気候システムセミナー

日時：金曜日 13:30-15:00
場所：東京大学柏キャンパス 総合研究棟270室
（＊変更の場合もありますので、詳細は下記の予定をご確認ください）

今後の予定

• Title: BWJ指数解析：準解析的ENSOの診断法
• Time: 15:30 - 17:00 on January 29, 2026.
• Place: General Research Bldg. 2F room 270
• Abstract: 気候モデルにおける ENSO の表現には多くの不確実性が存在し、その要因を切り分けて理解し改善することは課題である。ENSO の診断には多様なアプローチがあるが、Recharge Oscillator（RO）理論に基づき導出された Bjerknes–Wyrtki–Jin（BWJ）指数解析は平均場やフィードバックの強度まで分離することができ幅広く利用されている。しかし領域依存性や方程式体系に起因する不確実性が残り、依然改善の余地がある。 本研究は、海洋表層の収支式から RO方程式を準解析的に導出し、それに基づく BWJ 指数導出の枠組みを提示することを目的とする。提案する更新フレームワークは特定の領域設定に依存せず適用可能であり、ENSO の空間パターンの違いを許容した上で、その力学過程の理解と要因分解に資する（予定である）。

• Title: Future mesoscale horizontal stirring in polar oceans intensified by sea ice decline
• Time: 15:30 - 17:00 on January 23, 2026.
• Place: General Research Bldg. 2F room 270
• Abstract: Mesoscale horizontal stirring (MHS) is ubiquitous in the oceans, influencing heat and carbon transport, phytoplankton blooms and fish larvae dispersal. The current generation of Earth system models lacks sufficient resolution to properly resolve MHS-relevant small-scale phenomena, such as oceanic mesoscale eddies, leaving it largely unknown how MHS will change in response to greenhouse warming. Here we determine how CO2 doubling and quadrupling will change the surface MHS statistics in Community Earth System Model simulations with 1/10-degree ocean resolution. MHS is analysed using the finite-size Lyapunov exponent, a Lagrangian diagnostic that measures the separation of close trajectories. Projected increases in MHS are expected in the Arctic Ocean and coastal Antarctic regions, driven by enhanced time-mean ocean flow and turbulence which predominantly result from sea ice reduction. The enhanced horizontal stirring in polar oceans implies substantial yet uncertain consequences for tracer transport, nutrient supply and ecosystems under higher CO2 conditions.

• 場所: 総合研究棟270室

• Title: Multi-Year La Nia Events: From Ocean Dynamics to Hydrological Impact
• Time: 15:30 - 17:00 on December 10, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: Multi-year La Nia events challenge our understanding of El Nio–Southern Oscillation (ENSO) dynamics and reveal unexpected complexities in the climate system. ENSO reflects the coupled evolution of sea surface temperature in the eastern tropical Pacific and warm-water volume in the equatorial Pacific, traditionally described by the recharge-oscillator framework. La Nia can occasionally persist for two or even three consecutive years. Such multi-year events typically follow strong El Nio conditions that deplete warm-water volume and require several years for the equatorial Pacific to recharge. However, the recent 2020–22 triple-dip La Nia did not follow this pathway, raising a fundamental question about what triggered this event.
  This seminar will introduce the distinctive characteristics of the recent triple-dip La Nia by contrasting it with the classic recharge-oscillator paradigm. Our analyses indicate that remote forcing from the Indian Ocean Dipole and tropical Atlantic warming played central roles in initiating this event. Targeted partial-ocean data assimilation experiments using CESM with assimilation confined to the Atlantic and Indian Oceans further support this inter-basin triggering mechanism. I will also discuss the downstream hydroclimate impacts of multi-year La Nia events in the western United States, focusing on their influence on seasonal drought evolution and their potential to enhance predictive capability.

