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: TBD
• Time: 10:00 - 11:30 on Oct. 9, 2024.
• Place: General Research Bldg. 2F room 270（＊気候コロキウムと合同開催）
• Abstract: TBD

• Title: Tropical Pacific responses to idealized subtropical low cloud forcing through subsurface oceanic adjustment
• Time: 15:30 - 16:30 on Aug. 28, 2024.
• Place: General Research Bldg. 2F room 270
• Abstract:TBD

• Title: Dissecting climate and climate models with the aid of radiative kernels
• Time: 13:30 - 15:00 on Jul. 25, 2024.
• Place: General Research Bldg. 2F room 270
• Abstract: Radiation is a crucial shaping factor of the Earth climate. Based on the global reanalysis data (ERA5), we have produced a new set of radiative kernels that can be used for diagnosing the radiation budgets at the Top-of-Atmosphere (TOA), surface and inside the atmosphere. In this talk, I will exemplify the use of the radiative kernels in different applications. The first case is an analysis of the "radiator fin" effect of the Arctic in the warming climate. This effect refers to a distinct positive trend of the Earth thermal radiation in the Arctic, which has been observed by the satellites in the past two decades. This effect acts to radiate excess heating accumulating in the climate system to the space during global warming. Using the aid of the band-by-band radiative kernels, we find that compared with other regions such as the tropics, the prominent thermal radiation trend in the Arctic results from a stronger surface and atmospheric warming and a less offsetting greenhouse effect of water vapor. The second case is a critical examination of the Global Climate Models (GCMs). Given the importance of the radiation budget, GCMs are often validated with regard to their simulated TOA radiation fluxes. Here we use the radiative kernels to diagnose the radiation biases in the CMIP6 GCMs. We find that many of them have a cold air temperature bias and a moist tropospheric humidity bias, which lead to considerable TOA radiation biases but are compensated by cloud-induced biases. These findings disclose that seemingly good radiation simulations can be due to compensating errors. This possibility can and should be checked with kernels during GCM development.

• Title: イベントアトリビューション迅速化のための新手法
• Time: 10:00 - 11:30 on Jul. 24, 2024.
• Place: General Research Bldg. 2F room 270（＊気候コロキウムと合同開催）
• Abstract: この１０年ほど地球温暖化の加速とともに、全球的に熱波や豪雨が頻発しており、極端気象に対する人為的気候変動の影響を見積もるイベントアトリビューション(EA)の迅速化が求められている。従来のEAは、全球モデルや領域気候モデルによるダウンスケーリングによる大規模アンサンブル実験を実施した後で行うため、公表までに時間を要した。そこで、既存のデータのみを用いて、統計的にかつ迅速に気候変化影響を推定する新EA手法を開発した。日本の気象現象は、熱帯-中緯度域の海面水温偏差とそれに伴う大気循環場に影響を受ける事が知られているが、新手法は極端イベント発生時の海洋背景場の影響が考慮されている事が特徴である。発表では、新手法と日本の極端高温イベントへの適用例について紹介する。

• Title: Tropical Deep Convection, Cloud Feedbacks and Climate Sensitivity
• Time: 10:00 - 11:30 on Jul. 16, 2024.
• Place: General Research Bldg. 2F room 270
• Abstract: The lecture is concerned with how the diabatically-forced overturning circulations of the atmosphere, established by the deep convection within the tropical trough zone (TTZ), first introduced by Riehl and Simpson (1979), fundamentally shape the distributions of tropical and sub-tropical cloudiness and the changes to cloudiness as Earth warms. The talk first draws on analysis of a range of observations to understand the connections between the energetics of the TTZ, convection and clouds. These observations reveal a tight coupling of the two main components of the diabatic heating, the cloud component of radiative heating, shaped mostly by high clouds formed by deep convection, and the latent heating associated with the precipitation. Interannual variability of the TTZ reveal a marked variation that connects the depth of the tropical troposphere, the depth of convection, the thickness of high clouds and the TOA radiative imbalance. The study the examines connections between this convective zone and cloud changes further afield in the context of CMIP6 model experiments of climate warming. The warming realized in the CMIP6 SSP5-8.5 scenario multi-model experiments, for example, produces an enhanced Hadley circulation with increased heating in the zone of tropical deep convection and increased radiative colling and subsidence in the sub-tropical regions that then impacts low cloud changes and in turn the model warming response through low cloud feedbacks. The pattern of warming produced by models, also influenced by convection in the tropical region, also has a profound influence on the projected global warming.

• Title: Evaluating fine-scale ESMs for Southeast Asian Climate and Extreme
• Time: 15:00 - 16:30 on May 29, 2024.
• Place: General Research Bldg. 2F room 270
• Abstract: Even state-of-the-art CMIP-class Earth system models (ESMs) still exhibit biases in simulating realistic climate state and these biases are source of uncertainties in climate prediction and projection. One of possible solutions could be a refinement of model’s resolution like High-ResMIP. Towards this direction, NextGEMS project (EU Horizon 2020) is developing European “storm-resolving” ESMs whose resolution is a range of 10km to a few km (atmosphere and ocean) globally. 　This very fine resolution allows us to investigate climate, air-sea interaction, and extreme weather in marginal oceanic areas where common CMIP6 might have difficulty to resolve properly. This study assesses how 10km-resolution ESMs from NextGEMS project and other fine-resolution ESM can reproduce the climate and some extreme weather (wet and dry) in Southeast Asia that is related strongly to monsoon system, comparing to observation and some of CMIP6 ESMs. 　In the seminar, I will focus more on winter monsoon season (Dec-Jan-Feb) and show some preliminary results of this verification. (*セミナーは日本語で開催)

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