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

• 場所: 270室

• Title:「氷期における大西洋子午面循環の多重解構造に関する研究」
• Time: 15:00 - 17:00 on Oct. 10, 2023.
• Place: General Research Bldg. 2F room 270とZoomでのハイブリット開催

• Title:「赤道域における季節内大気海洋相互作用に関する研究」
• Time: 15:00 - 17:00 on Sep. 15, 2023.
• Place: General Research Bldg. 2F room 270とZoomでのハイブリット開催
• Abstract: 赤道域の季節内スケールの大気海洋結合は大気の湿潤対流を理解する上で重要である。また、結合モデルが高解像度化されつつあり、湿潤対流と海洋の相互作用の表現を評価する手法が必要とされている。そこで本研究では90日ハイパスフィルタ(HPF)を適用した海面水温（SST）と可降水量(CWV)の相空間内で時間発展を合成し、大気主導の効果と海洋主導の効果を区別する手法を提案する。さらに提案手法をモデルシミュレーション結果に対して適用し観測との比較を行う。 再解析データ等を用いてSST-CWV相空間内の時間発展を合成解析したところ、西太平洋では反時計回り（SSTがCWVに先行する）に対して、東太平洋では時計回り（CWVがSSTに先行する）であった。この回転方向の違いは、SSTの時間変化に寄与する要因の違いと関連しており、西太平洋では雲を介した放射の地表面への入射が、東太平洋では東西風に伴う赤道湧昇が主にSSTの変化に寄与している。詳細な時空間分布を確認したところ、時計回りの時間発展レジームはENSOに伴う冷舌域に対応することがわかった。SSTとCWVの変動の時間スケールについては、90日HPF成分のうち短周期(10日HPF)成分の寄与が大きいことがわかった。 この解析手法を大気海洋結合モデルNICOCOのシミュレーション結果に適用したところ、時間発展の方向は西太平洋では反時計回りと観測と一致したが、東太平洋では観測とは異なり反時計回りであった。この手法がモデルの大気海洋相互作用の評価に利用できる可能性が示された。

• Title: Understanding tropical precipitation by using a global-coupled storm-resolving model
• Time: 13:30 - 15:00 on Sep. 4, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: Storm-resolving models show several advantages regarding the representation of different characteristics of tropical precipitation compared to models using statistical approaches to represent convection. The added values comprise the representation in the structure of convective systems (mesoscale convective systems, convective waves, tropical cyclones, among others) together with the spectrum of precipitation intensities, e.g., the frequency of light rainfall (< 20 mm d-1) is not overestimated. These points are outcomes of limited-area or global simulations, but in both cases with prescribed sea surface temperature, opening the question of whether resolving convection is enough to constrain the sea surface temperature (SST) pattern, and if the possible distortions could impact the structure of the tropical rainbelt and the spectrum of precipitation intensities. We use the global-coupled storm-resolving ICON model using the Sapphire configuration (ICON-Sapphire). On a regional scale, ICON-Sapphire represents the annual and seasonal structure and location of the tropical rainbelt over land, as well as over the Eastern Pacific and the Atlantic. Contrarily, the misrepresentation of the SST pattern in the Indo-Pacific (cold bias at the equator) distorts the structure of the rainbelt in this region, which presents a double band of precipitation. Thus, the SST pattern has a strong impact on the representation of the oceanic rainbelt but not over land. The bias in SST also does not affect the representation of the frequency of light rainfall in ICON-Sapphire, which present a spectrum of precipitation intensities similar to observations. Moreover, the added value of correctly representing the precipitation spectrum relies on the role of light and heavy precipitation intensities on the mean and variability of tropical precipitation. Heavy precipitation intensities (> 20 mm d-1) contribute to 60% of the total precipitation in the tropics, and the daily number of grid points categorized as heavy rainfall explains 80% of the tropical precipitation variability on a seasonal and daily time scale. Using observations produces similar results. Therefore, our analysis points out that by explicitly resolving convection with a grid spacing of 5 km, essential characteristics of tropical precipitation can be represented as the structure of the tropical rainbelt over land and the role of the heavy precipitation regime on the tropical precipitation variability.

• Title: Deep learning for climate prediction and projection
• Time: 15:30 - 17:00 on Aug. 7, 2023.
• Place: General Research Bldg. 2F room 270 and Zoom
• Abstract: I will demonstrate the potential advantages of utilizing deep learning for the climate prediction and projection. In the first part, I will show that a statistical forecast model employing a deep learning approach produces skillful ENSO forecast for lead times of up to one and a half years. Then, the recent development of the deep learning models for the ENSO forecasts will be introduced. In the second part, I will show that deep learning successfully detects the climate change signals embedded in daily precipitation fields during the observed record. We trained a convolutional neural network with daily precipitation fields and annual mean global mean surface air temperature data. After applying the algorithm to the observational precipitation dataset, I found that the daily precipitation data represented an excellent predictor for the observed planetary warming, and they showed significant deviations from natural variability since the mid-2010s.

