Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Takashi Mochizuki Last modified date:2024.04.11

Associate Professor / Department of Earth and Planetary Sciences / Faculty of Sciences

1. Tsuchida, K., T. Mochizuki, R. Kawamura, T. Kawano, Interdecadal variations of radiative feedbacks associated with the El Niño and Southern Oscillation (ENSO) in CMIP6 models, Geophysical Research Letters, 10.1029/2023GL106127, 2023.11.
2. Tsuchida, K., T. Mochizuki, R. Kawamura, T. Kawano, Y. Kamae, Diversity of lagged relationships in global means of surface temperatures and radiative budgets for CMIP6 piControl simulations, Journal of Climate, 10.1175/JCLI-D-23-0045.1, 2023.10.
3. Zhang, X., T. Mochizuki, Decadal modulation of ENSO and IOD impacts on the Indian Ocean upwelling, Frontiers in Earth Science, 10.3389/feart.2023.1212421, 2023.08.
4. Yoshida, N., R. Kawamura, T. Kawano, T. Mochizuki, S. Iizuka, Remote dynamic and thermodynamic effects of typhoons on Meiyu–Baiu precipitation in Japan assessed with bogus typhoon experiments, Weather and Climate Extremes, 10.1016/j.wace.2023.100578, 2023.05.
5. Kawano, T., R. Yasukiyo, R. Kawamura, T. Mochizuki, A Projection of Future JPCZs by WRF Dynamical Downscaling Simulations based on MIROC6 ScenarioMIP ssp585, Scientific Online Letters on the Atmosphere, 10.2151/sola. 2023-014, 2023.05.
6. Mochizuki, T., M. Watanabe, Atlantic impacts on subdecadal warming over the tropical Pacific in the 2000s, Frontiers in Climate, 10.3389/fclim.2022.1040352, 2022.11.
7. Zhang, X., T. Mochizuki, Sea surface height fluctuations relevant to Indian summer monsoon over the northwestern Indian Ocean, Frontiers in Climate, 10.3389/fclim.2022.1008776, 2022.11.
8. Suzuki, Y., R. Kawamura, T. Kawano, T. Mochizuki , Cascading effects of the Changbai Mountains on an extreme weather disaster in northern Japan in January 2021, Weather and Climate Extremes, 10.1016/j.wace.2022.100439, 36, 100439, 2022.04.
9. Chikamoto, Y., Z. F. Johnson, S.-Y. Wang, M. J. McPhaden, T. Mochizuki, El Niño-Southern Oscillation Evolution Modulated by Atlantic Forcing, CLIVAR Exchanges, 10.36071/clivar.80.2021, 80, 12-15, 2021.08.
10. Kataoka, T., T. Tatebe, H. Koyama, T. Mochizuki, K. Ogochi, H. Naoe, Y. Imada, H. Shiogama, M. Kimoto, M. Watanabe, Seasonal to decadal predictions with MIROC6: Description and basic evaluation, Journal of Advances in Modeling Earth Systems, 10.1029/2019MS002035, 2020.10.
11. Smith, D. M., A. A. Scaife, R. Eade, P. Athanasiadis, A. Bellucci, I. Bethke, R. Bilbao, L. F. Borchert, L.-P. Caron, F. Counillon, G. Danabasoglu, T. Delworth, F. J. Doblas-Reyes, N. J. Dunstone, V. Estella-Perez, S. Flavoni, L. Hermanson, N. Keenlyside, V. Kharin, M. Kimoto, W. J. Merryfield, J. Mignot, T. Mochizuki, K. Modali, P.-A. Monerie, W. A. Muller, D. Nicoli, P. Ortega, K. Pankatz, H. Pohlmann, J. Robson, P. Ruggieri, R. Sospedra-Alfonso, D. Swingedouw, Y. Wang, S. Wild, S. Yeager, X. Yang, L. Zhang, North Atlantic climate far more predictable than models imply, Nature, 10.1038/s41586-020-2525-0, 583, 796-800, 2020.07.
12. Chikamoto, Y., Z. F. Johnson, S.-Y. Wang, M. J. McPhaden, T. Mochizuki, El Nino Southern Oscillation evolution modulated by the Atlantic forcing, Journal of Geophysical Research - Oceans, 10.1029/2020JC016318, 2020.07.
13. Johnson, Z. F., Y. Chikamoto, S.-Y. Wang, M. J. McPhaden, T. Mochizuki, Pacific Decadal Oscillation remotely forced by the equatorial Pacific and the Atlantic Oceans, Climate Dynamics, 10.1007/s00382-020-05295-2, 55, 789-811, 2020.06.
14. Y. Qian, H. Murakami, M. Nakano, P. C. Hsu, T. L. Delworth, S. B. Kapnick, V. Ramaswamy, T. Mochizuki, Y. Morioka, T. Doi, T. Kataoka, T. Nasuno, K. Yoshida, On the Mechanisms of the Active 2018 Tropical Cyclone Season in the North Pacific, Geophysical Research Letters, 10.1029/2019GL084566, 46, 21, 12293-12302, 2019.11, The 2018 tropical cyclone (TC) season in the North Pacific was very active, with 39 tropical storms including eight typhoons/hurricanes. This activity was successfully predicted up to 5 months in advance by the Geophysical Fluid Dynamics Laboratory Forecast-Oriented Low Ocean Resolution (FLOR) global coupled model. In this work, a suite of idealized experiments with three dynamical global models (FLOR, Nonhydrostatic Icosahedral Atmospheric Model, and Meteorological Research Institute Atmospheric General Circulation Model) was used to show that the active 2018 TC season was primarily caused by warming in the subtropical Pacific and secondarily by warming in the tropical Pacific. Furthermore, the potential effect of anthropogenic forcing on the active 2018 TC season was investigated using two of the global models (FLOR and Meteorological Research Institute Atmospheric General Circulation Model). The models projected opposite signs for the changes in TC frequency in the North Pacific by an increase in anthropogenic forcing, thereby highlighting the substantial uncertainty and model dependence in the possible impact of anthropogenic forcing on Pacific TC activity..
15. Hiroaki Tatebe, Tomoo Ogura, Tomoko Nitta, Yoshiki Komuro, Koji Ogochi, Toshihiko Takemura, Kengo Sudo, Miho Sekiguchi, Manabu Abe, Fuyuki Saito, Minoru Chikira, Shingo Watanabe, Masato Mori, Nagio Hirota, Yoshio Kawatani, Takashi Mochizuki, Kei Yoshimura, Kumiko Takata, Ryouta O'Ishi, Dai Yamazaki, Tatsuo Suzuki, Masao Kurogi, Takahito Kataoka, Masahiro Watanabe, Masahide Kimoto, Description and basic evaluation of simulated mean state, internal variability, and climate sensitivity in MIROC6, Geoscientific Model Development, 10.5194/gmd-12-2727-2019, 12, 7, 2727-2765, 2019.07, 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..