• Title: Cloud thermodynamic phase inferred from muti-angle observation of SWIR and polarization
• Time: 13:30 - 15:00 on November 21, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: Cloud thermodynamic phase (ice, liquid, supercooled water) discrimination have critical impacts on the Earth’s energy budget and hydrological cycle. Also, cloud phase classification is an important first step for cloud optical and microphysical parameter retrievals. There are several approaches successfully applied to the passive sensor (like MODIS, POLDER and SGLI), including thermal infrared measurements, shortwave infrared and visible measurements and polarization measurement. The absorption of ice and water cloud in shortwave infrared (SWIR) channel is of obvious difference, and the water vapor absorption channel in SWIR is sensitive of cloud height, while polarization characterization has strong dependence on cloud particle shapes. In this study, we combine the three different observations for inferring cloud phase into a single algorithm, using only PMAI (Polarization Muti-Angle Imager) data onboard FengYun rainfall satellite, which have three muti-angle SWIR polarization channel. Different polarization behavior from three SWIR channels will be present for ice, liquid, supercooled water and mixed clouds. To evaluate the performance of the algorithm, extensive granule-level comparisons have been conducted against passive imagers and active sensors (like EarthCARE and ACDL). This result data is expected to be useful for cloud assimilation and modeling efforts while providing more insight into the global cloud properties derived from satellite data.

• Title: Climate change is really weather change - why might you care?
• Time: 10:00 - 11:30 on November 12, 2025.
• Place: General Research Bldg. 2F room 270（＊気候コロキウムと合同開催）
• Abstract: "A good decision is based on knowledge, and not on numbers" - Plato
  Our climate is changing. The Earth is getting warmer. We are responsible. These statements are now unequivocal and we have sufficient quantitative information to set global mitigation targets. However, the impacts of the changing climate are felt locally and the implementation of mitigation actions and adaptation efforts to protect ourselves from unavoidable change all occur at local to regional scales. Whilst projections of future climate are based on complex climate models underpinned by physical laws, their results are usually assessed using simple statistical frameworks, such as averages, variances and extreme value statistics for near-surface variables, in other words - numbers.
  We argue, that what truly matters to local and regional change is not the change in the broad features of the climate, but it is how the weather is changing. We show that every high-impact climate event is a weather event. We also highlight the important role that weather plays as a resource and how a NetZero society will be the most weather-dependent in centuries. Reframing climate change as weather change for both science and decision making implies the need for new science and new tool, including very high-resolution models. We will provide examples from the research of 21st Century Weather to demonstrate how we intend to advance our understanding of weather change, which will ultimately provide what we need most - the knowledge to underpin the numbers.

• Title: Some aspects of the air-sea interface and the ocean CO2 sink
• Time: 13:30 - 15:00 on October 28, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract:In this talk, I will present findings on two aspects relevant for the global ocean CO2 sink. (i) The first concerns a common bias in all the data-based products estimates that participate to the Global Carbon Budget exercise. This bias originates from neglecting submonthly variations of atmospheric pressure; (ii) The second shows the first results on the effect of biogenic surfactants on the ocean surface brightness temperature on the global scale. These results suggest that surfactants should be the subject of further research as they can impact CO2 air-sea fluxes in coastal productive regions usually targeted for mCDR.
  
  (i) Current estimates of the global ocean carbon sink based on measurements of CO2 fugacity are inconsistent with those obtained from global ocean biogeochemistry models. Here we investigate how this gap might be partially closed by more fully accounting for submonthly variability in observation-based estimates. While these estimates compute the air-sea CO2 flux based on hourly wind speed, other variables have only monthly resolution. Thus they neglect some high-frequency variability from short-term events such as storms. To evaluate this error, we compare fluxes at different temporal resolutions between 2009 and 2018. We find that accounting for hourly variations in atmospheric pressure and daily variations in sea surface temperature decreases the global carbon uptake estimate by 5% (0.12 Pg C yr-1) which is driven by the submonthly covariance between wind speed and atmospheric pressure, particularly in the southern extratropics. This represents 25% of the average gap between observation-based and model estimates.
  
