirai were roughly consistent with the ISCCP weather regimes
more convectively active regimes had larger amounts of high cloud consisting of deeper cloud with larger ice water path (IWP) and precipitating ice fraction. Ice cloud microphysics of the Center for Climate System Research, National Institute for Environmental Studies, Frontier Research Center for Global Change atmospheric general circulation model (AGCM) was then evaluated using the radar-lidar simulator and ISCCP weather regimes for comparison of the statistics at different scales. The model tended to produce a high cloud fraction that was two times larger in the cirrus regimes but 50% lower in the deepest convective regime. The simulated IWP could only weakly reproduce the observed variety and generally underestimated the observed values despite the weather regimes. Cutoff in the simulated grid mean IWC around 0.1 g&lt
sup&gt
-3&lt
/sup&gt
was too small, especially above 11 km. The AGCM successfully predicted the observed frequency distribution for r&lt
inf&gt
eff&lt
/inf&gt
above 11 km, but produced large overestimation in the peak value below 11 km due to the excessively large fraction of r&lt
inf&gt
eff&lt
/inf&gt
∼100 m. Establishing a cutoff for cloud ice at r&lt
inf&gt
eff&lt
/inf&gt
&gt
120 m was found to be quite reasonable, although it would miss some of the larger particles that were observed. Copyright 2010 by the American Geophysical Union.

DOI： 10.1029/2009JD012944

Language：English   Publishing type：Research paper (scientific journal)  

We present sensitivity tests for a global aerosol assimilation system utilizing AERONET observations of AOT (aerosol optical thickness) and AAE (aerosol Angstrom exponent). The assimilation system employs an ensemble Kalman filter which requires tuning of three numerical parameters: ensemble size n(ens), local patch size n(patch) and inflation factor rho. In addition, experiments are performed to test the impact of various implementations of the system. For instance, we use a different prescription of the emission ensemble or a different combination of observations.
The various experiments are compared against one-another and against independent AERONET and MODIS/Aqua observations. The assimilation leads to significant improvements in modelled AOT and AAE fields. Moreover remaining errors are mostly random while they are mostly systematic for an experiment without assimilation. In addition, these results do not depend much on our parameter or design choices.
It appears that the value of the local patch size has by far the biggest impact on the assimilation, which has sufficiently converged for an ensemble size of n(ens) = 20. Assimilating AOT and AAE is clearly preferential to assimilating AOT at two different wavelengths. In contrast, initial conditions or a description of aerosol beyond two modes (coarse and fine) have only little effect.
We also discuss the use of the ensemble spread as an error estimate of the analysed AOT and AAE fields. We show that a very common prescription of the emission ensemble (independent random modification in each grid cell) can have trouble generating sufficient spread in the forecast ensemble.

DOI： 10.5194/acp-10-6583-2010

Language：English   Publishing type：Research paper (scientific journal)  

The precipitation sensitivity per 1 K of global warming in twenty-first-century climate projections is smaller in an emission scenario with larger greenhouse gas concentrations and aerosol emissions, according to the Model for Interdisciplinary Research on Climate 3.2 (MIROC3.2) coupled atmosphere-ocean general circulation model. The authors examined the reasons for the precipitation sensitivity to emission scenarios by performing separated individual forcing runs under high and low emission scenarios. It was found that the dependency on emission scenario is mainly caused by differences in black and organic carbon aerosol forcing (the sum of which is cooling forcing) between the emission scenarios and that the precipitation is more sensitive to carbon aerosols than well-mixed greenhouse gases. They also investigated the reason for the larger precipitation sensitivity (larger magnitude of precipitation decrease per 1 K cooling of temperature) in the carbon aerosol runs. Surface dimming due to the direct and indirect effects of carbon aerosols effectively decreases evaporation and precipitation, which enhances the precipitation sensitivity in the carbon aerosol runs. In terms of the atmospheric moisture cycle, although changes of vertical circulation offset the effects of changes in the atmospheric moisture in both the carbon aerosol and greenhouse gas runs, the amplitude of vertical circulation change per 1 K temperature change is less in the carbon aerosol runs. Furthermore, the second indirect effect of organic carbon aerosol counteracts the influence of the vertical circulation change. These factors lead to suppression of changes in the moisture's atmospheric residence time and increase of the precipitation sensitivity in the carbon aerosol runs.

DOI： 10.1175/2009JCLI3428.1

Language：English   Publishing type：Research paper (scientific journal)  

Based on an approximated moisture budget equation, we investigate the physical mechanisms of a drying trend observed over tropical North Africa in the boreal summer during the 20th Century by analyzing datasets of several climate-model experiments forced with various combinations of natural and anthropogenic forcings. Increased anthropogenic aerosols thermodynamically induce a drying trend due to a tropospheric cooling and dynamically induce an additional drying trend due to an atmospheric local circulation change stirred up by the strong gradient of a sea surface temperature anomaly over the tropical Atlantic Ocean. Increased greenhouse gases, on the other hand, induce a drying trend through the large-scale dynamic effect, which is canceled out by the thermodynamically induced moistening trend due to tropospheric warming. Therefore, the drying trend observed over tropical North Africa during the 20th Century is strongly affected by the increased anthropogenic aerosols through both the dynamic and thermodynamic effects. Citation: Kawase, H., M. Abe, Y. Yamada, T. Takemura, T. Yokohata, and T. Nozawa (2010), Physical mechanism of long term drying trend over tropical North Africa, Geophys. Res. Lett., 37, L09706, doi: 10.1029/2010GL043038.

DOI： 10.1029/2010GL043038

Language：English   Publishing type：Research paper (scientific journal)  

Anthropogenic global warming will lead to changes in the global hydrological cycle. The uncertainty in precipitation sensitivity per 1 K of global warming across coupled atmosphere-ocean general circulation models (AOGCMs) has been actively examined. On the other hand, the uncertainty in precipitation sensitivity in different emission scenarios of greenhouse gases (GHGs) and aerosols has received little attention. Here we show a robust emission-scenario dependency (ESD); smaller global precipitation sensitivities occur in higher GHG and aerosol emission scenarios. Although previous studies have applied this ESD to the multi-AOGCM mean, our surprising finding is that current AOGCMs all have the common ESD in the same direction. Different aerosol emissions lead to this ESD. The implications of the ESD of precipitation sensitivity extend far beyond climate analyses. As we show, the ESD potentially propagates into considerable biases in impact assessments of the hydrological cycle via a widely used technique, so-called pattern scaling. Since pattern scaling is essential to conducting parallel analyses across climate, impact, adaptation and mitigation scenarios in the next report from the Intergovernmental Panel on Climate Change, more attention should be paid to the ESD of precipitation sensitivity.

DOI： 10.1007/s10584-009-9765-1

Language：Japanese   Publishing type：Research paper (scientific journal)  

Coupled effects of land use and aerosols changes and their impacts on Asian climate
This study assesses the roles of aerosols in the past/present changes in Asian climate and monsoon, isolating impacts of individual aerosol components in the framework of the CCSR/NIES/FRCGC climate model (MIROC). Many recent studies suggest that increases in anthropogenic aerosols such as black carbon and sulfate may play a crucial role in Asian climate change as observed. Our previous studies also demonstrate the significance of aerosol increases (sulfate and carbonaceous aerosols) in the simulated precipitation changes in Asia (e.g., Arai et al., 2009). In this study, we particularly focus on the changes of nitrate and secondary organic aerosols (SOA) which are tightly linked to land use change in regions like Asia, but not treated in our previous aerosol studies. We newly introduced simulation of nitrate aerosol in our climate model. Our simulation shows that there are anomalously high concentrations of nitrate aerosol in South Asia (particularly around India and Bangladesh), coming from abundant ammonium and less sulfate components in this region. In India, free tropospheric mixing ratio and number concentration of nitrate in fine mode are both larger than those of sulfate in

Language：English   Publishing type：Research paper (scientific journal)  

The distribution of N-2 fixation was examined using a N-15(2) tracer with accompanying measurements of abundance of Trichodesmium spp. and Richelia intracellularis, nitrate plus nitrite (N+N) and soluble reactive phosphorus at the nanomolar level, and primary production in the western and central Pacific Ocean. N-2 fixation occurred only in >similar to 20 degrees C oligotrophic (i.e., N+N < 100 nM) waters except at a station in the equatorial upwelling zone where N+N was 1880 nM. High N-2 fixation rates were observed in the Kuroshio and East China Sea (KECS) and near Fiji and other isolated islands with concomitant high abundance of Trichodesmium spp. In contrast, N-2 fixation in the western and central oligotrophic North Pacific (WCONP) was significantly lower, and Trichodesmium spp. were rarely observed. These observations hint that KECS and waters around isolated islands are N-2 fixation "hot spots" because of the occurrence of Trichodesmium spp. The average N2 fixation rate in the KECS of 232 +/- 54.8 (+/- SE, n=13) mu mol N m(-2) d(-1) was almost 1 order of magnitude higher than that in the WCONP of 39.2 +/- 7.51 +/- (n = 26) mu mol N m(-2) d(-1). On the basis of these estimates and reported values obtained using N-15(2), depth-integrated N-2 fixation in the North Pacific was estimated to be 2.6 +/- 0.3 x 109 (n = 63) mol N d(-1), which is less than half of previous estimates. This difference was ascribed primarily to the unavailability of N-2 fixation rates in the WCONP, which occupies a vast area of the subtropical North Pacific, and the use of data obtained in the hot spots which represent small areas that likely led to the previous overestimation.

DOI： 10.1029/2009GB003620

Language：English   Publishing type：Research paper (scientific journal)  

We present a global aerosol assimilation system based on an Ensemble Kalman filter, which we believe leads to a significant improvement in aerosol fields. The ensemble allows realistic, spatially and temporally variable model covariances (unlike other assimilation schemes). As the analyzed variables are mixing ratios (prognostic variables of the aerosol transport model), there is no need for the extra assumptions required by previous assimilation schemes analyzing aerosol optical thickness (AOT).
We describe the implementation of this assimilation system and in particular the construction of the ensemble. This ensemble should represent our estimate of current model uncertainties. Consequently, we construct the ensemble around randomly modified emission scenarios.
The system is tested with AERONET observations of AOT and Angstrom exponent (AE). Particular care is taken in prescribing the observational errors. The assimilated fields (AOT and AE) are validated through independent AERONET, SKYNET and MODIS Aqua observations. We show that, in general, assimilation of AOT observations leads to improved modelling of global AOT, while assimilation of AE only improves modelling when the AOT is high.

DOI： 10.5194/acp-10-2561-2010

Language：Others  

DOI： 10.5194/acp-10-79-2010

Language：Japanese   Publishing type：Research paper (scientific journal)  

Data Assimilation with Aerosol Transport Model
Data assimilation has been developed in numerical weather prediction (NWP) and modeling of oceanography. Recently, store and expansion of observations and development of numerical modeling have enabled data assimilation techniques to be applied to aerosol transport models. In this paper, we introduce information about applications (e.g., forecast, inverse modeling, reanalysis, sensitivity analysis) and recent studies about data assimilation with atmospheric aerosol observations and numerical models. We also show a preliminary experiment of ensemble-based data assimilation with global aerosol climate model (SPRINTARS) and Aerosol Optical Thickness (AOT) measured by MODIS/AQUA. In the experiment, the data assimilation improves under-estimates in East Asia, North Pacific Ocean, Central America, Middle East and Central Africa, and over-estimates in oceans over the southern hemisphere. Root mean square difference (RMSD) between SPRINTARS and MODIS AOT is reduced by 21 &#37;, and long-wave aerosol direct forcing at the tropopause increased where dust and carbon aerosol are increased by the data assimilation.