16. D. M. Smith, R. Eade, A. A. Scaife, L.-P. Caron, T. M. Delsole, G. Danabasoglu, T. Delworth, F. J. Doblas-Reyes, N. J. Dunstone, L. Hermanson, V. Kharin, M. Kimoto, W. J. Merryfield, T. Mochizuki, W. A. Muller, H. Pohlmann, S. Yeager, X. Yang, Robust skill of decadal climate predictions, npj Climate and Atmospheric Science, 10.1038/s41612-019-0071-y, 2, 13, 2019.05.
17. Takashi Mochizuki, Masahiro Watanabe, Observed and hindcasted subdecadal variability of the tropical Pacific climate, ICES Journal of Marine Science, 10.1093/icesjms/fsz026, 2019.02.
18. D. M. Smith, A. A. Scaife, E. Hawkins, R. Bilbao, G. J. Boer, M. Caian, L. P. Caron, G. Danabasoglu, T. Delworth, F. J. Doblas-Reyes, R. Doescher, N. J. Dunstone, R. Eade, L. Hermanson, M. Ishii, V. Kharin, M. Kimoto, T. Koenigk, Y. Kushnir, D. Matei, G. A. Meehl, M. Menegoz, W. J. Merryfield, Takashi Mochizuki, W. A. Müller, H. Pohlmann, S. Power, M. Rixen, R. Sospedra-Alfonso, M. Tuma, K. Wyser, X. Yang, S. Yeager, Predicted Chance That Global Warming Will Temporarily Exceed 1.5 °C, Geophysical Research Letters, 10.1029/2018GL079362, 45, 21, 11,895-11,903, 2018.11, The Paris Agreement calls for efforts to limit anthropogenic global warming to less than 1.5 °C above preindustrial levels. However, natural internal variability may exacerbate anthropogenic warming to produce temporary excursions above 1.5 °C. Such excursions would not necessarily exceed the Paris Agreement, but would provide a warning that the threshold is being approached. Here we develop a new capability to predict the probability that global temperature will exceed 1.5 °C above preindustrial levels in the coming 5 years. For the period 2017 to 2021 we predict a 38% and 10% chance, respectively, of monthly or yearly temperatures exceeding 1.5 °C, with virtually no chance of the 5-year mean being above the threshold. Our forecasts will be updated annually to provide policy makers with advanced warning of the evolving probability and duration of future warming events..
19. Zachary F. Johnson, Yoshimitsu Chikamoto, Jing Jia Luo, Takashi Mochizuki, Ocean impacts on Australian interannual to decadal precipitation variability, Climate, 10.3390/cli6030061, 6, 3, 2018.09, In Australia, successful seasonal predictions of wet and dry conditions are achieved by utilizing the remote impact of sea surface temperature (SST) variability in tropical oceans, particularly the Pacific Ocean, on the seasonal timescale. Beyond seasonal timescales, however, it is still unclear which processes and oceans contribute to interannual-to-decadal wet/dry conditions in Australia. This research examines the interannual-to-decadal relationship between global SST anomalies (SSTAs) and Australian wet/dry variability by analyzing observational data and global climate model experiments conducted with the NCAR Community Earth System Model (CESM) and the Model for Interdisciplinary Research on Climate (MIROC). A 10-member ensemble simulation suite for 1960-2015 (CESM) and 1950-2010 (MIROC) is conducted by assimilating the observed three-dimensional ocean temperature and salinity anomalies into fully coupled global climate models. In both observational analyses and ocean assimilation experiments, the most dominant annual mean precipitation variability shows a clear relationship with SSTAs in the tropical Pacific and the Atlantic. Our partial ocean assimilation experiment, in which the ocean component of the CESM and MIROC are assimilated by the observed ocean temperature and salinity anomalies in the equatorial Pacific only, shows that the tropical Pacific SST variability is the main driver of Australian precipitation variability on the interannual-to-decadal timescales. However, our additional partial ocean assimilation experiment, in which the climate models incorporate the observed anomalies solely in the Atlantic ocean, demonstrates that the Atlantic Ocean can also affect Australian precipitation variability on the interannual-to-decadal timescale through changes in tropical Pacific SSTAs and the modulation of the globalWalker circulation. Our results suggest that about a half of Australian interannual-to-decadal precipitation variability originates from the Atlantic Ocean..
20. Yoo Geun Ham, Yoshimitsu Chikamoto, Jong Seong Kug, Masahide Kimoto, Takashi Mochizuki, Tropical Atlantic-Korea teleconnection pattern during boreal summer season, Climate Dynamics, 10.1007/s00382-016-3474-z, 49, 7-8, 2649-2664, 2017.10, The remote impact of tropical Atlantic sea surface temperature (SST) variability on Korean summer precipitation is examined based on observational data analysis along with the idealized and hindcast model experiments. Observations show a significant correlation (i.e. 0.64) between Korean precipitation anomalies (averaged over 120–130°E, 35–40°N) and the tropical Atlantic SST index (averaged over 60°W–20°E, 30°S–30°N) during the June–July–August (JJA) season for the 1979–2010 period. Our observational analysis and partial-data assimilation experiments using the coupled general circulation model demonstrate that tropical Atlantic SST warming induces the equatorial low-level easterly over the western Pacific through a reorganization of the global Walker Circulation, causing a decreased precipitation over the off-equatorial western Pacific. As a Gill-type response to this diabatic forcing, an anomalous low-level anticyclonic circulation appears over the Philippine Sea, which transports wet air from the tropics to East Asia through low-level southerly, resulting an enhanced precipitation in the Korean peninsula. Multi-model hindcast experiments also show that predictive skills of Korean summer precipitation are improved by utilizing predictions of tropical Atlantic SST anomalies as a predictor for Korean precipitation anomalies..