  (ii) We show that the ocean interface cool skin effect is sensitive to the biologic activity reflected by the chlorophyll-a concentration (Chla) in the upper ocean. For this, we used sea surface skin temperatures Tskin retrieved from spectra recorded by the Infrared Atmospheric Sounder Interferometer (IASI) and collocated measurements of drifter bulk temperature Tbulk and Chlorophyll-a concentrations from a daily Copernicus satellite product. The results demonstrate that |ΔT_obs, with ΔT_obs= Tskin - Tbulk <0, increases with Chla, particularly when the surface wind is weak. This finding is attributed to the hydrodynamic damping of ocean near surface turbulence by biogenic surfactant that leads to an increase of the cool skin thickness. Parametric formulations of the cool skin temperature difference and thickness depending on both wind speed and Chla are proposed. This enables to assess the global impact of biogenic surfactant on interfacial temperature that is mostly a coastal and Arctic phenomenon.

• Title: Paradigm Shift from Human Weather Forecaster to AI Weather Forecaster
• Time: 10:30 - 12:00 on October 24, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: People have attempted to predict the weather informally for thousands of years. Ancient weather forecasting methods usually relied on observed patterns of events, also termed pattern recognition. In about 350 BC, Aristotle described weather patterns in 'Meteorologica'
  In 1854, Le Verrier, he produced the first weather chart using a network of meteorological observations and the telegraph, playing a key role in advancing the transition from the era of meteorological instruments to the era modern weather forecasting.
  In 1922, English scientist Lewis Fry Richardson published "Weather Prediction By Numerical Process" and Practical use of numerical weather prediction began in 1955.
  
  Global big technology companies and NMHS (National Meteorological and Hydrological Service) agencies are rapidly developing artificial intelligence (AI) - based forecasting models.
  The Korea Meteorological Administration (KMA) is building an operational AI forecasting system by monitoring international advances and strengthening collaboration with universities and research institutes. Three AI models have been installed and are currently used alongside the existing global numerical model (KIM, UM, ECMWF), with emphasis on short-term precipitation prediction.
  The Typhoon Research Center, Jeju National University and KMA evaluated five AI models and ECMWF IFS using eight typhoons that affected Korean Peninsula after 2020. Results showed that Google’s GraphCast provided the most accurate 7-day track forecasts, while model ECMWF IFS most accurate of intensity. However, AI models generally underestimated tropical cyclone intensity, indicating a need for improvement.
  Although 1st and 2nd Geostationary Satellite images, KMA have enhanced intensity predictions, further progress remains necessary.
  
  Future work will focus on expanding verification cases, improving intensity forecasts, and extending AI applications to seasonal prediction.
  The era of AI-based forecasting has arrived.

• Title: Role of Atmosphere-Sea Ice-Ocean interactions in millennial-scale glacial climate variability
  「数千年スケール氷期気候変動における大気-海氷-海洋相互作用の役割」
• Time: 9:45 - 11:45 on October 20, 2025.
• Place: General Research Bldg. 2F room 270

• Title: 全球亜鉛循環を支配する生物地球化学過程に関する研究
• Time: 13:30 - 15:30 on October 20, 2025.
• Place: General Research Bldg. 2F room 270

• Title: 欧州/GRASPの地上・衛星エアロゾルリモートセンシングの現状
• Time: 13:30 - 15:00 on August 8, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: 現在欧州では3MIをはじめとする多くの衛星打ち上げが計画されており、それらの衛星の中にはエアロゾルの現業プロダクトの導出にGRASPアルゴリズムが利用されている。近年は小型多波長・多偏光衛星の打ち上げとそれを用いたエアロゾル・地表面パラメータの導出も試みられている。その他、二酸化炭素やメタン等の地球温暖化ガスの同時導出や、熱赤外線リモートセンシングへの利用も進んでいる。これらのGRASPの開発状況と将来展望について報告する。