DOI： 10.11203/jar.24.256

Language：Others  

Introduction to the Feature Articles: Studies on Reducing Uncertainties of Estimation of Aerosol Effects on Climate System

DOI： 10.11203/jar.24.236

Language：Japanese   Publishing type：Research paper (scientific journal)  

Review and Future Studies of Estimating Aerosol Effects on Climate System
The aerosol effects on the climate system are roughly divided into three categories: direct, indirect, and semi-direct effects. Observations from satellites and ground with remote sensing and numerical models have been developed to understand and estimate aerosol effects on a global scale. In the latest assessment report of the Intergovernmental Panel on Climate Change (IPCC) , however, there are still large uncertainties in their radiative forcings in comparison with the estimation of long-lived greenhouse gases. To reduce the uncertainties, we have to study the three-dimensional aerosol distributions and the cloud-aerosol interaction more accurately. It is important to observe aerosol vertical profiles with lidar, one of the active sensors, to understand the three-dimensional aerosol distributions as well as to continue observations with passive sensors. The data assimilation, which harmonizes numerical models with observations, is also an effective method to reduce the uncertainties. A cloud resolving model coupled with an aerosol transport model is a useful tool to better understand the cloud-aerosol interaction. Efforts to analyze the aerosol climate effects quantitatively will result in more reliable projection of the future climate change and elucidating climate system.

DOI： 10.11203/jar.24.237

Language：English   Publishing type：Research paper (scientific journal)  

An intense dust storm occurred during 1920 May 2007 over the Taklimakan Desert in northwestern China. Over the following days, the space-borne lidar CALIOP tracked an optically thin, highly elevated, horizontally extensive dust veil that was transported intercontinentally over eastern Asia, the Pacific Ocean, North America, and the Atlantic Ocean. A global aerosol transport model (SPRINTARS) simulated the dust veil quite well and provided a three-dimensional view of the intercontinental dust transport. The SPRINTARS simulation revealed that the dust veil traveled at 4-10 km altitudes with a thickness of 1-4 km along the isentropic surface between 310 and 340 K. The transport speed was about 1500 km/day. The estimated dust amount exported to the Pacific was 30.8 Gg, of which 65&#37; was deposited in the Pacific and 18&#37; was transported to the North Atlantic. These results imply that dust veils can fertilize open oceans, add to background dust, and affect the radiative budget at high altitudes through scattering and absorption.
The injection mechanism that lifts dust particles into the free atmosphere is important for understanding the formation of the dust veil and subsequent long-range transport. We used a regional dust transport model (RC4) to analyze the dust emission and injection over the source region. The RC4 analysis revealed that strong northeasterly surface winds associated with low pressures invaded the Taklimakan Desert through the eastern corridor. These winds then formed strong upslope wind along the high, steep mountainsides of the Tibetan Plateau and blew large amounts of dust into the air. The updraft lifted the dust particles farther into the upper troposphere (about 9 km above mean sea level, MSL), where westerlies are generally present. The unusual terrain surrounding the Taklimakan Desert played a key role in the injection of dust to the upper troposphere to form the dust veil.

DOI： 10.5194/acp-9-8545-2009

Language：English   Publishing type：Research paper (scientific journal)  

We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) retrievals from AERONET and Ozone Monitoring Instrument (OMI) and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.7 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50N, the average model is a factor of 8 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC ratio is 0.4 and models underestimate the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models.

DOI： 10.5194/acp-9-9001-2009

Language：English   Publishing type：Research paper (scientific journal)  

Aerosol indirect effects continue to constitute one of the most important uncertainties for anthropogenic climate perturbations. Within the international AEROCOM initiative, the representation of aerosol-cloud-radiation interactions in ten different general circulation models (GCMs) is evaluated using three satellite datasets. The focus is on stratiform liquid water clouds since most GCMs do not include ice nucleation effects, and none of the model explicitly parameterises aerosol effects on convective clouds. We compute statistical relationships between aerosol optical depth (tau(a)) and various cloud and radiation quantities in a manner that is consistent between the models and the satellite data. It is found that the model-simulated influence of aerosols on cloud droplet number concentration (N-d) compares relatively well to the satellite data at least over the ocean. The relationship between tau(a) and liquid water path is simulated much too strongly by the models. This suggests that the implementation of the second aerosol indirect effect mainly in terms of an autoconversion parameterisation has to be revisited in the GCMs. A positive relationship between total cloud fraction (f(cld)) and tau(a) as found in the satellite data is simulated by the majority of the models, albeit less strongly than that in the satellite data in most of them. In a discussion of the hypotheses proposed in the literature to explain the satellite-derived strong f(cld)-tau(a) relationship, our results indicate that none can be identified as a unique explanation. Relationships similar to the ones found in satellite data between tau(a) and cloud top temperature or outgoing long-wave radiation (OLR) are simulated by only a few GCMs. The GCMs that simulate a negative OLR-tau(a) relationship show a strong positive correlation between tau(a) and f(cld). The short-wave total aerosol radiative forcing as simulated by the GCMs is strongly influenced by the simulated anthropogenic fraction of tau(a), and parameterisation assumptions such as a lower bound on N-d. Nevertheless, the strengths of the statistical relationships are good predictors for the aerosol forcings in the models. An estimate of the total short-wave aerosol forcing inferred from the combination of these predictors for the modelled forcings with the satellite-derived statistical relationships yields a global annual mean value of -1.5 +/- 0.5 Wm(-2). In an alternative approach, the radiative flux perturbation due to anthropogenic aerosols can be broken down into a component over the cloud-free portion of the globe (approximately the aerosol direct effect) and a component over the cloudy portion of the globe (approximately the aerosol indirect effect). An estimate obtained by scaling these simulated clear- and cloudy-sky forcings with estimates of anthropogenic tau(a) and satellite-retrieved N-d-tau(a) regression slopes, respectively, yields a global, annual-mean aerosol direct effect estimate of -0.4 +/- 0.2 Wm(-2) and a cloudy-sky (aerosol indirect effect) estimate of -0.7 +/- 0.5 Wm(-2), with a total estimate of -1.2 +/- 0.4 Wm(-2).

DOI： 10.5194/acp-9-8697-2009

Language：English   Publishing type：Research paper (scientific journal)  

Mineral dust is usually transported long distances in the lower troposphere. There are examples of Asian dust being transported across the Pacific Ocean(1-7), and traces of Asian dust have also been found in ice and snow cores in Greenland(8) and the French Alps(9). Here, we use measurements from the Cloud-Aerosol Lidar with Orthogonal Polarization(10), an air parcel trajectory model and a three-dimensional aerosol transport model to map the transport of dust clouds generated during a storm in China's Taklimakan Desert during May 2007. We show that the dust-veiled clouds were lofted to the upper troposphere around 8-10 km above the Earth's surface and transported more than one full circuit around the globe in about 13 days. When the dust reached the northwestern Pacific Ocean for the second time, the subsidence of a large-scale high-pressure system caused it to descend into the lower troposphere; some of the dust was then deposited over the ocean. Our analysis also indicates that the dust particles may have acted as ice nuclei in these high-altitude clouds, leading to the formation of cirrus clouds. We suggest that Asian dust can influence the global radiation budget by stimulating cirrus cloud formation and marine ecosystems by supplying nutrients to the open ocean.

DOI： 10.1038/NGEO583

Language：Japanese   Publishing type：Research paper (scientific journal)  

Development of forecasting system for atmospheric aerosols

Language：English   Publishing type：Research paper (scientific journal)  

Detailed 3-D structures of Trans-Pacific Asian dust transport occurring during 5-15 May 2007 were investigated using the NASA/CALIOP vertical-resolved measurements and a three-dimensional aerosol model (SPRINTARS). Both CALIOP and SPRINTARS dust extinctions showed a good agreement along the way of the transport from the dust source regions across North Pacific into North America. A vertically two-layered dust distribution was observed over the northeastern Pacific and North America. The lower dust layer originated from a dust storm generated in the Gobi Desert on 5 May. It was transported at an altitude of around 4 km MSL and has mixed with Asian anthropogenic air pollutants during the course of transport. The upper dust layer mainly originated from a dust storm that occurred in the Taklimakan Desert 2-3 days after the Gobi dust storm generation. The upper dust cloud was transported in higher altitudes above the major clouds layer during the Trans-Pacific transport. It therefore has remained unmixed with the Asian air pollutants and almost unaffected by wet removal. The decay of its concentration level was small (only one-half after its long-distance transport crossing the Pacific). Our dust budget analysis revealed that the Asian dust flux passing through the longitude plane of 140 degrees E was 2.1 Tg, and one third of that arrived North America. The cases analyzed in this study revealed that, while the Gobi Desert is an important source that can contribute to the long-range dust transport, the Taklimakan Desert appears to be another important source that can contribute to the dust transport occurring particularly at high altitudes.

DOI： 10.5194/acp-9-3137-2009

Language：English   Publishing type：Research paper (scientific journal)  

[1] The impact of aerosols on precipitation occurrence in warm clouds is assessed using a combination of multisensor satellite cloud and precipitation data sets and aerosol information from both satellite and a global transport model. Aerosols are found to suppress the formation of precipitation in polluted regions, evidenced by a trend toward higher liquid water path prior to the onset of light rainfall. Polluted clouds are also found to be more vertically developed than those in more pristine environments. Coupled with an apparent reduction in the size of the raindrops that subsequently form in these clouds, these findings indicate that pollution inhibits precipitation processes by redistributing water among a greater number of smaller cloud droplets. Evidence is also provided that sea-salt aerosols have the opposite effect on precipitation development. Maritime clouds that form in regions of enhanced sea-salt concentrations tend to precipitate more frequently, form larger raindrops, and be less vertically developed. This suggests that the nucleation of sea-salt particles may provide a source of embryonic raindrops in maritime clouds accelerating precipitation processes and ultimately reducing cloud lifetime. The net effect of aerosols on the onset of precipitation in any given region is, therefore, defined by the relative magnitudes of the competing effects of sulfate aerosols and sea-salt particles, the strengths of which depend strongly on both cloud liquid water path and the thermodynamic properties of the local environment. Copyright 2009 by the American Geophysical Union.

DOI： 10.1029/2008JD011273

Language：English   Publishing type：Research paper (scientific journal)  

In the subtropical oceans, nutrient concentrations are frequently below the detection limits of standard analytical methods. We applied a highly sensitive method to the surface water of the western and central Pacific between 42 degrees N and 40 degrees S and between 141 degrees E and 158 degrees W except in the equatorial zone, and detected overall depletion of nitrate + nitrite and an excess of SRP. However, a remarkable exception was found: an almost complete exhaustion of SRP (< 10 nM) existed at a horizontal scale of > 2000 km in the western subtropical North Pacific in both summer and winter. The SRP exhaustion was a consequence of an elevated dinitrogen fixation, which occurred in areas with high dust deposition from the Asian continent that likely enhanced SRP consumption. A coupling among nutrient dynamics, dinitrogen fixation and dust deposition produces the extremely low P availability spanning a large area, which appears to be unique to the western North Pacific. Citation: Hashihama, F., K. Furuya, S. Kitajima, S. Takeda, T. Takemura, and J. Kanda (2009), Macro-scale exhaustion of surface phosphate by dinitrogen fixation in the western North Pacific, Geophys. Res. Lett., 36, L03610, doi: 10.1029/2008GL036866.

