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: Improving systematic errors in clouds and radiation in global models（仮）
• Time: 13:30 - 15:00 on Mar. 22, 2023.
• Place: 270室(General Research Bldg. 2F room 270)
• Abstract: TBD

• Title: Global impact of recent Southern Ocean cooling
• Time: 15:30 - 16:30 on Feb. 2, 2023.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Since the beginning of the satellite era, Southern Ocean sea surface temperatures (SSTs) have cooled, despite global warming. While observed Southern Ocean cooling has previously been reported to have minimal impact on the tropical Pacific, the efficiency of this teleconnection has recently shown to be mediated by subtropical cloud feedbacks that are highly model-dependent. Here, we conduct a coupled model inter-comparison of paired ensemble simulations under historical radiative forcing: one with freely evolving SSTs and the other with Southern Ocean SST anomalies constrained to follow observations. We reveal a global impact of observed Southern Ocean cooling in the model with stronger (and more realistic) cloud feedbacks, including Antarctic sea-ice expansion, southeastern tropical Pacific cooling, northward-shifted Hadley circulation, Aleutian Low weakening, and North Pacific warming. Our results therefore suggest that observed Southern Ocean SST cooling might have contributed to cooler conditions in the eastern tropical Pacific in recent decades. This remotely driven eastern tropical Pacific cooling is shown to halve the bias in global radiative feedback during the historical period in coupled simulations.

• Title: Ensemble Simulations of the climate and ice sheets of the Last Glacial Maximum with a climate-ice sheet coupled model
• Time: 10:00 - 11:00 on Jan. 10, 2023.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Simulating past climates and ice sheets that largely differ from today with climate-ice sheet models is essential to evaluate the their performance and to improve our confidence of future sea level projections. The Last Glacial Maximum is a good target period for this purpose as the global climate was colder by 6K and additional ice sheets of 120m sea level equivalent expanded over the northern continent. Here we performed ensemble simulations of the climate and ice sheets at the Last Glacial Maximum with a recently developed ice sheet-climate coupled model Famous-Bisicles. From these ensemble simulations, we aim to check whether the model reproduces the ice sheets reasonably well and to learn what parameters play a role in controlling the ice volume as well as the global climate. Roles of clouds, albedo and ice sheet basal drag parameters on the climate and ice sheets will be discussed.

• 場所: 270室＋Zoomによる開催（予定）

• Title: イギリス気象庁気候モデルの雲フィードバック過大評価の理解、改善へ向けて：中緯度の雲
• Time: 13:30 - 14:30 on Dec. 15, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: 雲フィードバックは長年気候感度のばらつきの最大不確定要素である。近年その理解のために地表気温、 安定度、700hPaおよび対流圏上層の相対湿度、および500hPaの鉛直流速度など雲に影響を与える大気要素 (cloud controlling factors: 以下c-factors)を使った解析が盛んに進められている。それらの研究の一つ、 Ceppi and Nowack (2021)はridge regression手法をCMIP5,CMIP6の大気海洋結合モデルの出力に適用し、 諸モデルの温暖化に伴う雲のフィードバックが、温暖化に伴う地表気温、安定度の変化、そして現在気候における 雲の放射効果のそれらの要素に対する感度を用いることで良く再現されることを示した。 同様の解析を最新のイギリス気象庁全球大気モデル(HadGEM3 GA8)のPerturbed Parameter Ensemble(PPE)に適用したところ、 中緯度海上の雲の放射効果がc-factorsに対し観測が示すよりも過敏であり、中層雲の感度が特にその傾向と合致することが分かった。 太平洋では雲は黒潮、親潮およびその境界領域に該当し、太平洋に領域を限定した雲の季節変化の基礎解析を行ったところ、 特に寒流である親潮領域の雲の季節変化がモデルで観測と大きくことなることが分かった。 今回の滞在中、GPM、CloudSatなどの観測データを用い、これらの領域の季節変化に伴うc-factorsの変化、雲の変化について 理解を深めようとしている。一方PPEの解析から、この領域の雲の放射効果のc-factorsへの感度に影響のある諸パラメター及び 観測の感度を得るためのパラメター値の範囲を見積もることができる。現在提案中のタスクについても紹介する。

• Title: Global multi-centennial coupled climate modelling towards 10km resolution
• Time: 13:30 - 15:00 on Nov. 21, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: There is increasing evidence of the importance of improved representation of both the ocean mesoscale and corresponding scales in the atmosphere in global climate models, in order to better understand future climate risk. The Met Office is developing a physical climate model aiming at 10km grid spacings in both atmosphere and ocean, with a view to simulating the full CMIP6 1850-2100 period. The work will build on the understanding gained from CMIP6 HighResMIP and from EU PRIMAVERA while also relaxing some of the constraints used there, such as short ocean spin-up and simplified aerosol forcing. New model components developed since CMIP6, such as a new atmosphere convection scheme, will also be incorporated to improve aspects of large-scale model biases and smaller scales such as cyclone intensities. Such models are increasingly challenging our standard methods of data output, storage, sharing and analysis, particularly given their improved capabilities to represent high impact weather and hence the need for high frequency output. The project is developing software tools to be run inline with the model simulations, in order to automate analyses such as storm and eddy tracking and frontal diagnosis, with the potential to reduce the storage footprint while speeding up scientific insight. This work is also engaged with the HighResMIP community and its evolving plans for new science questions and experimental protocols post-CMIP6. It is also a part of a new EU project EERIE (beginning in 2023) led by Thomas Jung, in which four European models will produce simulations at around 10km resolution, initially using the HighResMIP simulation design, to better understand the role of the ocean mesoscale on climate.