• Title: A Lagrangian view of deep convective clouds
• Time: 10:30 - 12:00 on July 29, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: Cumulus clouds are systems of considerable importance. They are key components of large-scale systems, such as the Inter-Tropical Convergence Zone or the Walker Circulation, which play a significant role in the Earth’s climate; also, certain forms of deep convection are known to produce severe weather that can pose considerable threat to human life. In spite of its relevance, there are still many aspects of cumulus convection that remain to be fully understood. In this talk, I will focus on one such aspect, an example of gravity currents known as cold pools. These convective features are generated by evaporatively-cooled downdraft air which, after having sunk to the surface, expands out radially. After discussing the importance of cold pools in deep convective dynamics, I will illustrate how a Lagrangian perspective can efficiently be used to shed light on many aspects characterizing these objects. In particular, I will show how Lagrangian particles in a numerical model can help identify and track cold pools in a simulated precipitating system. Using this tracking method, I will then present results regarding key properties of the downdrafts generating cold pools, the origin of the moisture anomalies often observed around propagating cold pools, and the mechanisms through which cold pools can trigger new convective cells. Finally, I will present some recent results regarding cold pool collisions and how these impact the life cycle of cold pools themselves.

• Title: 移動性傾圧擾乱に着目した南半球傾圧環状モード変動の構造・時間発展の再検討
• Time: 10:00 - 11:30 on July 9, 2025.
• Place: General Research Bldg. 2F room 270 （＊気候コロキウムと合同開催）
• Abstract: 中高緯度対流圏で繰り返し発達する高低気圧渦は、周辺地域の日々の天気変化をもたらすだけでなく、熱や運動量、水蒸気等の輸送を通じて、全球規模の気候系の維持にも重要な役割を果たす。傾圧環状モード変動（baroclinic annular mode; BAM）は、中高緯度対流圏における渦運動エネルギーの第1EOFとして両半球で各々定義され、その半球規模での強弱を表す卓越変動モードである。BAMは、渦運動エネルギーや渦による極向き熱輸送、また、降水量の半球規模での強弱を明瞭に伴い、降水を伴う傾圧擾乱活動の強弱を反映すると考えられる。 BAMは当初、循環の東西非対称成分としての「渦」に基づき定義された。しかし、この従来手法では、力学特性が大きく異なることが知られている周期約1週間以下の移動性傾圧擾乱と、より長周期の準停滞性擾乱の寄与が区別されておらず、これがBAMの実態やメカニズムに関する解釈を困難にする可能性がある。そこで本研究では、時間フィルタを用いて短周期・長周期の擾乱成分を区別した上で、南半球で見られるBAMの空間構造と時間発展について再検討を行った。 本発表では、短周期の傾圧擾乱の寄与が従来より知られるBAMの重要な特徴において本質的に重要であること、より長周期の擾乱の寄与はこれらとは異なる特徴と示すことを指摘した上で、短周期擾乱の寄与に着目してBAMの力学特性について再検討を行った結果について紹介する。

• Title: Development of Energy Balance Climatology
• Time: 13:40 - 15:10 on June 24, 2025.
• Place: General Research Bldg. 3F room 320
• Abstract: 気候の成因を理解するに熱収支は最も端的な方法である。熱収支気候学の発展過程を概観しその成功と失敗を分析し、それが現在どこに位置し、将来の展開はどうであるかを考える。

• Title: Tropical to extratropical interactions using a hierarchy of model experiments
• Time: 13:30 - 15:00 on June 19, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: Tropical variability has long been identified as having an important influence on climate variability and change in the extratropical regions. Heating from tropical convection can generate stationary Rossby waves that propagate polewards and eastwards towards the poles, influencing temperature and rainfall patterns along the way. Recent studies have also highlighted the reverse - an influence of the polar regions on changes further north, for example, the stratospheric weakening of the Southern Hemisphere polar vortex that contributed to the prolonged drought and catastrophic fires in Australia in the spring and summer of 2019. In my talk, I will discuss some recent studies to understand these tropical to extratropical interactions using a hierarchy of global model experiments. I will also introduce the work we are undertaking towards developing kilometre scale global and regional versions of the ACCESS model in the ARC Centre of Excellence for 21^st Century Weather.

