Kyushu University Academic Staff Educational and Research Activities Database
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Hiroki Tokinaga Last modified date:2022.06.09



Graduate School


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Homepage
https://kyushu-u.pure.elsevier.com/en/persons/hiroki-tokinaga
 Reseacher Profiling Tool Kyushu University Pure
Academic Degree
Ph.D (Environmental Earth Science)
Country of degree conferring institution (Overseas)
No
Field of Specialization
Climate Dynamics
ORCID(Open Researcher and Contributor ID)
https://orcid.org/0000-0002-2734-1820
Total Priod of education and research career in the foreign country
07years06months
Outline Activities
My research interests include climate variability and change, with a particular focus on basin-scale ocean-atmosphere interactions over the tropical oceans. We aim to clarify physical mechanisms for and improve future predictions of climate phenomena by synthesizing ocean and atmospheric observations and climate model experiments.
Research
Research Interests
  • Tropical Basin Interaction
    keyword : climate variability, ocean-atmosphere interaction, atmospheric teleconnection, climate change
    2020.01.
  • Reconstruction of global marine surface wind dataset from ship observations
    keyword : Marine surface wind, ship observations, climate change
    2010.09.
  • Influence of persistent El Niño/Southern Oscillation events on the Atlantic Niño
    keyword : El Niño/Southern Oscillation, Atlantic Niño, atmospheric teleconnection
    2018.04.
  • Arctic warming and interdecadal oscillation over the Pacific and Atlantic
    keyword : Arctic amplification, Interdecadal Pacific Oscillation, Atlantic Multidecadal Oscillation
    2015.04.
  • Mechanisms for climate change pattern formation over tropical oceans
    keyword : Climate change, ocean-atmosphere interaction, climate models
    2009.10.
  • Ocean-atmosphere interaction near the mid-latitude sea surface temperature fronts
    keyword : Satellite and ship observations, radiosonde, surface heat flux, atmospheric boundary layer, high-resolution ocean-atmosphere coupled models
    2003.04.
Academic Activities
Books
1. Ingo Richter, Hiroki Tokinaga, The Atlantic zonal mode: dynamics, thermodynamics, and teleconnections: Tropical and Extra-tropical Air-Sea Interactions, S.K.Behera, Ed., Elsevier, in press.
Reports
1. Hiroki Tokinaga, Shang-Ping Xie, Fumiaki Kobashi, Youichi Tanimoto, Local and remote influences of the Kuroshio Extension on the atmosphere, U. S. CLIVAR Variations, 2009.12.
Papers
1. Ingo Richter, Hiroki Tokinaga, Yuko M. Okumura, The extraordinary equatorial Atlantic warming in late 2019, Geophysical Research Letters, 10.1029/2021GL095918, 2022.02, Sea-surface temperatures (SSTs) in the eastern equatorial Atlantic are subject to variability on interannual timescales but during the last 20 years, this variability has shown comparatively little activity. In late 2019, however, the warmest event in the satellite observation period developed. Analysis suggests that zonal wind stress anomalies in the western equatorial Atlantic contributed to the development of the warm SST anomalies. Furthermore, wind stress curl anomalies north of the equator generated downwelling Rossby waves that propagated to the western boundary and were reflected into downwelling Kelvin waves that helped to precondition the event. Neither the contemporaneous positive Indian Ocean Dipole nor the El Niño Modoki appears to have contributed substantially to the Atlantic warming, though some uncertainty remains. Based on large-scale multidecadal variability patterns, a return to enhanced variability is not imminent but careful monitoring will be important..
2. Ingo Richter, Hiroki Tokinaga, An overview of the performance of CMIP6 models in the tropical Atlantic: mean state, variability, and remote impacts, Climate Dynamics, 10.1007/s00382-020-05409-w, 55, 2579-2601, 2020.08, General circulation models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) are examined with respect to their ability to simulate the mean state and variability of the tropical Atlantic and its linkage to the tropical Pacific. While, on average, mean state biases have improved little, relative to the previous intercomparison (CMIP5), there are now a few models with very small biases. In particular the equatorial Atlantic warm SST and westerly wind biases are mostly eliminated in these models. Furthermore, interannual variability in the equatorial and subtropical Atlantic is quite realistic in a number of CMIP6 models, which suggests that they should be useful tools for understanding and predicting variability patterns. The evolution of equatorial Atlantic biases follows the same pattern as in previous model generations, with westerly wind biases during boreal spring preceding warm sea-surface temperature (SST) biases in the east during boreal summer. A substantial portion of the westerly wind bias exists already in atmosphere-only simulations forced with observed SST, suggesting an atmospheric origin. While variability is relatively realistic in many models, SSTs seem less responsive to wind forcing than observed, both on the equator and in the subtropics, possibly due to an excessively deep mixed layer originating in the oceanic component. Thus models with realistic SST amplitude tend to have excessive wind amplitude. The models with the smallest mean state biases all have relatively high resolution but there are also a few low-resolution models that perform similarly well, indicating that resolution is not the only way toward reducing tropical Atlantic biases. The results also show a relatively weak link between mean state biases and the quality of the simulated variability. The linkage to the tropical Pacific shows a wide range of behaviors across models, indicating the need for further model improvement..