DOI： 10.1029/2008GL036866

Language：English   Publishing type：Research paper (scientific journal)  

This study examined the vertical cloud structure over the tropical western Pacific Ocean using 95-GHz radar and lidar data observed from September to December 2001 during the MR01-K05 cruise of the research vessel Mirai. The cloud vertical structure was homogeneous between 6 and 10 km, and the maximum cloud occurrence was 20&#37; and located at 12 km. The mean precipitation occurrence was 11.5&#37; at 1 km. The cloud fraction, radar reflectivity factor, and lidar backscattering coefficient were simulated along the Mirai cruise track using the output from the Center for Climate System Research, University of Tokyo
National Institute for Environmental Studies
and Frontier Research Center for Global Change (CCSR/NIES/FRCGC) general circulation model (GCM). The original output showed the maximum cloud fraction at 15 km
however, after considering attenuation and the minimum sensitivity of the radar, the maximum shifted to 12 km. The model overestimated the cloud fraction above 8 km, with the simulated fraction more than twice as large as the observed fraction. The model overpredicted the frequency of deep convection reaching the upper atmosphere above 12 km. Further, it overestimated precipitation frequency. Simulated radar reflectivity was underestimated throughout the entire altitude range, whereas simulated and observed lidar backscattering were in good agreement above 12 km with subgrid-scale treatment. The ice effective radius of 40 μm and ice water content were reasonable in thin clouds, but the radius was underestimated in other regions. The simulated liquid water content was overestimated. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2008JD009812

Language：English   Publishing type：Research paper (scientific journal)  

Using two-wavelength lidar with one-wavelength depolarization measurement installed on the research vessel Mirai, we retrieved vertical distributions of extinction coefficients of water-soluble, sea-salt, and dust particles at 532 nm. In the retrieval, the mode radii, standard deviations, and refractive indexes for each aerosol component are prescribed
the retrieval uncertainties due to spherical assumption in our dust model are estimated to be 30-50&#37;. The ship-based measurements were conducted in the western Pacific Ocean near Japan from 14 to 27 May 2001. For the analysis, we applied two-wavelength lidar algorithms to the three-channel lidar data, i.e., for signal strengths at 532 and 1064 nm and the total depolarization ratio at 532 nm. Water-soluble and sea-salt particles occurred below 1 km, whereas air masses dominated by water-soluble and dust particles were sometimes found above 1 km. We also investigated the correlation of sea-salt extinction coefficient with surface wind velocity for various altitudes. A positive correlation was found at low altitude, but no correlation was indicated at high altitude. We also compared the extinction coefficients of water-soluble and sea-salt particles directly under cloud bottom with those in clear-sky. Below clouds, the extinction coefficients of water-soluble and sea-salt particles were 1.6 and 1.4 times larger, respectively, than those in clear sky
this could be explained by hygroscopic growth using Hänel theory. Finally, we evaluated the global aerosol transport model SPRINTARS using the retrieved aerosol properties and measured lidar signals. The model underestimated sea salt and overestimated dust, although the general patterns agreed with the observed patterns. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JD009640

Language：English   Publishing type：Research paper (scientific journal)  

We simulated the interactions of aerosols with liquid clouds using an aerosol-coupled global cloud-system-resolving model with horizontal resolution of 7 km, and the results are compared with satellite observations of cloud and aerosols. The result shows detailed spatial structures of cloud droplet effective radii (CDR) realistically simulated especially over tropics. The global correlation statistics of liquid water path (LWP) with aerosol index (AI) are investigated for different cloud types to reveal that the LWP slightly decreases with increasing AI, closely resembling satellite-observed features. The CDRs for different cloud types are also shown to decrease with increasing AI, and the sensitivities are found to be relatively similar among cloud types although of discrepancy in absolute values between the model and satellite observation. The model also simulates vertical growth patterns of liquid droplets and their interactions with aerosols in a manner similar to satellite observations.

DOI： 10.1029/2008GL035449

Language：English   Publishing type：Research paper (scientific journal)  

We examine the response of Arctic gas and aerosol concentrations to perturbations in pollutant emissions from Europe. East and South Asia, and North America using results from a coordinated model intercomparison. These sensitivities to regional emissions (mixing ratio change per unit emission) vary widely across models and species. Intermodel differences are systematic, however, so that the relative importance of different regions is robust. North America contributes the most to Arctic ozone pollution. For aerosols and CO, European emissions dominate at the Arctic surface but East Asian emissions become progressively more important with altitude, and arc dominant in the upper troposphere. Sensitivities show strong seasonality: surface sensitivities typically maximize during boreal winter for European and during spring for East Asian and North American emissions. Mid-tropospheric sensitivities, however, nearly always maximize during spring or summer for all regions. Deposition of black carbon (BC) onto Greenland is most sensitive to North American emissions. North America and Europe each contribute similar to 40&#37; of total BC deposition to Greenland, with similar to 20&#37; from East Asia. Elsewhere in the Arctic, both sensitivity and total BC deposition are dominated by European emissions. Model diversity for aerosols is especially large, resulting primarily from differences in aerosol physical and chemical processing, (including removal). Comparison of modeled aerosol concentrations with observations indicates problems in the models, and perhaps, interpretation of the measurements. For gas phase pollutants such as CO and O-3, which are relatively well-simulated, the processes contributing most to uncertainties depend on the source region and altitude examined. Uncertainties in the Arctic surface CO response to emissions perturbations are dominated by emissions for East Asian sources, while uncertainties in transport, emissions. and oxidation are comparable for European and North American sources. At higher levels. model-to-model variations in transport and oxidation are most important. Differences in photochemistry appear to play the largest role in the intermodel variations in Arctic ozone sensitivity, though transport also contributes substantially in the mid-troposphere.

DOI： 10.5194/acp-8-5353-2008

Language：English   Publishing type：Research paper (scientific journal)  

A bin-based microphysics scheme for cloud is implemented into a three-dimensional nonhydrostatic model and off-line coupled with a global aerosol transport model to reproduce realistic and inhomogeneous condensation nuclei (CN) fields. This coupling makes it possible to calculate cloud microphysical properties over a larger area under more realistic environmental conditions. Using the model, nested grid simulations are performed for two precipitation events associated with transitional synoptic-scale forcing during the spring over an area of the East China Sea. The nested grid simulations reproduce the general features of the horizontal distributions of variables such as effective droplet radius derived from satellite data retrieval. Comparison of the relationships among simulated cloud variables with those among satellite-derived variables reveals that the implementation of an inhomogeneous CN field results in a more accurate simulation of the distribution of cloud microphysical properties. Sensitivity tests with respect to CN concentration show that the simulated area and amount of precipitation are slightly affected by the CN concentration. Comparative simulations using bin-based and bulk microphysical schemes indicate that the difference in cloud microphysics has little effect on precipitation except over the areas of elevated pollution (i.e., elevated CN). Comparison with previous reports indicates that the precipitation response to aerosols is dependent on the environmental conditions and the type of the cloud system. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JD009774

Language：English   Publishing type：Research paper (scientific journal)  

We investigated the effects of man-made air pollutants on the climate of East Asia, focusing on eastern China where anthropogenic aerosol concentrations are rapidly increasing. The increasing emission of anthropogenic aerosols causes serious air pollution episodes and various effects on the climate in this region. It is therefore necessary to quantify the contribution of aerosols to the change in the radiation budget and the cloud field. Our purpose of this study is to evaluate the sensitivity of anthropogenic aerosols and other anthropogenic factors such as greenhouse gas (GHG) upon the radiative forcing. Then an aerosol transport model coupled to a general circulation model and an ocean mixed-layer model was used to investigate the relationships among the anthropogenic aerosol forcing, GHG forcing, surface radiation budget, and cloud field. Our simulation results showed that copious anthropogenic aerosol loading causes significant decrease in the surface downward shortwave radiation flux (SDSWRF), which indicates that a direct effect of aerosols has the greatest influence on the surface radiation. It is found from our model simulations that low-level clouds increase but convective clouds decrease due to reduced convective activity caused by surface cooling when anthropogenic aerosol increases, and GHG increase has an insignificant effect on SDSWRF but a significant effect on the cloud field. In other word model simulations suggested that the aerosol forcing mainly causes a reduction of SDSWRF, whereas the change in the cloud field is influenced both anthropogenic aerosol and GHG effects. Thus this work demonstrated with sensitivity experiments the importance of aerosols to cause significant climate effects in the East Asian region, though further study is needed because our study is based on results from one specific model and limited data analysis. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JD009325

Language：English   Publishing type：Research paper (scientific journal)  

A global three-dimensional aerosol transport-radiation model, coupled to an atmospheric general circulation model (AGCM), has been extended to improve the model process for organic aerosols, particularly secondary organic aerosols (SOA), and to estimate SOA contributions to direct and indirect radiative effects. Because the SOA formation process is complicated and unknown, the results in different model simulations include large differences. In this work, we simulate SOA production assuming various parameterizations of (1) primary organic aerosols (POA) mass concentrations, (2) oxidant species concentrations, and (3) volatile organic compound (VOC) concentrations in the SOA formation through gas-to-particle conversion governed by equilibrium partitioning of monoterpene oxidation products. Comparisons of results from observations, other models, and our simulations with/without the SOA partitioning theory lead to some findings of the influence of SOA on the radiation and cloud fields. First, the SOA number concentrations control cloud droplet effective radii near water cloud tops in the tropics and can affect the estimation of the aerosol indirect radiative effect. Second, SOA simulation results strongly depend on POA concentrations and emission data, so that disregarding this dependence may lead to a significant underestimation of the aerosol radiative effect because most of other studies assume that the SOA production level in the preindustrial era is same as in the current level. The global annual mean production of SOA formed from monoterpene is evaluated in this study as 6.74 Tg a&lt
sup&gt
-1&lt
/sup&gt
, and the global annual mean radiative forcings of the direct and indirect effects by SOA from monoterpene are calculated to be -0.01 and -0.19 W m&lt
sup&gt
-2&lt
/sup&gt
, respectively. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2007JD009019

Language：English   Publishing type：Research paper (scientific journal)  

This article introduces an international regional experiment, East Asian Regional Experiment 2005 (EAREX 2005), carried out in March-April 2005 in the east Asian region, as one of the first phase regional experiments under the UNEP Atmospheric Brown Cloud (ABC) project, and discusses some outstanding features of aerosol characteristics and its direct radiative forcing in the east Asian region, with some comparison with the results obtained in another ABC early phase regional experiment, ABC Maldives Monsoon Experiment (APMEX) conducted in the south Asian region. Time series of aerosol optical thickness (AOT), single scattering albedo (SSA), aerosol extinction cross section profile and CO concentration shows that air pollutants and mineral dust were transported every 5 to 7 days in the EAREX region to produce SSA values at wavelength of 700 nm from 0.86 to 0.96 and large clear-sky shortwave forcing efficiency at 500 nm from 60 W m&lt
sup&gt
-2&lt
/sup&gt
to go W m&lt
sup&gt
-2&lt
/sup&gt
, though there are some unexplained inconsistencies depending on the evaluation method. The simulated whole-sky total forcing in the EAREX region is -1 to - 2 W m&lt
sup&gt
-2&lt
/sup&gt
at TOA and -2 to -10 W m&lt
sup&gt
-2&lt
/sup&gt
at surface in March 2005 which is smaller in magnitude than in the APMEX region, mainly because of large cloud fraction in this region (0.70 at Gosan versus 0.51 at Hanimadhoo in the ISCCP total cloud fraction). We suggest there may be an underestimation of the forcing due to overestimation of the simulated cloudiness and aerosol scale height. On the other hand, the possible error in the simulated surface albedo may cause an overestimation of the magnitude of the forcing over the land area. We also propose simple formulae for shortwave radiative forcing to understand the role of aerosol parameters and surface condition to determine the aerosol forcing. Such simple formulae are useful to check the consistency among the observed quantities. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2007JD009009