21. Xueyuan Liu, Armin Köhl, Detlef Stammer, Shuhei Masuda, Yoichi Ishikawa, Takashi Mochizuki, Impact of in-consistency between the climate model and its initial conditions on climate prediction, Climate Dynamics, 10.1007/s00382-016-3194-4, 49, 3, 1061-1075, 2017.08, We investigated the influence of dynamical in-consistency of initial conditions on the predictive skill of decadal climate predictions. The investigation builds on the fully coupled global model “Coupled GCM for Earth Simulator” (CFES). In two separate experiments, the ocean component of the coupled model is full-field initialized with two different initial fields from either the same coupled model CFES or the GECCO2 Ocean Synthesis while the atmosphere is initialized from CFES in both cases. Differences between both experiments show that higher SST forecast skill is obtained when initializing with coupled data assimilation initial conditions (CIH) instead of those from GECCO2 (GIH), with the most significant difference in skill obtained over the tropical Pacific at lead year one. High predictive skill of SST over the tropical Pacific seen in CIH reflects the good reproduction of El Niño events at lead year one. In contrast, GIH produces additional erroneous El Niño events. The tropical Pacific skill differences between both runs can be rationalized in terms of the zonal momentum balance between the wind stress and pressure gradient force, which characterizes the upper equatorial Pacific. In GIH, the differences between the oceanic and atmospheric state at initial time leads to imbalance between the zonal wind stress and pressure gradient force over the equatorial Pacific, which leads to the additional pseudo El Niño events and explains reduced predictive skill. The balance can be reestablished if anomaly initialization strategy is applied with GECCO2 initial conditions and improved predictive skill in the tropical Pacific is observed at lead year one. However, initializing the coupled model with self-consistent initial conditions leads to the highest skill of climate prediction in the tropical Pacific by preserving the momentum balance between zonal wind stress and pressure gradient force along the equatorial Pacific..
22. Takashi Mochizuki, Masahide Kimoto, Masahiro Watanabe, Yoshimitsu Chikamoto, Masayoshi Ishii, Interbasin effects of the Indian Ocean on Pacific decadal climate change, Geophysical Research Letters, 10.1002/2016GL069940, 43, 13, 7168-7175, 2016.07.
23. Y. Chikamoto, Takashi Mochizuki, A. Timmermann, M. Kimoto, M. Watanabe, Potential tropical Atlantic impacts on Pacific decadal climate trends, Geophysical Research Letters, 10.1002/2016GL069544, 43, 13, 7143-7151, 2016.07, The tropical Pacific cooling from the early 1990s to 2013 has contributed to the slowdown of globally averaged sea surface temperatures (SSTs). The origin of this regional cooling trend still remains elusive. Here we demonstrate that the remote impact of Atlantic SST anomalies, as well as local atmosphere-ocean interactions, contributed to the eastern Pacific cooling during this period. By assimilating observed three-dimensional Atlantic temperature and salinity anomalies into a coupled general circulation model, we are able to qualitatively reproduce the observed Pacific decadal trends of SST and sea level pressure (SLP), albeit with reduced amplitude. Although a major part of the Pacific SLP trend can be explained by equatorial Pacific SST forcing only, the origin of this low-frequency variability can be traced back further to the remote impacts of equatorial Atlantic and South Atlantic SST trends. Atlantic SST impacts on the atmospheric circulation can also be detected for the Northeastern Pacific, thus providing a linkage between Atlantic climate and Western North American drought conditions..
24. Takashi Mochizuki, Shuhei Masuda, Yoichi Ishikawa, Toshiyuki Awaji, Multiyear climate prediction with initialization based on 4D-Var data assimilation, Geophysical Research Letters, 10.1002/2016GL067895, 43, 8, 3903-3910, 2016.04.
25. Shuhei Masuda, John Philip Matthews, Yoichi Ishikawa, Takashi Mochizuki, Yuusuke Tanaka, Toshiyuki Awaji, A new Approach to El Niño Prediction beyond the Spring Season, Scientific reports, 10.1038/srep16782, 5, 2015.11, The enormous societal importance of accurate El Niño forecasts has long been recognized. Nonetheless, our predictive capabilities were once more shown to be inadequate in 2014 when an El Nino event was widely predicted by international climate centers but failed to materialize. This result highlighted the problem of the opaque spring persistence barrier, which severely restricts longer-term, accurate forecasting beyond boreal spring. Here we show that the role played by tropical seasonality in the evolution of the El Niño is changing on pentadal (five-year) to decadal timescales and thus that El Niño predictions beyond boreal spring will inevitably be uncertain if this change is neglected. To address this problem, our new coupled climate simulation incorporates these long-term influences directly and generates accurate hindcasts for the 7 major historical El Niños. The error value between predicted and observed sea surface temperature (SST) in a specific tropical region (5°N-5°S and 170°-120°W) can consequently be reduced by 0.6 Kelvin for one-year predictions. This correction is substantial since an "El Niño" is confirmed when the SST anomaly becomes greater than +0.5 Kelvin. Our 2014 forecast is in line with the observed development of the tropical climate..
26. Yoshimitsu Chikamoto, Axel Timmermann, Jing Jia Luo, Takashi Mochizuki, Masahide Kimoto, Masahiro Watanabe, Masayoshi Ishii, Shang Ping Xie, Fei Fei Jin, Skilful multi-year predictions of tropical trans-basin climate variability, Nature communications, 10.1038/ncomms7869, 6, 2015.04.
27. Takashi Mochizuki, Masahide Kimoto, Yoshimitsu Chikamoto, Masato Mori, Masahiro Watanabe, Masayoshi Ishii, Error sensitivity to initial climate states in pacific decadal hindcasts, Scientific Online Letters on the Atmosphere, 10.2151/sola.2014-009, 10, 1, 39-44, 2014.01, We perform decadal hindcast experiments with initialization every year and assess sensitivity of the hindcasted errors to the errors in the initial climate states. The hindcasted sea surface temperature (SST) over the extratropical North Pacific shows significant impacts of initialization, yet the hindcasted indices of the Pacific decadal variability usually suffer from limited predictability. Our sensitivity analyses reveal that, in the decadal SST hindcasts over the extratropical North Pacific, the annual-todecadal errors of the Aleutian Low fluctuation before the time of starting hindcast experiments work as a major source of uncertainty through delayed responses of the ocean. As we directly assimilate only the ocean states to the atmosphere-ocean coupled model in initialization, the Aleutian Low fluctuation in the assimilation exhibits large errors even though the SST is well correlated with the observation. These assimilation errors in the Aleutian Low fluctuation are primarily due to the distorted responses of the extratropical atmosphere to the tropical SST changes in the model. A close examination indicates that the observed and assimilated Aleutian Lows are sensitive to the eastern and central equatorial SSTs, respectively. Toward further reducing uncertainty in the Pacific decadal hindcasts, therefore, it should be an effective way to raise quality of initial conditions for the extratropical atmosphere and the tropical atmosphere-ocean coupling..