3. Hiroki Tokinaga, Ingo Richter, Yu Kosaka, ENSO influence on the Atlantic Niño, revisited: Multi-year versus single-year ENSO events, Journal of Climate, 10.1175/JCLI-D-18-0683.1, 32, 14, 4585-4600, 2019.06, The influence of El Niño-Southern Oscillation (ENSO) on the Atlantic Niño over the past 113 years is investigated by comparing multi-year and single-year ENSO events. Multi-year ENSO events sustain an anomalous zonal gradient of sea surface temperature (SST) in the equatorial western to central Pacific even during boreal spring and summer. This SST gradient is coupled with an anomalous Walker circulation and atmospheric deep convection through the Bjerknes feedback. During multi-year La Niñas, for example, a strengthened Pacific Walker circulation extends into the tropical Atlantic in boreal spring, a season when both the Pacific and Atlantic intertropical convergence zones become more symmetric about the equator. As a result, surface westerly wind anomalies appear over the equatorial Atlantic, triggering an Atlantic Niño. By contrast, such a teleconnection is not found in the spring following the peak of single-year ENSO events. A Pacific pacemaker model experiment reproduces the observed atmospheric response and its impact on the Atlantic Niño, further supporting the importance of prolonged ENSO forcing. The contrasting influence of multi-year and single-year events explains the fragile relationship between ENSO and the Atlantic Niño. An empirical orthogonal function (EOF) analysis shows that the leading EOF mode (EOF-1) for the spring tropical western to central Pacific SST anomalies captures the characteristics of multi-year ENSO events. EOF-1 is highly correlated with the summer Atlantic Niño over the past 113 years while the Niño-3 SST is not. These correlations indicate that ocean-atmosphere coupling in the equatorial western to central Pacific plays a major role in shaping ENSO teleconnections in boreal spring..
Works, Software and Database
1.
[URL].
Presentations
1. Hiroki Tokinaga, Decadal variability of the Benguela Nino/Nina, JpGU-AGU Joint Meeting 2020, 2020.07.
2. Hiroki Tokinaga, Shang-Ping Xie, Hitoshi Mukougawa, Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability, 9th International Workshop on Tropical-subtropical Weather, Climate and Oceans, 2017.11.
3. Hiroki Tokinaga, Patterns and influence of tropical ocean warming: Observations and simulations, 2nd JSPS Core-to-core International Workshop, 2016.08.
4. Hiroki Tokinaga, Shang-Ping Xie, Axel Timmermann, Shayne McGregor, Tomomichi Ogata, Hisayuki Kubota, Yuko M. Okumura, Regional patterns of tropical Indo-Pacific climate change: Evidence of the Walker Circulation weakening, AGU Fall Meeting, 2012.12.
5. Hiroki Tokinaga, Shang-Ping Xie, Clara Deser, Yu Kosaka, Axel Timmermann, Shayne McGregor, Tomomichi Ogata, Hisayuki Kubota, Yuko M. Okumura, Observed and simulated patterns of tropical Indo-Pacific climate change over the past six decades: Evidence of the Walker circulation slowdown, The 3rd International Conference on Earth System Modeling, 2012.09.
6. Hiroki Tokinaga, Shang-Ping Xie, A long, consistent surface wind dataset for climate change analysis: Application over the tropical Indo-Pacific, WCRP Open Science Conference, 2011.10.
7. Hiroki Tokinaga, Shang-Ping Xie, Shoshiro Minobe, Atmospheric effects of the Gulf Stream and Kuroshio Extension, AGU Fall Meeting, 2008.12.
Membership in Academic Society
  • The Oceanographic Society of Japan
  • Japan Geoscience Union
  • The Meteorological Society of Japan
  • American Meteorological Society
  • American Geophysical Union
Educational
Educational Activities
Descriptive Marine Physics/Earth System Science and Technology/Interdisciplinary Graduate School of Engineering Sciences