Language：English   Publishing type：Research paper (scientific journal)  

The Atmospheric Brown Cloud-East Asia Regional Experiment (ABC-EAREX) was conducted under the UNEP/ABC-Asia project to intercompare the aerosol and gas measurements in springtime from various instruments from late February to April 2005 at the Gosan Supersite on Jeju Island, Korea. Satellite instruments such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Ozone Monitoring Instrument (OMI) provide a large-scale regional view of the aerosol during the ABC-EAREX period. This study shows the temporal and spatial distribution of four major aerosol types (dust, carbonaceous, sea salt and sulfate) retrieved by MODIS-OMI Algorithm and Four-Channel Algorithm utilizing data from MODIS and OMI over east Asia during the ABC-EAREX campaign. Results from two different retrieval show that a complexity of aerosol types and sources exist over east Asia: Some aerosols are emitted while others are transported. Nevertheless, the results show reasonable consistency in the distribution according to aerosol type. The agreement of aerosol type classification for each aerosol type ranges from 32&#37; to 81&#37; depending on the type. These results were compared with the results from a three-dimensional aerosol transport radiation model, SPRINTARS. Dust type aerosol is usually found to be mixed with carbonaceous type aerosol. It implies that the dust type aerosol is loaded and transported with polluted air mass. The evidence that polluted air masses in the continent can be transported long distance is also captured
that is, sea salt type mixed with the sulfate aerosol is detected over a remote ocean. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JD008201

Language：English   Publishing type：Research paper (scientific journal)  

Aerosols affect the earth's climate by scattering and absorbing radiation, and by altering the cloud microphysics. Since the effects of aerosols are different from the type to the other, aerosol type classification from satellite remote sensing is challenging. In this study, types of aerosol are classified into dust, sea salt, smoke plume, and sulfate by using aerosol optical thickness (AOT) and Angstrom exponent (AE) of Moderate Resolution Imaging Spectroradiometer ( MODIS) and aerosol index ( AI) of Ozone Monitoring Instrument (OMI) data. The optical properties and types of aerosol are analyzed over the East Asia, one of the heavily polluted regions on the globe. AOTs significantly decrease from near-continent ocean to remote ocean in monthly climatology, and the maximum AOT is represented in June over the Northeast China, Korean Peninsula, and Japan. The distribution of AEs indicates that aerosols of anthropogenic as well as natural origin exist over both land and ocean in East Asia. The seasonal variation of AI is represented over the regions with latitude between 30 degrees N and 40 degrees N where the influence of Asian Dust is significant in dry season. Retrieved aerosol types by MODIS-OMI algorithm showed that the aerosols are considerably mixed, and represented seasonal variation over East Asia. The evidence of pollution transport is detected by aerosol classification, that is, the anthropogenic aerosol types are detected over ocean not only over land. Based on retrieved aerosol types, the frequency distributions of each aerosol type are analyzed in Beijing, Seoul, and Tokyo. Dust type aerosol is most frequently detected followed by mixtures of sea salt/sulfate at Beijing, whereas sea salt/sulfate mixture is most frequently detected at Seoul and Tokyo. The frequency distributions of aerosol types are similar for both in 2005 and 2006, while the distribution showed considerable seasonal variations.

Language：English   Publishing type：Research paper (scientific journal)  

The effects of unified aerosol sources on global aerosol fields simulated by different models are examined in this paper. We compare results from two AeroCom experiments, one with different (ExpA) and one with unified emissions, injection heights, and particle sizes at the source (ExpB). Surprisingly, harmonization of aerosol sources has only a small impact on the simulated inter-model diversity of the global aerosol burden, and consequently global optical properties, as the results are largely controlled by model-specific transport, removal, chemistry (leading to the formation of secondary aerosols) and parameterizations of aerosol microphysics (e.g., the split between deposition pathways) and to a lesser extent by the spatial and temporal distributions of the (precursor) emissions.
The burdens of black carbon and especially sea salt become more coherent in ExpB only, because the large ExpA diversities for these two species were caused by a few outliers. The experiment also showed that despite prescribing emission fluxes and size distributions, ambiguities in the implementation in individual models can lead to substantial differences.
These results indicate the need for a better understanding of aerosol life cycles at process level (including spatial dispersal and interaction with meteorological parameters) in order to obtain more reliable results from global aerosol simulations. This is particularly important as such model results are used to assess the consequences of specific air pollution abatement strategies.

DOI： 10.5194/acp-7-4489-2007

Language：English   Publishing type：Research paper (scientific journal)  

We observed the vertical distribution of clouds over the Pacific Ocean near Japan in May 2001 using lidar and a 95-GHz radar on the Research Vessel Mirai. Cloud analyses derived from synergy use of radar and lidar observations showed that there were two local maxima of cirrus cloud frequency of occurrence at 7 and 10.5 km and the drizzle frequency of occurrence was about the half compared with that of clouds below 4 km. The number of layers could be also measured using these schemes. Single, double, triple, and quadruple (or more) cloud layers had a 48, 23, 7, and 2&#37; probability of occurrence, respectively. The average number of cloud layers when clouds existed was 1.54. The vertical structure of clouds observed with the radar/lidar system was compared to clouds in the aerosol transport model SPRINTARS, which is based on the CCSR-NIES Atmospheric General Circulation Model. The cloud fraction, radar reflectivity factor, and lidar backscattering coefficient were simulated by the model and compared to those by the observations using height-time cross-sections where the radar sensitivity was taken into account. The overall pattern of cloud fraction was well reproduced, although the model underestimated (overestimated) mean cloud fraction below 8 km (above 8 km). Cloud microphysics in the model could also be validated through comparison of derived model radar and lidar signals in grid mean with observations. The model overestimated ice particle size above 10 km, and simulated particle sizes in water clouds of 10 μm were larger than observed. Copyright 2007 by the American Geophysical Union.

DOI： 10.1029/2006JD007628

Language：English   Publishing type：Research paper (scientific journal)  

Nine different global models with detailed aerosol modules have independently produced instantaneous direct radiative forcing due to anthropogenic aerosols. The anthropogenic impact is derived from the difference of two model simulations with prescribed aerosol emissions, one for present-day and one for pre-industrial conditions. The difference in the solar energy budget at the top of the atmosphere (ToA) yields a new harmonized estimate for the aerosol direct radiative forcing (RF) under all-sky conditions. On a global annual basis RF is -0.22 Wm(-2), ranging from +0.04 to -0.41 Wm(-2), with a standard deviation of +/- 0.16 Wm(-2). Anthropogenic nitrate and dust are not included in this estimate. No model shows a significant positive all-sky RF. The corresponding clear-sky RF is -0.68 Wm(-2). The cloud-sky RF was derived based on all-sky and clear-sky RF and modelled cloud cover. It was significantly different from zero and ranged between -0.16 and +0.34 Wm(-2). A sensitivity analysis shows that the total aerosol RF is influenced by considerable diversity in simulated residence times, mass extinction coefficients and most importantly forcing efficiencies (forcing per unit optical depth). The clear-sky forcing efficiency (forcing per unit optical depth) has diversity comparable to that for the all-sky/clear-sky forcing ratio. While the diversity in clear-sky forcing efficiency is impacted by factors such as aerosol absorption, size, and surface albedo, we can show that the all-sky/clear-sky forcing ratio is important because all-sky forcing estimates require proper representation of cloud fields and the correct relative altitude placement between absorbing aerosol and clouds. The analysis of the sulphate RF shows that long sulphate residence times are compensated by low mass extinction coefficients and vice versa. This is explained by more sulphate particle humidity growth and thus higher extinction in those models where short-lived sulphate is present at lower altitude and vice versa. Solar atmospheric forcing within the atmospheric column is estimated at +0.82 +/- 0.17 Wm(-2). The local annual average maxima of atmospheric forcing exceed +5 Wm(-2) confirming the regional character of aerosol impacts on climate. The annual average surface forcing is -1.02 +/- 0.23 Wm(-2). With the current uncertainties in the modelling of the radiative forcing due to the direct aerosol effect we show here that an estimate from one model is not sufficient but a combination of several model estimates is necessary to provide a mean and to explore the uncertainty.

DOI： 10.5194/acp-6-5225-2006

Language：English   Publishing type：Research paper (scientific journal)  

Modeled differences in predicted effects are increasingly used to help quantify the uncertainty of these effects. Here, we examine modeled differences in the aerosol indirect effect in a series of experiments that help to quantify how and why model-predicted aerosol indirect forcing varies between models. The experiments start with an experiment in which aerosol concentrations, the parameterization of droplet concentrations and the autoconversion scheme are all specified and end with an experiment that examines the predicted aerosol indirect forcing when only aerosol sources are specified. Although there are large differences in the predicted liquid water path among the models, the predicted aerosol first indirect effect for the first experiment is rather similar, about - 0.6 Wm(-2) to - 0.7 W m(-2). Changes to the autoconversion scheme can lead to large changes in the liquid water path of the models and to the response of the liquid water path to changes in aerosols. Adding an autoconversion scheme that depends on the droplet concentration caused a larger ( negative) change in net outgoing shortwave radiation compared to the 1st indirect effect, and the increase varied from only 22&#37; to more than a factor of three. The change in net shortwave forcing in the models due to varying the autoconversion scheme depends on the liquid water content of the clouds as well as their predicted droplet concentrations, and both increases and decreases in the net shortwave forcing can occur when autoconversion schemes are changed. The parameterization of cloud fraction within models is not sensitive to the aerosol concentration, and, therefore, the response of the modeled cloud fraction within the present models appears to be smaller than that which would be associated with model "noise". The prediction of aerosol concentrations, given a fixed set of sources, leads to some of the largest differences in the predicted aerosol indirect radiative forcing among the models, with values of cloud forcing ranging from - 0.3W m(-2) to - 1.4 W m(-2). Thus, this aspect of modeling requires significant improvement in order to improve the prediction of aerosol indirect effects.