28. Masato Mori, Masahide Kimoto, Masayoshi Ishii, Satoru Yokoi, Takashi Mochizuki, Yoshimitsu Chikamoto, Masahiro Watanabe, Toru Nozawa, Hiroaki Tatebe, Takashi T. Sakamoto, Yoshiki Komuro, Yukiko Imada, Hiroshi Koyama, Hindcast prediction and near-future projection of tropical cyclone activity over the Western North Pacific using CMIP5 near-term experiments with MIROC, Journal of the Meteorological Society of Japan, 10.2151/jmsj.2013-402, 91, 4, 431-452, 2013.09, In line with the experimental design for near-term climate prediction toward the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, we perform ensembles of initialized decadal hindcast and near-future projection using three versions of the coupled atmosphere-ocean model MIROC. In the present study, we explore interannual and multiyear predictability of tropical cyclone (TC) activity in the western North Pacific (WNP) using the initialized hindcasts and examine global warming impacts on TC activity in the near-future on the basis of near-future projections up to 2035. The hindcasts of year-to-year variation in TC number capture the observed values reasonably well. Moreover, interannual variability of TC genesis and occurrence frequency associated with the El Niño Southern Oscillation are found to be predictable, mainly through better prediction of sea surface temperature (SST) and large-scale vorticity anomalies in the lower troposphere. These results indicate that the models can reproduce the major basic mechanisms that link TC genesis with large-scale circulation. Skillful prediction of TC number is likely difficult on multiyear timescales, at least based on our hindcasts, but through initializations, the three-year-mean hindcasts from 1998 onward reasonably capture observed major characteristics of TC activity associated with Pacific climate shift during the late 1990s. Near-future projections (2016-2035) suggest significant reductions (approximately 14%) in TC number, particularly over the western part of the WNP, even under scenarios in which projected global warming is less prominent than that at the end of this century. This reduction is likely due to the suppression of large-scale lower tropospheric vorticity and relative humidity and the enhancement of vertical wind shear. The projected SST exhibits a more pronounced warming over the eastern tropical Pacific than over the western region and accompanies the weakening of Walker circulation via redistribution of tropical convection activity, which appears to be responsible for the change in the large-scale fields in the WNP..
29. Masahiro Watanabe, Youichi Kamae, Masakazu Yoshimori, Akira Oka, Makiko Sato, Masayoshi Ishii, Takashi Mochizuki, Masahide Kimoto, Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus, Geophysical Research Letters, 10.1002/grl.50541, 40, 12, 3175-3179, 2013.06, The rate of increase of global-mean surface air temperature (SAT
) has apparently slowed during the last decade. We investigated the extent to which state-of-the-art general circulation models (GCMs) can capture this hiatus period by using multimodel ensembles of historical climate simulations. While the SAT
linear trend for the last decade is not captured by their ensemble means regardless of differences in model generation and external forcing, it is barely represented by an 11-member ensemble of a GCM, suggesting an internal origin of the hiatus associated with active heat uptake by the oceans. Besides, we found opposite changes in ocean heat uptake efficiency (κ), weakening in models and strengthening in nature, which explain why the models tend to overestimate the SAT
trend. The weakening of κ commonly found in GCMs seems to be an inevitable response of the climate system to global warming, suggesting the recovery from hiatus in coming decades. Key Points Global-mean SAT trend for 2001-2010 is barely represented by GCM ensembles Ocean heat uptake efficiency is weakening in GCMs and strengthening in nature Weakening of uptake efficiency is inevitable response of forced climate system.
30. F. J. Doblas-Reyes, I. Andreu-Burillo, Y. Chikamoto, J. García-Serrano, V. Guemas, M. Kimoto, Takashi Mochizuki, L. R.L. Rodrigues, G. J. Van Oldenborgh, Initialized near-term regional climate change prediction, Nature communications, 10.1038/ncomms2704, 4, 2013.05.
31. Yoshimitsu Chikamoto, Masahide Kimoto, Masayoshi Ishii, Takashi Mochizuki, Takashi T. Sakamoto, Hiroaki Tatebe, Yoshiki Komuro, Masahiro Watanabe, Toru Nozawa, Hideo Shiogama, Masato Mori, Sayaka Yasunaka, Yukiko Imada, An overview of decadal climate predictability in a multi-model ensemble by climate model MIROC, Climate Dynamics, 10.1007/s00382-012-1351-y, 40, 5-6, 1201-1222, 2013.01, Decadal climate predictability is examined in hindcast experiments by a multi-model ensemble using three versions of the coupled atmosphere-ocean model MIROC. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity with prescribed natural and anthropogenic forcings on the basis of the historical data and future emission scenarios in the Intergovernmental Panel of Climate Change. Results of the multi-model ensemble in our hindcast experiments show that predictability of surface air temperature (SAT) anomalies on decadal timescales mostly originates from externally forced variability. Although the predictable component of internally generated variability has considerably smaller SAT variance than that of externally forced variability, ocean subsurface temperature variability has predictive skills over almost a decade, particularly in the North Pacific and the North Atlantic where dominant signals associated with Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) are observed. Initialization enhances the predictive skills of AMO and PDO indices and slightly improves those of global mean temperature anomalies. Improvement of these predictive skills in the multi-model ensemble is higher than that in a single-model ensemble..
32. Y. Chikamoto, M. Kimoto, M. Watanabe, M. Ishii, Takashi Mochizuki, Relationship between the Pacific and Atlantic stepwise climate change during the 1990s, Geophysical Research Letters, 10.1029/2012GL053901, 39, 21, 2012.11, A linkage between climate change in the Atlantic and the Pacific oceans during the 1990s is investigated using three versions of the coupled climate model MIROC and CMIP5 multi-model ensemble. From the early 1990s to the early 2000s, the observed sea surface temperature (SST) shows warming in the North Atlantic and a La Nia-like pattern in the Pacific. Associated with the SST pattern, the observations indicate a strengthened Walker circulation in the tropical Pacific and enhanced precipitation in the tropical Atlantic. These SST and precipitation patterns are simulated well by hindcast experiments with external forcing and an initialized ocean anomaly state but are poorly simulated by uninitialized simulation with external forcing only. In particular, the observed La Nia-like SST pattern becomes prominent in ensemble members with large amplitudes of Atlantic Multidecadal Oscillation (AMO) index during 1996-1998. Our results suggest that ocean initialization in both the Pacific and the Atlantic plays an important role in predicting the Pacific stepwise climate change during the 1990s, which contributes to the accurate estimation of global temperature change in the coming decade. Forecasting typhoon frequency or marine fisheries production in the coming decade may be possible by improving the predictive skill of stepwise climate change..