• Title: 全球雲解像モデリングの現状：季節内スケールの現象理解と気候シミュレーションを例に
• Time: 10:00 - 11:30 on Jul. 26, 2023.
• Place: General Research Bldg. 2F room 270とZoomでのハイブリット開催（＊気候コロキウムと合同開催）
• Abstract: スーパーコンピュータ「富岳」に代表されるように、近年の計算機性能の向上は著しく、気象・気候モデリング研究も新たな展開を見せている。極端降水や台風、マッデン・ジュリアン振動（MJO）といった日〜季節内スケールの現象の理解や確率予測を目的とした O(1000)メンバーのアンサンブル実験や、全球kmスケールの水平解像度のもとでの気候シミュレーションはその一例であり、国内外を問わず精力的に進められつつある。この潮流のもと、発表者は全球非静力学モデルNICAMを用いて、1) 全5,000メンバーの巨大アンサンブル実験を活用したMJOの東進タイミングの決定特性の調査 や、2) 気候平均場と変動成分の再現性を両立するような全球雲解像気候実験（水平解像度3.5kmで10年）の実施とそれに向けたモデル改良・開発を手掛けてきた。本発表では、1) の研究によって得られたMJOの確率的な描像とその背後にあるメカニズム、および 2) における考え方と現状を中心に示す。また、発表者は5月末から約2ヶ月弱の間、ドイツのマックス・プランク気象研究所をベースに欧州に滞在し、主に降水・対流プロセスの観点から、全球kmスケールの ICON, IFS, NICAM による気候シミュレーションの比較解析も進めた。その結果についても、全球高解像度気候モデリングの国際的な現状の一例として紹介したい。

• Title: 気候変動の予測可能性研究、およびEvent Attribution研究ーこれまでの研究紹介ー
  Studies on climate predictability and Event Attribution -Introduction of my research to date-
• Time: 10:00 - 11:30 on Jun. 21, 2023.
• Place: General Research Bldg. 2F room 270とZoomでのハイブリット開催（＊気候コロキウムと合同開催）
• Abstract: 自己紹介を兼ねて、これまで発表者が行ってきた研究について紹介する。発表者は、熱帯の大気海洋相互作用を専門とし、CGCMにおけるENSOの振る舞いの改善や熱帯不安定波のパラメタリゼーションの導入などモデルの改良に関わる研究を手掛けた他、それらのモデルを用いてENSOやENSOが駆動する大気の変動を数カ月先まで予測する季節予測の予測可能性研究に従事してきた。 　前職の気象研究所では、実際に発生した極端現象に対する地球温暖化の影響を定量的に評価するEvent Attributionと呼ばれる研究に従事した。およそ10年前に誕生したEvent Attributionは、近年流行のラージアンサンブル実験の先駆けとなる研究手法であった。発表者は、高解像度のラージアンサンブル実験を予測可能性研究に応用する新しい取り組みも行っており、今後は対象を数年から数十年規模の自然変動にも広げて、メカニズム研究や予測可能性研究を進めていく計画である。
  This is an opportunity to introduce myself and my research to date. I specialize in tropical air-sea interaction and have been involved in research related to GCM improvements, such as improving the behavior of ENSO in CGCMs, introducing parameterization of tropical instability waves into OGCM, and so on. Using these GCMs, I have also been involved in research on seasonal predictability of ENSO and ENSO-driven atmospheric variability. In my previous position at the Meteorological Research Institute, I was involved in a research project called Event Attribution, which quantitatively and probabilistically evaluated the impacts of global warming on actual extreme events. Event Attribution, which was born about 10 years ago, was the pioneer of the technique of large ensemble simulations that have become popular in recent years. The presenter is also challenging research to introduce high-resolution large ensemble experiments into studies on climate predictability, and plans to expand the scope of the research to multi-annual to multi-decadal natural variability to study the mechanisms and predictability. Presentations will be given in Japanese, but slides are prepared in English, so please refer to them if you do not understand Japanese.

• Title: Dynamics of ENSO Diversity
• Time: 15:30 - 17:00 on Jun. 1, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: The El Nio/Southern Oscillation (ENSO) phenomenon exhibits in its sea surface temperature anomalies and associated fields with complicated spatiotemporal variations. Two main typical spatiotemporal patterns are known to be associated with the so-called the Central Pacific (CP) and Eastern Pacific (EP) El Nio events, which have significantly different longitudinal locations along the equator and temporal evolutions. This ENSO's diversity has great implications for various impacts on global climate systems and beyond. Understanding this ENSO diversity has been a subject under extensive research activity, as its fundamental mechanisms remain a key open research subject. Using a revised intermediate coupled model, we demonstrate that deterministic nonlinear processes can generate realistic ENSO CP and EP diversity via either period doubling or subharmonic resonance routes or both to chaos. The stochastic noise forcing may further expand the regime for this ENSO diversity. Thus, the nonlinear instability of the ENSO oscillator plays a fundamental role in its spatiotemporal diversity. This nonlinear dynamics of ENSO should be further examined for better understanding ENSO's predictability and ENSO's sensitivity under global warming.