DOI： 10.5194/acp-6-3391-2006

Language：English   Publishing type：Research paper (scientific journal)  

Simulation results of global aerosol models have been assembled in the framework of the AeroCom intercomparison exercise. In this paper, we analyze the life cycles of dust, sea salt, sulfate, black carbon and particulate organic matter as simulated by sixteen global aerosol models. The differences among the results (model diversities) for sources and sinks, burdens, particle sizes, water uptakes, and spatial dispersals have been established. These diversities have large consequences for the calculated radiative forcing and the aerosol concentrations at the surface. Processes and parameters are identified which deserve further research.
The AeroCom all-models-average emissions are dominated by the mass of sea salt (SS), followed by dust (DU), sulfate (SO4), particulate organic matter (POM), and finally black carbon (BC). Interactive parameterizations of the emissions and contrasting particles sizes of SS and DU lead generally to higher diversities of these species, and for total aerosol. The lower diversity of the emissions of the fine aerosols, BC, POM, and SO4, is due to the use of similar emission inventories, and does therefore not necessarily indicate a better understanding of their sources. The diversity of SO4-sources is mainly caused by the disagreement on depositional loss of precursor gases and on chemical production. The diversities of the emissions are passed on to the burdens, but the latter are also strongly affected by the model-specific treatments of transport and aerosol processes. The burdens of dry masses decrease from largest to smallest: DU, SS, SO4, POM, and BC.
The all-models-average residence time is shortest for SS with about half a day, followed by SO4 and DU with four days, and POM and BC with six and seven days, respectively. The wet deposition rate is controlled by the solubility and increases from DU, BC, POM to SO4 and SS. It is the dominant sink for SO4, BC, and POM, and contributes about one third to the total removal of SS and DU species. For SS and DU we find high diversities for the removal rate coefficients and deposition pathways. Models do neither agree on the split between wet and dry deposition, nor on that between sedimentation and other dry deposition processes. We diagnose an extremely high diversity for the uptake of ambient water vapor that influences the particle size and thus the sink rate coefficients. Furthermore, we find little agreement among the model results for the partitioning of wet removal into scavenging by convective and stratiform rain.
Large differences exist for aerosol dispersal both in the vertical and in the horizontal direction. In some models, a minimum of total aerosol concentration is simulated at the surface. Aerosol dispersal is most pronounced for SO4 and BC and lowest for SS. Diversities are higher for meridional than for vertical dispersal, they are similar for the individual species and highest for SS and DU. For these two components we do not find a correlation between vertical and meridional aerosol dispersal. In addition the degree of dispersals of SS and DU is not related to their residence times. SO4, BC, and POM, however, show increased meridional dispersal in models with larger vertical dispersal, and dispersal is larger for longer simulated residence times.

DOI： 10.5194/acp-6-1777-2006

Language：English   Publishing type：Research paper (scientific journal)  

The AeroCom exercise diagnoses multicomponent aerosol modules in global modeling. In an initial assessment simulated global distributions for mass and mid-visible aerosol optical thickness (aot) were compared among 20 different modules. Model diversity was also explored in the context of previous comparisons. For the component combined aot general agreement has improved for the annual global mean. At 0.11 to 0.14, simulated aot values are at the lower end of global averages suggested by remote sensing from ground (AERONET ca. 0.135) and space ( satellite composite ca. 0.15). More detailed comparisons, however, reveal that larger differences in regional distribution and significant differences in compositional mixture remain. Of particular concern are large model diversities for contributions by dust and carbonaceous aerosol, because they lead to significant uncertainty in aerosol absorption (aab). Since aot and aab, both, influence the aerosol impact on the radiative energy-balance, the aerosol (direct) forcing uncertainty in modeling is larger than differences in aot might suggest. New diagnostic approaches are proposed to trace model differences in terms of aerosol processing and transport: These include the prescription of common input (e.g. amount, size and injection of aerosol component emissions) and the use of observational capabilities from ground (e.g. measurements networks) or space (e.g. correlations between aerosol and clouds).

DOI： 10.5194/acp-6-1815-2006

Language：English   Publishing type：Research paper (scientific journal)  

Simulations using a climate model are used to investigate the possible impact of increasing emissions of carbonaceous aerosols on near-surface temperature in the mid-20th century. The annual global mean near-surface temperature change from the mid-20th century onward is reasonably described by a model that is forced by changes in most of the known climate forcing agents including an increase in carbonaceous aerosols, though it can also be well reproduced without increases in carbonaceous aerosols. However, if we consider spatio-temporal structure of the changes in the near-surface temperature, an increase in carbonaceous aerosols is definitely required for the model to represent changes in the near-surface temperature in the mid-century, in particular, cooling trends in the tropical and subtropical continents. The significance of an increase in carbonaceous aerosols as an indispensable contributor to mid-20th century temperature changes is confirmed with the use of an optimal fingerprinting methodology.

DOI： 10.1029/2005GL024887

Language：English   Publishing type：Research paper (scientific journal)  

Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (tau), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model CTM) simulations. The multi-spectral MODIS measures global distributions of aerosol optical depth (tau) on a daily scale, with a high accuracy of +/- 0.03 +/- 0.05 tau over ocean. The annual average tau is about 0.14 over global ocean, of which about 21&#37; +/- 7&#37; is contributed by human activities, as estimated by MODIS fine-mode fraction. The multi-angle MISR derives an annual average AOD of 0.23 over global land with an uncertainty of similar to 20&#37; or +/- 0.05. These high-accuracy aerosol products and broadband flux measurements from CERES make it feasible to obtain observational constraints for the aerosol direct effect, especially over global the ocean. A number of measurement-based approaches estimate the clear-sky DRE ( on solar radiation) at the top-of-atmosphere (TOA) to be about - 5.5 +/- 0.2 W m(-2) ( median +/- standard error from various methods) over the global ocean. Accounting for thin cirrus contamination of the satellite derived aerosol field will reduce the TOA DRE to -5.0 W m(-2). Because of a lack of measurements of aerosol absorption and difficulty in characterizing land surface reflection, estimates of DRE over land and at the ocean surface are currently realized through a combination of satellite retrievals, surface measurements, and model simulations, and are less constrained. Over the oceans the surface DRE is estimated to be - 8.8 +/- 0.7W m(-2). Over land, an integration of satellite retrievals and model simulations derives a DRE of - 4.9 +/- 0.7W m(-2) and - 11.8 +/- 1.9W m(-2) at the TOA and surface, respectively. CTM simulations derive a wide range of DRE estimates that on average are smaller than the measurement-based DRE by about 30 - 40&#37;, even after accounting for thin cirrus and cloud contamination.
A number of issues remain. Current estimates of the aerosol direct effect over land are poorly constrained. Uncertainties of DRE estimates are also larger on regional scales than on a global scale and large discrepancies exist between different approaches. The characterization of aerosol absorption and vertical distribution remains challenging. The aerosol direct effect in the thermal infrared range and in cloudy conditions remains relatively unexplored and quite uncertain, because of a lack of global systematic aerosol vertical profile measurements. A coordinated research strategy needs to be developed for integration and assimilation of satellite measurements into models to constrain model simulations. Enhanced measurement capabilities in the next few years and high-level scientific cooperation will further advance our knowledge.

DOI： 10.5194/acp-6-613-2006

Language：English   Publishing type：Research paper (scientific journal)  

The Arabian Sea region (4 degrees N-20 degrees N to 50 degrees E-78 degrees E) has a unique weather pattern on account of the Indian monsoon and the associated winds that reverse direction seasonally. The aerosol data, collected using ship-borne and island platforms (for 8 years from 1995 to 2002) along with MODIS (onboard TERRA satellite) data (from 2000 to 2003) have been used to evolve a comprehensive characterisation of the spatial and temporal variation in the physical, chemical, and radiative properties of aerosols over the Arabian Sea. The aerosol optical depth (AOD) was found to increase with latitude between the equator and 12 degrees N. Over the northern Arabian Sea (regions lying north of 12 degrees N), AODs do not show significant latitudinal variations; the average aerosol optical depth for this region was 0.29 +/- 0.12 during winter monsoon season (WMS; November to March) and 0.47 +/- 0.14 during summer monsoon season (SMS; April/May to September). The corresponding Angstrom exponents were 0.7 +/- 0.12 and 0.3 +/- 0.08, respectively. The low values of the exponent during SMS indicate the dominance of large aerosols (mainly dust particles >1 mu m). The latitudinal gradient in AOD in the southern Arabian Sea is larger during SMS compared to WMS.
The size distribution of aerosols shows two well-defined modes, one in the accumulation size regime and the other in the coarse size regime. During WMS, a third mode (nucleation) also appears in the sub micron range below similar to 0.1 mu m. The single scattering albedo does not show significant seasonal variations (remains within similar to 0.93 to 0.98 through out the year). During WMS (SMS), top of the atmosphere diurnally averaged aerosol forcing remains around -6.1 (-14.3) W m(-2) over the northern Arabian Sea up to around 12 degrees N and decreases southwards till it attains a value of -3.8 (-3.4) W m(-2) at the equator. The surface forcing remains around -16.2 (-15.2) W m(-2) over the northern Arabian Sea up to 12 degrees N and decreases southwards to a value of -5.5 (-3.5) W m(-2) at the equator. Over the north Arabian Sea, instantaneous forcing (flux change) at the surface can be as high as -50 W m(-2). The instantaneous forcing decreases with latitude in the southern Arabian Sea at a rate of similar to 3 W m(-2) deg(-1).

DOI： 10.1007/s00703-004-0097-4

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Cloud microphysical properties derived from satellite data during December 2:000 and April 2001, Asian Atmospheric Particulate Environment Change Studies (APEX) Intensive Observational Period (IOP), are compared with ground and aircraft measurements. The target clouds are marine stratus and stratocumulus. They appeared over the Amami-Oshima Island, and off the south coast of Kyushu island. The principal goals of the comparison are to understand the characteristics of data obtained from each observing platform, and investigate the potentiality of synergistic use of multi platform data. The liquid water paths obtained from satellite (MODIS) observation by using the GLI cloud retrieval algorithm were compared with the ground-based measurements (microwave radiometer). The correlation coefficient and the root mean square error between ground and satellite liquid water path was 0.87 and 61.9 g/m(2). The satellite-retrieved cloud effective radius agreed with those from the aircraft measurements (FSSP) around the top of the cloud.

DOI： 10.2151/jmsj.83.1085

Language：English   Publishing type：Research paper (scientific journal)  

This document outlines a practical strategy for achieving an observationally based quantification of direct climate forcing by anthropogenic aerosols. The strategy involves a four-step program for shifting the current assumption-laden estimates to an increasingly empirical basis using satellite observations coordinated with suborbital remote and in situ measurements and with chemical transport models. Conceptually, the problem is framed as a need for complete global mapping of four parameters: clear-sky aerosol optical depth 8, radiative efficiency per unit optical depth E, fine-mode fraction of optical depth f(f) and the anthropogenic fraction of the fine a(f). The first three parameters can be retrieved from satellites, but correlative, suborbital measurements are required for quantifying the aerosol properties that control E, for validating the retrieval of f(f), and for partitioning fine-mode delta between natural and anthropogeniccomponents. The satellite focus is on the "A-Train," a constellation of six spacecraft that will fly in formation from about 2005 to 2008. Key satellite instruments for this report are the Moderate Resolution Imaging Spectroradiometer (MODIS) and Clouds and the Earth's Radiant Energy System (CERES) radiometers on Aqua, the Ozone Monitoring, Instrument (OMI) radiometer on Aura, the Polarization and Directionality of Earth's Reflectances (POLDER) polarimeter on the Polarization and Anistropy of Reflectances for Atmospheric Sciences Coupled with Observations from a Lidar (PARASOL), and the Cloud and Aerosol Lider with Orthogonal Polarization (CALIOP) lidar on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). This strategy is offered as an framework-subject to improvement over time-for scientists around the world to participate in the A-Train opportunity. It is a specific implementation of the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) program, presented earlier in this journal, which identified the integration of diverse data as the central challenge to progress in quantifying global-scale aerosol effects. By designing a strategy around this need for integration, we develop recommendations for both satellite data interpretation and correlative suborbital activities that represent, in many respects, departures from current practice.