33. Takashi Mochizuki, Yoshimitsu Chikamoto, Masahide Kimoto, Masayoshi Ishii, Hiroaki Tatebe, Yoshiki Komuro, Takashi T. Sakamoto, Masahiro Watanabe, Masato Mori, Decadal prediction using a recent series of MIROC global climate models, Journal of the Meteorological Society of Japan, 10.2151/jmsj.2012-A22, 90, A, 373-383, 2012.07.
34. Takashi T. Sakamoto, Yoshiki Komuro, Teruyuki Nishimura, Masayoshi Ishii, Hiroaki Tatebe, Hideo Shiogama, Akira Hasegawa, Takahiro Toyoda, Masato Mori, Tatsuo Suzuki, Yukiko Imada, Toru Nozawa, Kumiko Takata, Takashi Mochizuki, Koji Ogochi, Seita Emori, Hiroyasu Hasumi, Masahide Kimoto, MIROC4h-A new high-resolution atmosphere-ocean coupled general circulation model, Journal of the Meteorological Society of Japan, 10.2151/jmsj.2012-301, 90, 3, 325-359, 2012.07, A new high-resolution atmosphere-ocean coupled general circulation model named MIROC4h has been developed, and its performance in a 120-year control experiment (including a 50-year spin-up) under the present conditions (the year 1950) is examined. The results of the control experiment by MIROC4h are compared with simulations of preindustrial conditions carried out for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) using the previous high- and medium-resolution versions of the model, called MIROC3h and MIROC3m, respectively. A major change in MIROC4h is a doubling of the resolution of the atmospheric component to 0.5625°, compared to 1.125° for MIROC3h. The oceanic components of MIROC4h and MIROC3h are eddy-permitting, with a horizontal resolution of 0.28125° (zonal) × 0.1875° (meridional). In MIROC3m, the horizontal resolution is 2.8125° for the atmospheric component and 1.40625° (zonal) × 0.56°-1.4° (meridional) for the ocean component. Compared with MIROC3h and MIROC3m, many improvements have been achieved; for example, errors in the surface air temperature and sea surface temperature are smaller, there is less drift of the ocean water temperature in the subsurface-deep ocean, and the frequency of heavy rain is comparable to observations. The fine horizontal resolution in the atmosphere makes orographic wind and its effects on the ocean more realistic than those of the former models, and the treatment of coastal upwelling motion in the ocean has been improved. Phenomena in the atmosphere and ocean related to the El Niño and southern oscillation are now closer to observations than was obtained by MIROC3h and MIROC3m. The effective climate sensitivity for CO
doubling is calculated to be about 5.7 K, which is much larger than the value obtained using the IPCC AR4 models, and is mainly due to a decrease in the low-level clouds at low latitudes..
35. Yoshimitsu Chikamoto, Masahide Kimoto, Masayoshi Ishii, Masahiro Watanabe, Toru Nozawa, Takashi Mochizuki, Hiroaki Tatebe, Takashi T. Sakamoto, Yoshiki Komuro, Hideo Shiogama, Masato Mori, Sayaka Yasunaka, Yukiko Imada, Hiroshi Koyama, Masato Nozu, Fei Fei Jin, Predictability of a stepwise shift in Pacific climate during the late 1990s in hindcast experiments using MIROC, Journal of the Meteorological Society of Japan, 10.2151/jmsj.2012-A01, 90, A, 1-21, 2012.07, Sea surface temperature (SST) predictability in the Pacific on decadal timescales is examined in hindcast experiments using the coupled atmosphere-ocean model MIROC with low, medium, and high resolutions. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity while prescribing natural and anthropogenic forcing based on the IPCC concentration scenarios. Our hindcast experiments show the predictability of SST in the western subtropical Pacific, the Indian Ocean, and the tropics to the North Atlantic. Previous studies have examined the SST predictability in the Indian Ocean and the Atlantic, but SST predictability in the western subtropical Pacific has not been evaluated. In the western Pacific, the observed SST anomalies in the subtropics of both hemispheres increased rapidly from the early 1990s to the early 2000s. While this SST warming in the western subtropical Pacific is partly explained by global warming signals, the predictions of our model initialized in 1995 or 1996 tend to simulate the pattern of the SST increase and the associated precipitation changes. This large climate change around the late 1990s may be related to phenomena such as the recent increase in the typhoon frequency in Taiwan and the weakened East Asian monsoon reported by recent studies..
36. Hiroaki Tatebe, Masayoshi Ishii, Takashi Mochizuki, Yoshimitsu Chikamoto, Takashi T. Sakamoto, Yoshiki Komuro, Masato Mori, Sayaka Yasunaka, Masahiro Watanabe, Koji Ogochi, Tatsuo Suzuki, Teruyuki Nishimura, Masahide Kimoto, The initialization of the MIROC climate models with hydrographic data assimilation for decadal prediction, Journal of the Meteorological Society of Japan, 10.2151/jmsj.2012-A14, 90, A, 275-294, 2012.07, This paper documents the procedure of ocean data assimilation that initializes the climate models MIROC3m, MIROC4h, and MIROC5 for decadal climate predictions following the CMIP5 protocol, and summarizes the performance of the climate models using this data assimilation. Only anomalies of observed ocean hydrographic data are assimilated using the incremental analysis update method in order to prevent model climate drifts during predictions. In the case of MIROC4h, which has an eddy-permitting ocean model, a spatial smoother is used in calculating analysis increments so that oceanic mesoscale eddies cannot be damped by observational constraints and that they are generated and decay physically in response to the assimilated background state. Globally, the decadal-scale variations of ocean temperatures in the assimilation runs are highly correlated with the observations. Variations of surface air temperature over oceans are also consistent with the observations, but this is not the case in some regions over continents. Atmospheric responses to the SST variations corresponding to the Pacific Decadal Oscillations and the Atlantic Multi-decadal Oscillation are better represented in MIROC4h and MIROC5 than in MIROC3m. The high resolution of MIROC4h and new cloud parameterizations in MIROC5 may contribute to this improvement. Root-mean-squared amplitudes of sea surface height variations associated with oceanic eddies (hereafter, eddy activity) are not suppressed undesirably in the MIROC4h assimilation run and these are comparable with those in the uninitialized runs. In the Kuroshio-Oyashio confluence zone, eddy activity is modulated on a decadal timescale. This modulation is reasonably represented in the assimilation run compared with the observations. In the hindcast experiments, significant decadal prediction skills are found for the North Atlantic, the subtropical North Pacific, and the Indian Ocean. The decadal climate predictions are expected to contribute to the IPCC AR5 and political decision-making for the coming decades..