• Title: Studying climate through a spectral lens
• Time: 10:30 - 12:00 on May. 15, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: Radiative transfer processes are intrinsically spectral dependent, yet this spectral dimension is not broadly utilized in physical climate studies. I will present three examples to illustrate the merit of spectral dimension in such studies, closely tied to relevant satellite observations. First, I will show how the longwave spectral flux derived from observations can be used in model diagnostics to reveal compensating biases that broadband diagnostics alone cannot tell in the radiative feedback analysis. Second, I will describe why two longwave processes, namely surface spectral emission and cloud longwave scattering, are missing in current climate models but should be included for a faithful simulation of polar climate. Third, I will briefly describe the implication of the most recent NASA solar spectral irradiance measurements from TSIS-1 on the International Space Station, especially the partition between visible and near-infrared, for high-latitude climate simulation.

• Title: Thoughts on CMIP and the future of climate science
• Time: 10:00 - 11:30 on Apr. 27, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: With the arrival of climate change, and the acceptance of the basic tenets of climate science, we are entering a new era. These changes are colored by an explosion of computational capacity, supporting machine learning and high-resolution simulation and increasing interest by the private sector. In this talk I share some thoughts on what these changes mean for how we structure our science, and in so doing present my ideas, and our activities, in relation to high-level international activities such as CMIP, Destination Earth, EVE, and the Berlin Summit.

• Title: The interrelationship of tropical cyclogenesis over the different basins
• Time: 13:30 - 15:00 on Apr. 27, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: The present study investigates the interrelationship of tropical cyclone (TC) genesis among the western North Pacific (WNP), eastern North Pacific (ENP), and tropical North Atlantic Ocean (TNA) from 1979 to 2020. Two related works are introduced in combination. One work found the coherent interannual variation of TC genesis among the southeastern part of the WNP (SEW for brevity), ENP and TNA during the TC peak season. Correlation analysis shows there is a significant positive (negative) relationship between the SEW/ENP (TNA) TC genesis and a tripole zonal sea surface temperatures (SST) anomaly distribution among the central and eastern Pacific Ocean (CEP), western Pacific and tropical Atlantic Ocean. Another work found a significantly out-of-phase variation between spring (MAM) TC genesis over the WNP and the following summer-fall (JJASON) TC genesis over the SCS. Composite analysis and numerical model experiments show that negative SST anomalies during MAM in the tropical CEP and southeastern Indian Ocean work together to induce a lower-level cyclonic circulation over the WNP, with the latter more important. In following JJASON, the SST anomalies are reversed in the tropical CEP. The positive precipitation anomalies over the western-central Pacific induced by positive SST anomalies further stimulate an anomalous zonal overturning circulation with anomalous descending motion and boundary layer divergence over the SCS. In addition, the persistent negative SST anomalies around the Maritime Continent (MC) induce an anomalous anticyclone to the west. Both processes inhibit the TC genesis over the SCS. The simultaneous relationship of TC genesis among SEW, ENP and TNA and the out-of-phase relationship of TC genesis between the WNP and SCS also exist when the El Nio-Southern Oscillation (ENSO) years are removed.

• Title: Use of trace gas measurements to quantify convective transport pathways toward developing a new transport diagnostic and metric
• Time: 13:30 - 15:00 on Apr. 6, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: Convective transport from the marine boundary layer (MBL) to the upper troposphere (UT) is investigated using airborne in situ measurements of chemical tracers over the tropical western Pacific (TWP). Using 42 trace gas species with photochemical lifetimes ranging from shorter than a day to multiple decades, we developed a diagnostic called Transit Time Distribution, G(t) to characterize convective transport time scales associated with UT air parcels sampled over the convectively dominant TWP region. G(t) describes relative contributions of air masses transported from the MBL to the UT via all transport paths with different transit times (see the schematic illustration below). We further demonstrate that the tracer-derived transit time scale is broadly comparable to that estimated from convective mass flux and Lagrangian trajectory analysis. The observation-based Transit Time Distribution not only provides insights into convective transport pathways, but also has the potential to serve as an effective metric for evaluating the representation of convective transport in global models.