DOI： 10.1175/BAMS-86-12-1795

Language：English   Publishing type：Research paper (scientific journal)  

Dust layers in the free troposphere were observed with the lidars in Suwon, Gosan, and Tsukuba in March 7-9, 2005. The observed dust distributions were compared with the results of the regional and global dust transport models (CFORS, NRL NAAPS, and SPRINTARS). The results with the global models reproduced the dust layer qualitatively, but the regional model did not. This suggests the source of the dust layers is located outside of the modeled region of the regional model that includes Taklimakan Desert and Gobi Desert. The global models showed the plumes were from the Sahara Desert, and the both models showed there was no major dust emission in Taklimakan and Gobi Deserts during the observation period. The trajectory analysis using NOAA HYSPLIT showed that the dust originated in the Sahara Desert 5-10 days before.

DOI： 10.2151/sola.2005-032

Language：English   Publishing type：Research paper (scientific journal)  

Satellite instruments do not measure the aerosol chemical composition needed to discriminate anthropogenic from natural aerosol components. However the ability of new satellite instruments to distinguish fine (submicron) from coarse (supermicron) aerosols over the oceans, serves as a signature of the anthropogenic component and can be used to estimate the fraction of anthropogenic aerosols with an uncertainty of +/-30&#37;. Application to two years of global MODIS data shows that 21 +/- 7&#37; of the aerosol optical thickness over the oceans has an anthropogenic origin. We found that three chemical transport models, used for global estimates of the aerosol forcing of climate, calculate a global average anthropogenic optical thickness over the ocean between 0.030 and 0.036, in line with the present MODIS assessment of 0.033. This increases our confidence in model assessments of the aerosol direct forcing of climate. The MODIS estimated aerosol forcing over cloud free oceans is therefore -1.4 +/- 0.4 W/m(2).

DOI： 10.1029/2005GL023125

Language：English   Publishing type：Research paper (scientific journal)  

[1] The transport and optical thickness of tropospheric aerosols ( dust, sulfate, carbonaceous aerosols, and sea salt) during the ACE-Asia intensive observation period ( spring 2001) were simulated using a CFORS chemical transport model coupled with a regional meteorological model. Simulated aerosol fields were examined intensively with surface monitoring stations (PM102, sulfate, and total carbonaceous aerosol), Mie Lidar, and satellite observation data. It was shown that CFORS aerosol fields agree with observations and reproduced many observed characteristics including the several high concentration levels associated with the continental outflow, aerosol vertical profiles and strong correlation between dust and sulfate transports. We found the presence of the latitudinal gradient of aerosol concentrations from these comparisons. The two-month ( March and April) averaged aerosol concentration and AOT fields show this latitudinal gradient more clearly, and indicated that the main dust field is located between 30 N and 45 N, while sulfate and carbonaceous field are mainly dominant from their main sources in central China and Southeast Asia to northern Japan ( between 25 N and 45 N). Analyses of aerosol horizontal fluxes were also performed. We found that these distributions are closely related to characteristics of wind field of springtime and that each aerosol has the following transport route; the main dust flow is eastward along the 45 N parallel and is located in the free atmosphere; sulfate and carbonaceous aerosols within the boundary layer has a clockwise and divergent flow pattern over central China, which produce the strong outflow associated with anthropogenic emissions at northern latitudes and constrain the continental outflow at the southern latitude; and carbonaceous aerosols at the upper level ( 2 - 6 km) have another transport pathway that is along about 30 N from Thailand and Laos. Regional budgets of tropospheric aerosols showed that total emissions were 105 Tg for dust, 8.3 Tg-SO for sulfur (73&#37; from human activities and 27&#37; from volcanic activities), and 3.07 Tg for carbonaceous aerosols. Dry deposition, gravitational settling, and northward outflow of dust accounted for 33&#37;, 27&#37;, and 14&#37; of total emissions, respectively. Wet deposition, eastward outflow, and dry deposition of sulfur accounted for 33&#37;, 27&#37;, and 21&#37;, respectively. Regarding carbonaceous aerosols, the outflow to the east has the highest fraction (49&#37;), followed by dry deposition (16&#37;) and the outflow to the north ( 14&#37;).

DOI： 10.1029/2003JD003997

Language：Japanese  

Interannual Variation of 'Kosa' Simulated by a Regional-Scale Dust Transport Model.

Language：English   Publishing type：Research paper (scientific journal)  

Dust events have been observed in Japan with high frequency since 2000. On the other hand, the frequency of dust storms is said to have decreased in the desert regions of China since about the middle of the 1970s. This study simulates dust storms and transportation of mineral dust aerosols in the east Asia region from 1981 to 2001 using an aerosol transport model, Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS), implemented in the Center for Climate System Research/National Institute for Environmental Studies atmospheric global circulation model, in order to investigate the main factors that control a dust event and its long-term variation. The model was forced to simulate a real atmospheric condition by a nudging technique using European Centre for Medium-Range Weather Forecasts reanalysis data on wind velocities, temperature, specific humidity, soil wetness, and snow depth. From a comparison between the long-term change in the dust emission and model parameters, it is found that the wind speed near the surface level had a significant influence on the dust emission, and snow is also an important factor in the early spring dust emission. The simulated results suggested that dust emissions from northeast China have a great impact on dust mass concentration in downwind regions, such as the cities of northeastern China, Korea, and Japan. When the frequency of dust events was high in Japan, a low-pressure system tended to develop over the northeast China region that caused strong winds. From 2000 to 2001 the simulated dust emission flux decreased in the Taklimakan desert and the northwestern part of China, while it increased in the Gobi desert and the northeastern part of China. Consequently, dust particles seem to be transported more from the latter region by prevailing westerlies in the springtime to downwind areas as actually observed. In spite of the similarity, however, there is still a large disagreement between observed and simulated dust frequencies and concentrations. A more realistic land surface and uplift mechanism of dust particles should be modeled to improve the model simulation. Desertification of the northeastern China region may be another reason for this disagreement.

DOI： 10.1029/2003JD004270

Language：English   Publishing type：Research paper (scientific journal)  

The regional-scale aerosol transport model Chemical Weather Forecasting System (CFORS) is used for analysis of large-scale dust phenomena during the Asian Pacific Regional Characterization Experiment (ACE-Asia) intensive observation. Dust modeling results are examined with the surface weather reports, satellite-derived dust index (Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI)), Mie-scattering lidar observation, and surface aerosol observations. The CFORS dust results are shown to accurately reproduce many of the important observed features. Model analysis shows that the simulated dust vertical loading correlates well with TOMS AI and that the dust loading is transported with the meandering of the synoptic-scale temperature field at the 500-hPa level. Quantitative examination of aerosol optical depth shows that model predictions are within 20&#37; difference of the lidar observations for the major dust episodes. The structure of the ACE-Asia Perfect Dust Storm, which occurred in early April, is clarified with the help of the CFORS model analysis. This storm consisted of two boundary layer components and one elevated dust (>6-km height) feature (resulting from the movement of two large low-pressure systems). Time variation of the CFORS dust fields shows the correct onset timing of the elevated dust for each observation site, but the model results tend to overpredict dust concentrations at lower latitude sites. The horizontal transport flux at 130degreesE longitude is examined, and the overall dust transport flux at 130degreesE during March-April is evaluated to be 55 Tg.

DOI： 10.1029/2003JD004222

Language：English   Publishing type：Research paper (scientific journal)  

[1] Aerosol optical properties (aerosol optical thickness, Angstrom exponent, size distribution, and single scattering albedo) over east Asia were examined using long-term measurements of sky radiation at Mandalgovi, Dunhuang, Yinchuan, and Sri-Samrong sites of the Skyradiometer Network (SKYNET). Also included were sky radiation measurements at Anmyon, Gosan in Korea, and Amami-Oshima in Japan during April for examining optical properties of Asian dust. Results show that the seasonal average of aerosol optical thickness (AOT) generally exhibits a maximum in spring and a minimum in autumn over east Asia. At Sri-Samrong and Yinchuan, relatively distinct seasonal cycles are noted, in comparison to the arid desert regions of Dunhuang and Mandalgovi. In general, aerosol size distributions are characterized by a bimodal pattern, with a fine mode around 0.2 mum and a coarse mode around 2-5 mum. Similar to AOT and a, volume spectra are also much dependent on geographical location and season. Dunhuang mostly shows coarse mode particles in all seasons, while Mandalgovi and Sri-Samrong show large seasonal variations in the total volume of fine mode particles. The single scattering albedos of dust particles over east Asia are around 0.9 at 0.5 mum, which are larger than the previously known values of 0.63 - 0.89 but similar to those found in the Aerosol Robotic Network (AERONET) analysis. It is noted that the optical properties of Asian dust around Korea and Japan are quite similar to those found in dust source regions such as Dunhuang and Mandalgovi. However, the single scattering albedo appears to be smaller than those observed in Dunhuang and Mandalgovi. Furthermore, single scattering albedo tends to become smaller during the dust outbreak period. Considering that aerosols in Korean and Japanese areas are much influenced by anthropogenic aerosols emitted in China particularly under the westerly conditions, the mixing processes between different aerosol species may be the cause of the different optical properties of Asian dust.

DOI： 10.1029/2003JD003387

Language：English   Publishing type：Research paper (scientific journal)  

The indirect effect of aerosols was simulated by a GCM for nonconvective water clouds and was compared with remote sensing results from the Advanced Very High Resolution Radiometer (AVHRR) satellite-borne sensor for January, April, July, and October of 1990.
The simulated global distribution of cloud droplet radius showed a land-sea contrast and a characteristic feature along the coastal region similar to the AVHRR results, although cloud droplet radii from GCM calculations and AVHRR retrievals were different over tropical marine regions due to a lack of calculation of cloud-aerosol interaction for convective clouds in the present model and also due to a possible error in the satellite retrieval caused by cirrus and broken cloud contamination. The simulated dependence of the cloud properties on the column aerosol particle number was also consistent with the statistics obtained by the AVHRR remote sensing when a parameterization with the aerosol lifetime effect was incorporated in the simulation. The global average of the simulated liquid water path based on the parameterization with the aerosol lifetime effect showed an insignificant dependence on the aerosol particle number as a result of a global balance of the lifetime effect and the wash-out effect. This dependence was contrary to the results of simulations based on the Sundqvist's parameterization without aerosol lifetime effect; that is, the simulated cloud liquid water path showed a decreasing tendency with the aerosol particle number reflecting only the wash-out effect.

DOI： 10.1175/1520-0469(2004)061<0179:ASOTAE>2.0.CO;2

Language：English   Publishing type：Research paper (scientific journal)  

Radiative forcings of aerosols and clouds in the East China Sea region are studied using data from surface radiation measurements, satellite remote sensing, and model simulation conducted in April 2001 as a study of Asian Atmospheric Particle Environmental Change Studies ( APEX) cooperating with International Global Atmospheric Chemistry (IGAC)/ACE-Asia project. The monthly mean whole sky radiative forcing of the aerosol direct effect is derived from various methods as -5 to -8 W/m(2) at the top of atmosphere (TOA) and -10 to -23 W/m(2) at Earth's surface of Gosan (33.28N, 127.17E) and Amami-Oshima (28.15N, 129.30E) sites, though there is a large regional difference caused by changes in the aerosol optical thickness and single scattering albedo. The cloud forcing is estimated as -20 to -40 W/m(2), so that the aerosol direct forcing can be comparable to the cloud radiative forcing at surface. However, the estimate of the aerosol direct forcing thus obtained strongly depends on the estimation method of the aerosol properties, especially on the single scattering albedo, generating a method difference about 40&#37;. The radiative forcing of the aerosol indirect effect is roughly estimated from satellite method and SPRINTARS model as -1 to -3 W/m(2) at both TOA and surface.