37. Sayaka Yasunaka, Masayoshi Ishii, Masahide Kimoto, Takashi Mochizuki, Hideo Shiogama, Influence of XBT temperature bias on decadal climate prediction with a coupled climate model, Journal of Climate, 10.1175/2011JCLI4230.1, 24, 20, 5303-5308, 2011.10, The influence of the expendable bathythermograph (XBT) depth bias correction on decadal climate prediction is presented by using a coupled atmosphere-ocean general circulation model called the Model for Interdisciplinary Research on Climate 3 (MIROC3). The global mean subsurface ocean temperatures that were simulated by the model with the prescribed anthropogenic and natural forcing are consistent with biascorrected observations from the mid-1960s onward, but not with uncorrected observations. The latter is reflected by biases in subsurface ocean temperatures, particularly along thermoclines in the tropics and subtropics. When the correction is not applied to XBT observations, these biases are retained in data assimilation results for the model's initial conditions. Hindcasting past Pacific decadal oscillations (PDOs) is more successful in the experiment with the bias-corrected observations than that without the correction. Improvement of skill in predicting 5-yr mean vertically average ocean subsurface temperature is also seen in the tropical and the central North Pacific where PDO-related signals appear large..
38. Takahiro Toyoda, Toshiyuki Awaji, Nozomi Sugiura, Shuhei Masuda, Hiromichi Igarashi, Yuji Sasaki, Yoshihisa Hiyoshi, Yoichi Ishikawa, Takashi Mochizuki, Takashi T. Sakamoto, Hiroaki Tatebe, Yoshiki Komuro, Tatsuo Suzuki, Teruyuki Nishimura, Masato Mori, Yoshimitsu Chikamoto, Sayaka Yasunaka, Yukiko Imada, Miki Arai, Masahiro Watanabe, Hideo Shiogama, Toru Nozawa, Akira Hasegawa, Masayoshi Ishii, Masahide Kimoto, Impact of the assimilation of sea ice concentration data on an atmosphere-ocean-sea ice coupled simulation of the Arctic Ocean climate, Scientific Online Letters on the Atmosphere, 10.2151/sola.2011-010, 7, 1, 37-40, 2011.01, We have investigated the effects of assimilating sea ice concentration (SIC) data on a simulation of Arctic Ocean climate using an atmosphere-ocean-sea ice coupled model. Our results show that the normal overestimation of summertime SIC in the East Siberian Sea and the Beaufort Sea in simulations without sea-ice data input can be greatly reduced by assimilating seaice data and that this improvement is also evident in a following hindcast experiment for 3-4 years after the initialization of the assimilation. In the hindcast experiment, enhanced heat storage in both sea ice and in the ocean surface layer plays a central role in improving the accuracy of the sea ice distribution, particularly in summer. Our detailed investigation suggests that the ice-albedo feedback and the feedback associated with the atmospheric pressure pattern generated by the improved estimation of SIC work more effectively to retain the heat signal after initialization for a coupled atmosphere-ocean-sea ice system prediction. In addition, comparison with field observations confirms that the model fails to produce a realistic feedback loop, which is (presumably) due to inadequacies in both the ice-cloud feedback model and the feedback via the Beaufort Gyre circulation. Further development of coupled models is thus required to better define Arctic Ocean climate processes and to improve the accuracy of their predictions..
39. T. Toyoda, T. Awaji, S. Masuda, N. Sugiura, H. Igarashi, Takashi Mochizuki, Y. Ishikawa, Interannual variability of North Pacific eastern subtropical mode water formation in the 1990s derived from a 4-dimensional variational ocean data assimilation experiment, Dynamics of Atmospheres and Oceans, 10.1016/j.dynatmoce.2010.09.001, 51, 1-2, 1-25, 2011.01, The interannual variability of eastern subtropical mode water (ESTMW) formation in the North Pacific is examined using a new ocean dataset constructed by a 4-dimensional variational data assimilation experiment covering the decade of the 1990s. The volume of newly formed ESTMW varies due to interannual variability in the following three physical processes taking place in the surface layer: (1) convergence in the transport of surface saline water induced by Ekman flow in the vicinity of the formation region, (2) thermal stratification in the preconditioning phase in association with the insolation anomaly induced largely by low-level cloud coverage, and (3) wintertime surface cooling in the eastern subtropics. We find that, in addition to the surface forcing, the properties of both the ESTMW and the upper mixed-layer water are broadly controlled by the volume of the new ESTMW component, and that the variations in the upper mixed-layer water affect the properties of ESTMW formed in the following winter. Due to the combined effect of these processes, the ESTMW subducts down to subsurface layers with a wide range of σ
values lying between 24.8 and 25.4 and with significant interannual variation in water mass formation..
40. H. Shiogama, S. Emori, T. Mochizuki, S. Yasunaka, T. Yokohata, M. Ishii, T. Nozawa, M. Kimoto, Possible influence of volcanic activity on the decadal potential predictability of the natural variability in near-term climate predictions, Advances in Meteorology, 10.1155/2010/657318, 2010.06.
41. Takashi Mochizuki, Masayoshi Ishii, Masahide Kimoto, Yoshimitsu Chikamoto, Masahiro Watanabe, Toru Nozawa, Takashi T. Sakamoto, Hideo Shiogama, Toshiyuki Awaji, Nozomi Sugiura, Takahiro Toyoda, Sayaka Yasunaka, Hiroaki Tatebe, Masato Mori, Pacific decadal oscillation hindcasts relevant to near-term climate prediction, Proceedings of the National Academy of Sciences of the United States of America, 10.1073/pnas.0906531107, 107, 5, 1833-1837, 2010.02.
42. Takashi Mochizuki, Nozomi Sugiura, Toshiyuki Awaji, Takahiro Toyoda, Seasonal climate modeling over the Indian Ocean by employing a 4D-VAR coupled data assimilation approach, Journal of Geophysical Research: Oceans, 10.1029/2008JC005208, 114, 11, 2009.11, We carry out the first attempt to apply an adjoint method to a coupled general circulation model (CGCM) toward enhancing a skill in seasonal climate modeling. Focusing on 10-day mean errors of a CGCM output, we optimize the oceanic initial conditions together with the bulk adjustment factors by employing a four-dimensional variational data assimilation approach. We perform 9-month-long assimilation experiments independently every 6 months between January 1990 and March 2000. When using the optimized values for the initial conditions and the adjustment factors, a set of 9-month-long, 10-member ensemble simulation always displays realistic seasonal cycle and its interannual modulations over the tropical Indian Ocean (e.g., growing, mature, and decaying phases of the Indian Ocean Dipole Mode events). The optimized values of the bulk adjustment factors primarily reduce the model biases in climatological fields, while the optimization of the oceanic initial conditions largely contributes to a realistic representation of the interannual modulations of seasonal cycle. In the overlapped seasons (i.e., January-March and July-September), the ensemble mean states derived from two experiments show only slight differences in seasonal climate variations over most of the Indian Ocean. These results validate that our assimilation approach is generally effective for advancing a seasonal climate modeling and for obtaining a realistic analysis that is compatible between atmosphere and ocean..