• Title: From High-Resolution to Global Storm Resolving Models: achievements and perspectives
• Time: 15:00 - 16:30 on Apr. 6, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: Increasing available high-performance computing has enabled global coupled models to resolve some of the fundamental processes governing the climate system. More explicit representation of eddies in the ocean and of weather systems in the atmosphere impacts the general circulation and reduces inter-model disagreement. More realistic simulation of the global hydrological cycle at resolutions beyond 50km underpins more trustworthy projections of the availability of heat, carbon and water to land vs ocean ecosystems. Global “Weather-Resolving” models produce reliable global teleconnections that govern regional changes in weather and climate, including extremes (e.g. Tropical Cyclones). Resolving the ocean mesoscale produces “out of trajectory” future climates for Europe. Global Storm Resolving Models now operate in the resolution range of 1-10 km, removing some long-standing errors in the simulation of precipitation (location, organization, diurnal cycle, intensity/frequency). However, uncertainties remain with respect to the adequateness of key parametrisations at such scales, motivating research on global cloud-resolving capability.

• Title: Clouds and precipitation in two versions of the Energy Exascale Earth System Model (E3SM)
• Time: 13:00 - 14:30 on Apr. 4, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: As part of the US Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM) project, two versions of climate models are currently being developed. The 100-km scale version 3 of the E3SM Atmosphere Model (EAMv3) and a 3.25km scale Simple Cloud Resolving E3SM Atmosphere Model (SCREAM). In this talk, I will present early results of clouds and precipitation in these two model configurations. Compared to earlier versions of the model, EAMv3 employs a new microphysics scheme (P3) and a range of new deep convection enhancements that help to represent the impacts of meso-scale convection, the impact of large-scale circulations on convection, and a more sophisticated convective cloud microphysics scheme that allows for aerosol effects. These new adjustments improve the tropical and diurnal variability in clouds and precipitation, while also maintaining the mean-state patterns of precipitation. Results from a pair of 30-year present-day and +4K warmed SST simulations will be discussed, regarding the impact of the new physics on cloud and precipitation responses.

• Title: Use of LES case studies for improving cloud physics in large-scale models
• Time: 14:30 - 16:00 on Apr. 4, 2023.
• Place: General Research Bldg. 2F room 270
• Abstract: The most recent Earth system model development cycle at NASA GISS relied heavily on side-by-side comparison of large-eddy simulation (LES) case studies with GISS-ModelE3 run in single-column model (SCM) mode. Introduction of a moist turbulence scheme was first tested against clear-sky boundary layer cases. Adding two-moment stratiform microphysics with prognostic precipitation was tested against stratocumulus, cumulus, transition, mixed-phase, cirrus and deep convection cases. A recently developed case of highly supercooled mixed-phase stratus observed over Antarctica during the DOE AWARE campaign is highlighted to demonstrate derivation of microphysical process parameter uncertainty ranges as input to a machine learning tuning process. New cases currently under development for use in the next round of GISS-ModelE3 development are being derived from several recent field campaigns (DOE COMBLE and TRACER, and NASA CAMP2Ex and SEAC4RS), including three general improvements. First, new cases are all taking a cloud-following Lagrangian approach, starting with cloud-free conditions and tracking cloud life cycle. Second, each case includes realistic aerosol size distributions based on observations, suitable to test prognostic droplet activation, primary ice formation, and aerosol wet scavenging. Third, several diverse cases of target regimes are being derived from each campaign, thus providing a stronger test of physics across varying conditions (e.g., range of cold-air outbreak index). The availability and development of well-constrained LES/SCM case studies has revealed several additional applications beyond the main objective of providing a benchmark for handling uncertain microphysical processes: namely, the LES/SCM case studies have proved useful for testing instrument simulators, evaluating satellite data products used for large-scale model tuning, and studying retrieval algorithms. For instance, development of a new ground-based radar-lidar forward simulator software (the Earth Model Column Collaboratory package) was tested against LES and SCM output for the AWARE case, enabling a confident interpretation of simulator and model performances against observed quantities, and a similar test of a satellite lidar simulator against the well-constrained SCM results led to substantial changes in evaluation conclusions. In addition, the process of seeking to well constrain multiple Lagrangian case studies revealed discrepancies in liquid water path retrieval products and a recommendation to revise product use for GISS-ModelE3 tuning using machine learning. Finally, past LES case studies with realistic aerosol and hydrometeor particle size distributions (using a size-resolved microphysics modeling approach) have been used to test detection of multimodal drop size distributions using multi-angle polarimeter measurements, suggesting an improved route versus use of idealized simulations (e.g., with fixed droplet number concentration). In closing, it is proposed that developing realistic aerosol-to-precipitation LES simulacra of cloud life cycles observed during field campaigns can offer a strong foundational activity for large-scale model physics improvement, providing a clearly actionable pathway to improve the representation of cloud processes, as well as retrievals and model evaluation tools.

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