DOI： 10.1029/2002JD003261

Language：English   Publishing type：Research paper (scientific journal)  

[1] New aerosol modules of global ( circulation and chemical transport) models are evaluated. These new modules distinguish among at least five aerosol components: sulfate, organic carbon, black carbon, sea salt, and dust. Monthly and regionally averaged predictions for aerosol mass and aerosol optical depth are compared. Differences among models are significant for all aerosol types. The largest differences were found near expected source regions of biomass burning ( carbon) and dust. Assumptions for the permitted water uptake also contribute to optical depth differences ( of sulfate, organic carbon, and sea salt) at higher latitudes. The decline of mass or optical depth away from recognized sources reveals strong differences in aerosol transport or removal among models. These differences are also a function of altitude, as transport biases of dust do not always extend to other aerosol types. Ratios of optical depth and mass demonstrate large differences in the mass extinction efficiency, even for hydrophobic aerosol. This suggests that efforts of good mass simulations could be wasted or that conversions are misused to cover for poor mass simulations. In an attempt to provide an absolute measure for model skill, simulated total optical depths ( when adding contributions from all five aerosol types) are compared to measurements from ground and space. Comparisons to the Aerosol Robotic Network (AERONET) suggest a source strength underestimate in many models, most frequently for ( subtropical) tropical biomass or dust. Comparisons to the combined best of Moderate-Resolution Imaging Spectroradiometer ( MODIS) and Total Ozone Mapping Spectrometer ( TOMS) indicate that away from sources, model simulations are usually smaller. Particularly large are discrepancies over tropical oceans and oceans of the Southern Hemisphere, raising issues on the treatment of sea salt in models. Totals for mass or optical depth in many models are defined by the absence or dominance of only one aerosol component. With appropriate corrections to that component ( e. g., to removal, to source strength, or to seasonality) a much better model performance can be expected. Still, many important modeling issues remain inconclusive as the combined result of poor coordination ( different emissions and meteorology), insufficient model output ( vertical distributions, water uptake by aerosol type), and unresolved measurement issues ( retrieval assumptions and temporal or spatial sampling biases).

DOI： 10.1029/2001JD001253

Language：English   Publishing type：Research paper (scientific journal)  

[1] The regional-scale aerosol transport model (CFORS) is used in the analysis of black carbon (BC) observed at five remote Japanese islands during the ACE-Asia experiment. BC is modeled online in the regional-scale meteorological model, using emissions estimates for 2000. Two model experiments are conducted (1) a control run that includes all the BC emission, and (2) a sensitivity run without open biomass burning emissions to clarify the impact of biomass burning on the BC levels in the western Pacific. The regional aerosol model (CFORS) is shown to accurately reproduce many of the important features observed. Model analysis shows that the spatial and temporal distributions of black carbon between the northern sites (Rishiri and Sado; located in the Japan Sea) and the southern stations (Hachijo, Chichijima, and Amami-Oshima; in the western Pacific Ocean) are under different flow regimes. It is shown that the major synoptic features controlling BC levels are associated with outflow in the warm conveyor belt of traveling cold fronts and the subsequent postfrontal transport. At the northern stations (Rishiri and Sado), elevated BC concentrations are calculated to be mainly below the heights of 2000 m, and the biomass burning fraction is estimated to be below 20&#37;. At the southern sites (e.g., Chichijima) the contribution due to biomass burning reaches 32&#37; at the surface and 52&#37; in the free atmosphere. CFORS results indicate that the major black carbon source and transport height are different between the northern and southern sites.

DOI： 10.1029/2002JD003252

Language：Japanese   Publishing type：Research paper (scientific journal)  

A study of aerosol distribution and radiative forcing with a global three-dimensional aerosol transport-radiation model

Language：English   Publishing type：Research paper (scientific journal)  

Aerosols affect the global budgets of O-3, OH, and CH4 in part through their alteration of photolysis rates and in part through their direct chemical interactions with gases (i.e., "heterogeneous chemistry''). The first effect is evaluated here with a global tropospheric chemistry transport model using recently developed global climatologies of tropospheric aerosols: a satellite-derived aerosol climatology over the oceans by advanced very high resolution radiometer and a model-generated climatology for land plus oceans by the Center for Climate System Research. Globally averaged, the impact of aerosols on photolysis alone is to increase tropospheric O-3 by 0.63 Dobson units and increase tropospheric CH4 by 130 ppb (via tropospheric OH decreases of 8&#37;). These greenhouse gas increases lead to an aerosol indirect effect (counting both natural and anthropogenic aerosols) of +0.08 W/m(2). Although the CH4 increases are, of course, global, the changes in tropospheric OH and O-3 are mainly regional, with the largest impacts in northwest Africa for January and in India and southern Africa for July. The influence of aerosols is greater in July than in January and greater in the Northern Hemisphere than in the Southern Hemisphere, as expected given the pollution sources in the Northern Hemisphere. The predominant impact is due to the aerosols over land; aerosols over the ocean contribute less than a third to globally integrated changes.

DOI： 10.1029/2002JD002743

Language：English   Publishing type：Research paper (international conference proceedings)  

Global distributions of the aerosol optical thickness, Angstrom exponent, single scattering albedo, and radiative forcing are simulated by an aerosol climate model, SPRINTARS. All the main tropospheric aerosols are treated, that is, carbonaceous (black and organic carbons), sulfate, soil dust, and sea salt. The global and annual mean radiative forcing of anthropogenic aerosols is estimated to be -0.18 W m(-2) for the direct effect and -1.02 W m(-2) for the indirect effect. The large scale Asian dust storm, transported to the North Pacific, is also successfully simulated by the SPRINTARS.

Language：English   Publishing type：Research paper (scientific journal)  

The broad climatological features associated with the Asian monsoon circulation, including its mean state and intraseasonal and interannual variability over the Indian subcontinent, as simulated in the CCSR/NIES coupled A-O GCM in its control experiment are presented in this paper. The model reproduces the seasonal cycle as well as basic observed patterns of key climatic parameters, in spite of some limitations in simulation of the monsoon rainfall. While the seasonality in rainfall over the region is well simulated and the simulated area-averaged monsoon rainfall is only marginally higher than the observed rainfall, the peak rainfall is simulated to be about two-thirds of the observed precipitation intensity over central India.
The transient experiments performed with the model following the four SRES 'Marker' emission scenarios, which include revised trends for all the principal anthropogenic forcing agents for the future suggest an annual mean area-averaged surface warming over the Indian subcontinent to range between 3.5 and 5.5 degreesC over the region during 2080s. During winter, India may experience between 5 and 25&#37; decline in rainfall. The decline in wintertime-rainfall over India is likely to be significant and may lead to droughts during the dry summer months. Only a 10 to 15&#37; increase is projected in area-averaged summer monsoon rainfall over the Indian subcontinent. The date of onset of summer monsoon over India could become more variable in future.

Language：English   Publishing type：Research paper (scientific journal)  

Statistics from sky/sunphotometers at AERONET sites throughout the world provide the background for a comparison of monthly or seasonally averaged aerosol optical depths to retrievals by operational satellites and to representations in global models. Available data-sets, however, rarely relate to the same year(s). With strong year-to-year variations even for monthly averaged aerosol optical depths and open issues on sampling biases and regional representation by local measurements only larger discrepancies are investigated. Aerosol optical depths retrievals of five different satellites and five different global models are compared. Quantitative accurate satellite retrievals over land remain a challenge and even their relative difference cannot provide clear answers on regional representation. Model predicted aerosol optical depth averages are usually smaller than AERONET. The behavior of models is further explored on a component basis. For sulfate, dust, carbon and sea-salt optical depths, mass and assumed aerosol sizes are compared. For the conversion of the column (dry) component mass in optical depth in models, assumptions for component aerosol size and aerosol humidification are critical. Statistical comparisons to ground-based monitoring will be more useful, if temporal differences are removed. This requires data from the same time-period and the use of sampling screens, to accommodate less frequent measurements. For the understanding of regional representation by local measurements, satellite data play a key role. Necessities to validate critical aerosol assumptions in models or satellite retrievals require field- experiments that focus on individual aerosol components plus continued and additional monitoring (e.g. AERONET) at sites, where a particular aerosol component dominates.

Language：English   Publishing type：Research paper (international conference proceedings)  

Numerical experiment was performed using an general circulation model (GCM) including aerosol indirect effect into water cloud and the simulated global distribution of cloud droplet radii was compared with the global distribution of cloud effective radii retrieved from Advanced Very High Resolution Radiometer (AVHRR).
Comparisons of GCM calculation with AVHRR retrieval showed that our GCM generally can simulate the global characteristics of cloud droplet radii such as a land-sea contrast associated with difference of aerosol abundance and costal region feature due to aerosol injection from adjacent continental area.
AVHRR retrieval and GCM simulation, however, are turned out to show disagreement over tropical region. AVHRR retrieval may tend to overestimate droplet radii due to the contamination of signal by drizzles and ice particles, whereas our GCM does not treat aerosol indirect effect in deep convective clouds predominant over tropics.
Over equatorial central Pacific, where satellite retrieval may suffer from statistical biases, satellite retrieval and GCM simulation are also found to be different.

DOI： 10.1117/12.416976

Language：English   Publishing type：Research paper (international conference proceedings)  

A global three-dimensional transport model that can simultaneously treat main tropospheric aerosols, i.e., carbonaceous (organic and black carbons), sulfate, soil dust, and sea salt, is developed. It is coupled with an Center for Climate System Research (CCSR)/National Institute for Environmental Studies (NIES) atmospheric general circulation model (AGCM), and the meteorological field of wind, temperature, and specific humidity can be nudged by reanalysis data. Simulated results are compared with not only observations for aerosol concentrations but also the optical thickness and Angstrom exponent retrieved from remote sensing data such as National Oceanic and Atmospheric Administration (NOAA)/Advanced Very High Resolution Radiometer (AVHRR) and Aerosol Robotic Network (AERONET). A general agreement is found between simulated results and observations spatially seasonally, and quantitatively. The present model is also coupled with the radiative process over both the solar and thermal regions. The annual and global mean radiative forcing by anthropogenic aerosols from fossil fuel sources is estimated to be -0.5 W m(-2) over the clear sky for the direct effect and -2.0 W m(-2) for the indirect effect.

DOI： 10.1117/12.416964

Language：English   Publishing type：Research paper (international conference proceedings)  

A global three-dimensional transport model that can simultaneously treat main tropospheric aerosols, i.e., carbonaceous (organic and black carbon), sulfate, soil dust, and sea salt, is developed. It is coupled with an atmospheric general circulation model, and the meteorological field such as wind, temperature, and specific humidity used in the model can be nudged by reanalysis data. Simulated results are compared with not only observations for aerosol concentrations but also the optical thickness and Angstroin exponent retrieved from remote sensing data. A general agreement is found between simulated results and observations spatially and seasonally. The present model can also calculate the single scattering albedo and the radiative forcing for a mixed state of various aerosol species. The single scattering albedo is estimated to be close to 1 over remote ocean, from 0.8 to 0.9 over land, and about 0.8 over desert and biomass burning regions, which is consistent with optical observations. It is suggested that the direct radiative forcing of aerosol particles absorbing the solar radiation is sensitive to surface albedo, cloud amounts, and altitudes of cloud layers.