43. T. Toyoda, S. Masuda, N. Sugiura, Takashi Mochizuki, H. Igarashi, M. Kamachi, Y. Ishikawa, T. Awaji, A possible role for unstable coupled waves affected by resonance between Kelvin waves and seasonal warming in the development of the strong 1997-1998 El Niño, Deep-Sea Research Part I: Oceanographic Research Papers, 10.1016/j.dsr.2008.12.002, 56, 4, 495-512, 2009.04, Time-varying air-sea coupled processes in the central to eastern equatorial Pacific associated with strong El Niño development during the 1997-1998 period are examined using a newly developed reanalysis dataset obtained from four-dimensional variational ocean-atmosphere coupled data assimilation experiments. The time series of this data field exhibits realistic features of El Niño evolution. Our analysis indicates that resonance between eastward-propagating oceanic downwelling Kelvin waves and the seasonal rise of sea-surface temperature (SST) in the central to eastern equatorial Pacific generates relatively persistent high SST conditions accompanied by a deeper thermocline and more relaxed easterly winds than usual. The surface condition resulting from the wave-seasonal SST resonance represents a preconditioned state that leads to an enhancement in incident downwelling Kelvin waves to levels sufficient to induce large-amplitude unstable coupled waves in the central to eastern equatorial region. Heat balance estimates using our reanalysis dataset suggest that the unstable coupled waves are categorized within the intermediate regime of coupled Kelvin and Rossby waves and have the potential to grow rapidly. We argue that the seasonal resonance and the unstable coupled waves should play crucial roles in the development of the largest historical El Niño event, which was recorded between late 1997 and early 1998..
44. Takashi Mochizuki, Toshiyuki Awaji, Nozomi Sugiura, Possible oceanic feedback in the extratropics in relation to the North Atlantic SST tripole, Geophysical Research Letters, 10.1029/2008GL036781, 36, 5, 2009.03, We analyze the results of 4-dimensional variational data assimilation experiments using a coupled general circulation model and identify signals from a possible extratropical oceanic feedback relating to the North Atlantic Sea Surface Temperature (SST) tripole. Examination of the optimized control variables (coupling parameters) and the resultant climate fields reveals that the model errors in the North Atlantic climate variations are very sensitive to the intensity of the extratropical air-sea thermal coupling. This results in the enhancement of the atmospheric responses to SST changes particularly around 40°N, 50°W, when the model errors are most effectively corrected. Since an adjoint approach enables us to detect the sensitivity to fluctuations in the model variables, our results suggest that this oceanic thermal feedback in the extratropics is a key physical process influencing the North Atlantic Oscillation and the associated North Atlantic SST tripole..
45. Nozomi Sugiura, Toshiyuki Awaji, Shuhei Masuda, Takashi Mochizuki, Takahiro Toyoda, Toru Miyama, Hiromichi Igarashi, Yoichi Ishikawa, Development of a four-dimensional variational coupled data assimilation system for enhanced analysis and prediction of seasonal to interannual climate variations, Journal of Geophysical Research: Oceans, 10.1029/2008JC004741, 113, 10, 2008.10, A four-dimensional variational (4D-VAR) data assimilation system using a coupled ocean-atmosphere global model has been successfully developed with the aim of better defining the dynamical states of the global climate on seasonal to interannual scales. The application of this system to state estimations of climate processes during the 1996-1998 period shows, in particular, that the representations of structures associated with several key events in the tropical Pacific and Indian Ocean sector (such as the El Niño, the Indian Ocean dipole, and the Asian summer monsoon) are significantly improved. This fact suggests that our 4D-VAR coupled data assimilation (CDA) approach has the potential to correct the initial location of the model climate attractor on the basis of observational data. In addition, the coupling parameters that control the air-sea exchange fluxes of mass, momentum, and heat become well adjusted. Such an initialization using the 4D-VAR CDA approach allows us to make a roughly 1.5-year lead time prediction of the 1997-1998 El Niño event. These results demonstrate that our 4D-VAR CDA system has the ability to enhance forecast potential for seasonal to interannual phenomena..
46. Takashi Mochizuki, Toshiyuki Awaji, Summertime evolution of decadal sea surface temperature anomalies in the midlatitude north pacific, Journal of Climate, 10.1175/2007JCLI1853.1, 21, 7, 1569-1588, 2008.04, To clarify the summertime evolution of decadal sea surface temperature (SST) anomalies and related physical processes in the midlatitudes of the North Pacific, numerical solutions of a three-dimensional bulk mixed layer model are analyzed, focusing on the contribution of the net shortwave radiative forcing at the sea surface. A quantitative heat budget analysis for the ocean mixed layer relating to late-1980s decadal SST change reveals that the decadal SST anomalies decay from late spring to early summer over the entire midlatitudes of the North Pacific. This quasi-seasonal decay of the decadal SST anomalies is controlled by an anomalous local thermal damping (i.e., anomalous surface heat fluxes). From midsummer to early autumn the anomalous net shortwave radiation flux associated with a meridional shift of the storm track acts to induce strong seasonal damping of the decadal SST anomaly in the northern Kuroshio-Oyashio Extension region. In contrast, in the north of the subtropical frontal region, the net shortwave radiation flux anomaly, which results from changes in low-level stratiform cloud cover, plays a major role in seasonally enhancing the decadal SST anomaly. Consequently, the SST anomalies formed by these radiative forcings cause significant variations in the local thermal damping rate at the sea surface over the period from late summer to early autumn..