• Title: AMOC弱化に伴う北大西洋での塩分大変動
• Time: 15:30 - 17:00 on June 13, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: 北大西洋は高密度の水塊を形成することで大西洋深層循環（AMOC）を駆動する重要な海域である。様々な証拠から地球温暖化によりAMOCが弱化することで全球で急激な気候変化が引き起こされることが懸念されているものの、気候変動への影響に関する研究はいまだ少ない。本研究では気候モデルを用いて、北大西洋における海洋塩分の極端現象であるGreat Salinity Anomaly（GSA）がAMOC弱化時に急激に振幅が増加することを示す。塩分収支解析から海洋内部の力学によりGSAが伝播、強化されており、特にAMOC弱化による北大西洋海流の弱化と塩分の空間分布の変化で特徴づけられることが分かった。また一例として気候緩和シナリオにおける塩分変動の変化を示し、例え二酸化炭素濃度を緩和した場合でも振幅増加が共通してみられることを示す。さらにこの塩分変動に関連する海面高度変動の強化は北大西洋沿岸地域に対して高潮のリスクを高める可能性がある。

• Title: Perspectives on High-Temporal-Resolution Surface Solar Radiation Observations
• Time: 10:00 - 11:30 on June 11, 2025.
• Place: General Research Bldg. 2F room 270 （＊気候コロキウムと合同開催）
• Abstract: Surface observations remain the only direct measurements for understanding the surface energy budget. Coordinated surface solar radiation observations began during the International Geophysical Year (IGY) in the late 1950s, initiated by the World Meteorological Organization (WMO). These long-term observational records have provided valuable insights into the phenomena of global dimming and brightening, the radiative effects of clouds and aerosols, and the implications for solar energy and agricultural production. Since the 1990s, advancements in automated instrumentation have enabled measurements at hourly and sub-hourly intervals. These high-temporal-resolution observations make it possible to investigate the diurnal evolution of surface solar radiation and the associated environmental processes, to evaluate the performance of mainstream gridded datasets in estimating hourly surface solar radiation, and to contribute a more comprehensive understanding of key climatological parameters in the field of atmospheric radiation, which will be the central focus of this presentation.

• Title: Tropical Pacific Sea Surface Temperature Patterns and the El Nio Southern Oscillation under Climate Change
• Time: 10:30 - 12:00 on June 2, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: This lecture will discuss the impact of climate change in the tropical Pacific ocean-atmosphere system, and the wider global impacts of these changes. Topics covered will include the mean-state pattern of sea surface temperature (SST) change and the discrepancy between observations and models, physical processes responsible for uncertainties in future tropical Pacific SST patterns, and the impact of those mean-state SST pattern changes on rainfall in N. and S. America. The lecture will also discuss changes in the variability of the El Nio Southern Oscillation (ENSO) including the time of emergence of changes in the mean state and ENSO, the time of emergence of changes in the Walker Circulation, and changes in ENSO teleconnection patterns in North America and Europe.

• Title: The impact of climate change on the global economy
• Time: 15:00 - 16:30 on May 19, 2025.
• Place: General Research Bldg. 2F room 270
• Abstract: This seminar delves into the complex interplay between climate change and socioeconomic development, emphasizing the reciprocal effects of climate patterns on economic growth. Utilizing research from the Climate Impacts and Adaptation (CIA) group, we will analyze the application of Earth System Models and Integrated Assessment Models to evaluate climate impacts on global and regional economies. A key focus will be on internal climate variability, which complicates the attribution of economic damages to climate change due to its inherent uncertainties. The seminar will address the limitations of current climate models in capturing extreme weather events and discuss advancements in global kilometer-scale models that enhance the representation of climate variability. Additionally, we will explore the development of comprehensive Integrated Assessment Models (IAMs) that illustrate interactions between human and natural systems, advocating for a two-way coupling approach to better understand climate change impacts on human systems. This approach is vital for developing effective adaptation strategies and exploring potential climate futures. By integrating cutting-edge climate science with economic analysis, this seminar aims to provide critical insights for local climate change adaptation planning and inform global policy-making, adaptation, and mitigation strategies.

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