Responsible for pages：総ページ数：1535   Language：English  

Climate Change 2013: The Physical Science Basis, Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change

Responsible for pages：担当ページ数：139-157   Language：Japanese  

Language：English  

Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change

Event date： 2022.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2022.2

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：オンライン   Country：Japan  

Event date： 2021.12

Language：English   Presentation type：Oral presentation (general)  

Venue：online   Country：Other  

Event date： 2021.8

Language：Japanese  

Country：Other  

Event date： 2021.5

Language：Japanese  

Country：Other  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Country：Other  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Lessons learned from emission fluctuation of greenhouse gases and air pollutants due to restrictions associated with the COVID-19 pandemic

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Dependency of surface air temperature change by sulfate aerosols on CO₂ concentration

Event date： 2017.10 - 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台国際センター   Country：Japan  

Event date： 2017.9

Language：English  

Country：Other  

Temperature responses of anthropogenic aerosols assessed with a coupled-ocean general circulation model

Event date： 2015.12

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco, CA   Country：United States  

Event date： 2014.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Yokohama   Country：Japan  

Event date： 2009.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Event date： 2008.10

Language：Others   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：Zurich   Country：Switzerland  

Event date： 2004.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan   Country：Korea, Republic of  

Event date： 2002.10

Language：Others   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2001.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Event date： 2000.5

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：つくば   Country：Japan  

Event date： 2000.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば   Country：Japan  

Event date： 1999.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 1998.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台   Country：Japan  

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Hangzhou   Country：China  

Language：English   Presentation type：Oral presentation (general)  

Venue：Wien, Austria   Country：Other  

Three-dimensional simulation and radiative forcing of various tropospheric aerosols with atmospheric general circulation model

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Taipei, Taiwan   Country：Other  

A global modeling of aerosol radiative characteristics

Language：English   Presentation type：Oral presentation (general)  

Venue：Sendai, Japan   Country：Other  

Global three-dimensional simulation and radiative forcing of various aerosol species with GCM

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岐阜   Country：Other  

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：San Francisco, CA, USA   Country：Other  

Modeling study of aerosol global distribution and radiative forcing

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：大宮   Country：Other  

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Ogden, UT, USA   Country：Other  

Global distributions of aerosol optical properties simulated with the SPRINTARS

Language：Japanese  

Venue：東京   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo, Japan   Country：Other  

Simulation of global aerosol transport-radiative processes based on atmospheric general circulation model

Language：English   Presentation type：Oral presentation (general)  

Venue：Miyazaki, Japan   Country：Other  

Simulation during APEX-E1 and APEX-E2/ACE-Asia by regional and global aerosol models

Language：English   Presentation type：Symposium, workshop panel (public)  

Venue：Crete, Greece   Country：Other  

Simulation of aerosol distributions during ACE-Asia and APEX-E2 with the SPRINTARS

Language：Japanese  

Venue：札幌   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco, CA, USA   Country：Other  

Distribution and radiative forcing of Asian dust and anthropogenic aerosols from East Asia simulated by SPRINTARS

Language：English   Presentation type：Oral presentation (general)  

Venue：Awajishima, Japan   Country：Other  

Analysis of aerosol-climate interaction in East Asia by SPRINTARS

Language：English   Presentation type：Oral presentation (general)  

Venue：Paris, France   Country：Other  

Overview of SPRINTARS

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo, Japan   Country：Other  

Analysis of aerosol-climate interaction by on-line aerosol transport-radiation model

Language：English   Presentation type：Oral presentation (general)  

Venue：Paris, France   Country：Other  

Aerosol radiation-transport model on Earth Simulator

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台   Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco, CA, USA   Country：Other  

Analysis of climate response to aerosol direct and indirect effects by aerosol transport radiation model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：豊川   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Ispra, Italy   Country：Other  

Climate response to aerosol direct and indirect effects with global aerosol radiation-transport model

Language：English   Presentation type：Oral presentation (general)  

Venue：Huelva, Spain   Country：Other  

Analysis of climate change by aerosol direct and indirect effects with aerosol transport radiation model

Language：English   Presentation type：Oral presentation (general)  

Venue：Bologna, Italy   Country：Other  

Analysis of climate change by aerosol direct and indirect effects with aerosol transport-radiation model

Language：English  

Country：Other  

Language：English  

Venue：Busan, Korea   Country：Other  

Development of global aerosol transport-radiation model (lecture on IRC Young Scientist Award)

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan, Korea   Country：Other  

Simulation of climate change by aerosol direct and indirect effects with aerosol transport-radiation model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco, CA, USA   Country：Other  

Modeling study of aerosol effects on climate system under comparisons with satellite retrievals

Language：English   Presentation type：Oral presentation (general)  

Venue：New York, NY, USA   Country：Other  

Simulation of climate response to aerosol direct and indirect effects with aerosol transport-radiation model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神戸   Country：Other  

Language：Japanese  

Venue：柏   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Vienna, Austria   Country：Other  

Simulation of aerosol effects on cloud and precipitation formation by aerosol climate model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Santa Fe, NM, USA   Country：Other  

Aerosol effects on climate system simulated by aerosol climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：Madison, WI, USA   Country：Other  

Simulation of aerosol effects on climate system by aerosol climate model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Virginia Beach, VA, USA   Country：Other  

Analysis of aerosol effects on climate system with a aerosol climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka, Japan   Country：Other  

Analysis of aerosol effects on climate system and time evolutions of various radiative forcings with a global climate model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Greenbelt, MD, USA   Country：Other  

A study of aerosol effects on climate with a general circulation model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Perugia, Italy   Country：Other  

Changes in cloud and precipitation formations by anthropogenic aerosols in Asian region

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：和光   Country：Other  

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：New London, NH, USA   Country：Other  

A Study of aerosol effects on climate with a general circulation model and satellite observations

Language：English   Presentation type：Oral presentation (general)  

Venue：Lille, France   Country：Other  

Simulation of aerosol effects on climate system in Asia

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Hamburg, Germany   Country：Other  

Aerosol effects on climate system simulated by aerosol climate model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：横浜   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Shanghai, China   Country：Other  

Evaluating climate effects and developing forecast system of atmospheric aerosols

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Stockholm, Sweden   Country：Other  

Aerosol effects on climate system: past, present, and future

Language：English   Presentation type：Oral presentation (general)  

Venue：Reykjavik, Iceland   Country：Other  

Distributions and radiative forcings of aerosols during the 21st century

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台   Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Other  

Language：English  

Venue：Kyoto, Japan   Country：Other  

Comparison and data assimilation for global aerosol climate model with measured data from active sensors

Language：English   Presentation type：Oral presentation (general)  

Venue：Davos, Switzerland   Country：Other  

Development of global aerosol forecasting system

Language：English   Presentation type：Oral presentation (general)  

Venue：Princeton, NJ, USA   Country：Other  

Long-term trend of aerosol radiative forcing estimated with different emission inventories

Language：English   Presentation type：Oral presentation (general)  

Venue：Tsukuba, Japan   Country：Other  

Hindcast simulation of aerosol global distribution and radiative forcing with aerosol climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco, CA, USA   Country：Other  

Trend of surface solar radiation over Asia simulated by aerosol transport-climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：Chiba   Country：Other  

Simulation of decadal trends in atmospheric aerosols and their radiative effects in Asia

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Portland, OR, USA   Country：Other  

Decadal-scale trend of surface solar radiation simulated by a global aerosol transport-climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：Seoul, Korea   Country：Other  

Analysis of decadal trend of surface solar radiation in Asia simulated by an aerosol transport-climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：Oxford, UK   Country：Other  

Change in surface solar radiation due to aerosols for several decades based on AeroCom Phase II Experiment

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Okinawa, Japan   Country：Other  

Evaluation and data assimilation of aerosol distributions and climate effects simulated by SPRINTARS using remote sensing observations in the Asian region

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Melbourne, Australia   Country：Other  

Projection of climate change by the aerosol direct and Indirect effects in the 21st century

Language：English   Presentation type：Oral presentation (general)  

Venue：Prague, Czech Republic   Country：Other  

Projection of future climate change by aerosols along the Representative Concentration Pathways (RCPs) with a global climate model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：春日   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Bonn, Germany   Country：Other  

Implications for common metrics of short-lived climate forcers (SLCFs)

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば   Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉   Country：Other  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Berlin, Germany   Country：Other  

Historical and future simulations of aerosol radiative forcing along the Representative Concentration Pathways (RCPs) with a global climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：Leipzig, Germany   Country：Other  

Historical and future simulations of aerosol climate effects with a global climate model

Language：English   Presentation type：Oral presentation (general)  

Venue：Seattle, WA, USA   Country：Other  

Distributions and climate effects of atmospheric aerosols from 1850 to 2100 along Representative Concentration Pathways (RCPs) simulated by SPRINTARS

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Busan, Korea   Country：Other  

Historical and future aerosol radiative forcing along the Representative Concentration Pathways (RCPs) with the global climate model

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Hamburg, Germany   Country：Other  

Recent topics using aerosol models —focusing on Japanese activities—

Language：English   Presentation type：Oral presentation (general)  

Venue：Seoul, Korea   Country：Other  

Recent studies on the aerosol-climate interaction with global models

Language：Japanese  

Venue：仙台   Country：Other  

Language：English  

Venue：Yokohama, Japan   Country：Other  

SPRINTARS global aerosol forecasting system and introduction of S-12 project

Language：English   Presentation type：Oral presentation (general)  

Venue：Yokohama, Japan   Country：Other  

Introduction of IPCC WG1 AR5 and S-12 project related to short-lived climate pollutants

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo, Japan   Country：Other  

Recent studies on effects of aerosols on the climate system with global climate models

Language：English   Presentation type：Oral presentation (general)  

Venue：Sapporo, Japan   Country：Other  

Perspective of researches on aerosol climate effects with global climate models

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo, Japan   Country：Other  

Application of EarthCARE data in climate models for studies on climate change and air pollution by aerosols

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Venue：Steamboat Springs, CO, USA   Country：Other  

Relative contributions of regional emissions to the aerosol radiative forcing based on the AeroCom Phase III / HTAP2 experiment

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco, CA, USA   Country：Other  

Relative contributions of regional and sector emissions to the radiative forcing of aerosol-radiation and aerosol-cloud interactions based on the AeroCom Phase III / HTAP2 experiment

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other  

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Simulations under recent projects on aerosol model intercomparisons

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Integrated assessment on effects of short-lived climate pollutants (SLCPs) in Asia

Language：English  

Country：Other  

Integrated assessment on effects of short-lived climate pollutants (SLCPs) in Asia based on numerical models

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Assessment on climate response to aerosol effects based on a coupled atmosphere-ocean general circulation model

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Resent application of SKYNET and AD-Net to aerosol climate models

Language：English   Presentation type：Oral presentation (general)  

Country：Other  

Environmental assessment on aerosol effects in Asian region based on modeling studies

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Other