47. Shang Ping Xie, Toru Miyama, Yuqing Wang, Haiming Xu, Simon P. de Szoeke, R. Justin O. Small, Kelvin J. Richards, Takashi Mochizuki, Toshiyuki Awaji, A regional ocean-atmosphere model for eastern Pacific climate
Toward reducing tropical biases, Journal of Climate, 10.1175/JCLI4080.1, 20, 8, 1504-1522, 2007.04, The tropical Pacific Ocean is a climatically important region, home to El Niño and the Southern Oscillation. The simulation of its climate remains a challenge for global coupled ocean-atmosphere models, which suffer large biases especially in reproducing the observed meridional asymmetry across the equator in sea surface temperature (SST) and rainfall. A basin ocean general circulation model is coupled with a full-physics regional atmospheric model to study eastern Pacific climate processes. The regional ocean atmosphere model (ROAM) reproduces salient features of eastern Pacific climate, including a northward displaced intertropical convergence zone (ITCZ) collocated with a zonal band of high SST, a low-cloud deck in the southeastern tropical Pacific, the equatorial cold tongue, and its annual cycle. The simulated low cloud deck experiences significant seasonal variations in vertical structure and cloudiness; cloud becomes decoupled and separated from the surface mixed layer by a stable layer in March when the ocean warms up, leading to a reduction in cloudiness. The interaction of low cloud and SST is an important internal feedback for the climatic asymmetry between the Northern and Southern Hemispheres. In an experiment where the cloud radiative effect is turned off, this climatic asymmetry weakens substantially, with the ITCZ migrating back and forth across the equator following the sun. In another experiment where tropical North Atlantic SST is lowered by 2°C - say, in response to a slow-down of the Atlantic thermohaline circulation as during the Younger Dryas - the equatorial Pacific SST decreases by up to 3°C in January-April but changes much less in other seasons, resulting in a weakened equatorial annual cycle. The relatively high resolution (0.5°) of the ROAM enables it to capture mesoscale features, such as tropical instability waves, Central American gap winds, and a thermocline dome off Costa Rica. The implications for tropical biases and paleoclimate research are discussed..
48. Takashi Mochizuki, Toru Miyama, Toshiyuki Awaji, A simple diagnostic calculation of marine stratocumulus cloud cover for use in general circulation models, Journal of Geophysical Research Atmospheres, 10.1029/2006JD007223, 112, 6, 2007.03, An improved diagnostic calculation for determining the marine stratocumulus (SCu) cloud cover has been implemented for atmospheric and coupled general circulation models (GCMs). The approach aims to improve the simulated climatological features of the lower troposphere and to reduce warm sea surface temperature (SST) biases that develop along western continental coasts in the subtropical regions of coupled GCMs. In the new diagnostic calculation introduced in the present study, the SCu cloud cover was linearly regressed to atmospheric stability, and the temporal and spatial distributions of the regression coefficients were estimated beforehand using observational data sets. The upward transport of heat, moisture and momentum in subcloud layers accompanying the SCu was also simulated by controlling the vertical diffusion coefficients. Using the new calculation, the SCu cloud cover in an atmospheric GCM become more representative in both spatial and seasonal variations. In addition, the simulation of related atmospheric structures in the lower troposphere is considerably improved. Furthermore, when the new calculation is applied to a coupled GCM, SST values to the west of continents in subtropical areas display weakened warm biases and more realistic seasonal cycles resulting from the modification of the downward shortwave radiation flux at the sea surface. The new calculation introduces both local and large-scale improvements in model climatology over low-latitude and midlatitude regions. In the eastern Pacific, for example, a shallow meridional circulation across the equator is excited, and the strength and location of the intertropical convergence zone and the seasonal cycle of equatorial SST become more realistic..
49. Takashi Mochizuki, Hiromichi Igarashi, Nozomi Sugiura, Shuhei Masuda, Nobuhiro Ishida, Toshiyuki Awaji, Improved coupled GCM climatologies for summer monsoon onset studies over Southeast Asia, Geophysical Research Letters, 10.1029/2006GL027861, 34, 1, 2007.01, To enhance accurate estimates of Asian monsoon variability by a coupled general circulation model (GCM), the bulk adjustment factors that control latent heat, sensible heat and momentum fluxes are optimized using a 4-dimensional variational data assimilation method. When using the optimized values, a coupled GCM is better able to define the summer monsoon features over Southeast Asia. In particular, the early, rapid onset is realistically simulated around the Indochina Peninsula, which is a key region for the initial stage of the Asian summer monsoon development. The spatial patterns of precipitation rate, wind velocity, and sea surface temperature are successfully reproduced. The optimized values of the bulk adjustment factors for latent heat flux become significantly correlated with the strength of the subgrid-scale disturbances primarily associated with energetic deep convective activities in the tropics, which is one of the major sources of model biases in commonly-used coarse resolution models..
50. Takashi Mochizuki, Hideji Kida, Seasonality of decadal sea surface temperature anomalies in the northwestern Pacific, Journal of Climate, 10.1175/JCLI3807.1, 19, 12, 2953-2968, 2006.06, The seasonality of the decadal sea surface temperature (SST) anomalies and the related physical processes in the northwestern Pacific were investigated using a three-dimensional bulk mixed layer model. In the Kuroshio-Oyashio Extension (KOE) region, the strongest decadal SST anomaly was observed during December-February, while that of the central North Pacific occurred during February-April. From an examination of the seasonal heat budget of the ocean mixed layer, it was revealed that the seasonal-scale enhancement of the decadal SST anomaly in the KOE region was controlled by horizontal Ekman temperature transport in early winter and by vertical entrainment in autumn. The temperature transport by the geostrophic current made only a slight contribution to the seasonal variation of the decadal SST anomaly, despite controlling the upper-ocean thermal conditions on decadal time scales through the slow Rossby wave adjustment to the wind stress curl. When averaging over the entire KOE region, the contribution from the net sea surface heat flux was also no longer significantly detected. By examining the horizontal distributions of the local thermal damping rate, however, it was concluded that the wintertime decadal SST anomaly in the eastern KOE region was rather damped by the net sea surface heat flux. It was due to the fact that the anomalous local thermal damping of the SST anomaly resulting from the vertical entrainment in autumn was considerably strong enough to suppress the anomalous local atmospheric thermal forcing that acted to enhance the decadal SST anomaly..
51. Takashi Mochizuki, Hideji Kida, Maintenance of decadal SST anomalies in the midlatitude North Pacific, Journal of the Meteorological Society of Japan, 10.2151/jmsj.81.477, 81, 3, 477-491, 2003.06, Mechanisms that maintain decadal sea surface temperature (SST) anomalies in the midlatitudes North Pacific are investigated using observational data. Focussing on the seasonality of decadal SST anomalies, individual heat budget analyses were conducted for the ocean mixed layer in a southern region (25°N-35°N, 175°E-145°W , and a northern region (39°N-49°N, 165°E-155°W) of the North Pacific. It was revealed that the decadal SST anomaly in the southern region, which was pronounced in winter, was significantly maintained by meridional Ekman temperature advection that occurred during November-January. On the other hand, the decadal SST anomaly in the northern region, which was observed in almost all months, was maintained by the sum of the effects of sensible and latent heat flux, and the net long wave radiation flux at the sea surface, and the meridional Ekman temperature transport during the period of October-December. In the Kuroshio extension region, which overlaps the southwest portion of the northern region, the anomalous temperature transport by entrainment in the seasonal thermocline was found to be very important for the maintenance of decadal SST anomaly..