• Time: 10:00 - 12:00 on Oct. 19, 2022.
• Place: 270室(General Research Bldg. 2F room 270)
• Title and Abstract:
  ・Modelling the evolution of the Greenland ice sheet during the Last Intergl acial period (Dr. Marie Sicard)
  The Last Interglacial (129-116 ka BP; LIG) is one of the warmest periods in the last 800 ka at many locations with a maximum surface temperature increase in the high latitude of the Northern Hemisphere. This period provides a good testing ground to evaluate the ice sheet-climate interactions under warmer conditions than today. We conducted a transient simulation over the interval from 130 to 120 ka using the GRISLI ice sheet model forced by several snapshots run with the IPSL-CM5A2-VLR model. As a result of climate change over the Last Interglacial, the GRISLI ice sheet model simulates a Greenland ice loss of 10.7-57.1 %, corresponding to a GMSL rise of 0.83-4.35 m and a 0.2 C additional warming in the Arctic region. To better assess ice sheet-climate feedbacks in the Arctic, we therefore carried out a preliminary study using the icoLMDZOR model that includes the new dynamical core DYNAMICO developed at the Institut Pierre-Simon Laplace (IPSL). This study shows that the use of high-resolution atmospheric fields improves the calculation of the surface mass balance in Greenland.
  ・Last-Interglacial Arctic sea-ice simulated by the CMIP6/PMIP4 climate models - an overview (Dr. Marie Sicard)
  The 16 models that run the Last Interglacial (LIG) experiment as part of the CMIP6/PMIP4 exercise consistently produce a smaller Arctic summer sea-ice area at 127 ka BP relative to the pre-industrial period. However, they do not agree on the magnitude of this decrease. This large spread between climate models is partly explained by differences in representation of melt-ponds and cloud microphysics, which affects radiation fluxes over sea-ice. News investigations showed similar sea-ice distribution in the central Arctic between the LIG experiment and an idealized simulation of the near-future climate, but a different sea-ice loss pattern in the Atlantic sector. Climate models generally simulate more sea ice East of Greenland and less sea ice over the Barents Sea for the near-future compared to the LIG. East of Greenland, changes in sea ice are due to a strengthening of the northern winds. In the Barents Sea, the increased sea-ice melt is driven by a warming of the Atlantic Waters along their poleward pathway.
  ・The greenland icesheet during Pliocene (Dr. Gilles Ramstein)
  We first used Pliomip1 simulations using IPSL CM5 climate model and GRISLI in a one-way coupling and different sensitivity experiments (pCO2, insolation) to investigate the full glaciation of Greenland icesheet during late Pliocene (Contoux et. Al, EPSL 2015). We then used an asynchronous coupling method previously developped for Antarctica by Ladant et. Al Paleoceanography 2014 ou 2015), based on 56 sensitivity simulations that enable us to produce different transient simulations driven by different Pco2 scenarios and computed insolation from Laskar (2004). One of the results demonstrates that a CO2 threshold is necessary to build and melt part of the icesheets with insolation forcing. The second important result is to validate which pCO2 scenarios reconstructed from data is the most realistic (Tan et. Al 2019 ou 1017 Nature comm).
  ・Coupled ice sheet : climate simulations of the last two glacial terminations (Dr. Aurlien Quiquet)
  The deglaciation of the Quaternary offers an unique opportunity to understand the climate--ice-sheet interactions in a global warming context. To tackle this question, we use here an ice sheet model synchronously coupled to an Earth system model of intermediate complexity to simulate the last two deglaciations. For the last deglaciation, we show that our simulated ice sheet geometry evolution is in overall good agreement with available global reconstructions. Large-scale grounding line instabilities are simulated both for the Eurasian and North American ice sheets even though the past abrupt sea level rises are underestimated, possibly because the climate model underestimates the millenial-scale temperature variability. In our model, Atlantic oceanic circulation is strongly sensitive to freshwater flux from ice sheet melting and abrupt warming phases in Greenland are linked to oceanic circulation recoveries. The penultimate deglaciation resembles the last deglaciation with a more rapid ice sheet collapse because of stronger insolation forcing. Our model produces a Greenland ice sheet contribution to sea level rise during the last interglacial of about 2 m of sea level equivalent, in agreement with most recent estimates.

• Title: A Super Best Track for Tropical Cyclone Forecasting & Research
• Time: 10:00 - 11:30 on Oct. 17, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Deterministic tropical cyclone (TC) track forecasts have become so accurate in the medium range (e.g., the mean 72-h position error of the global models is now below predictability 'limits') that I expect tropical cyclone (TC) forecasting to move in new directions that include: 1) a more explicit (and better) prediction of the surface wind field; and 2) 'completing the forecast' with predictions of genesis (and dissipation). Additionally, the availability of high-resolution/high-quality global reanalyses will allow more dynamical studies of long-term TC variability.
  Current best track data sets have several deficiencies that limit both research and forecasting since they lack:
  * position/intensity/structure data in the pre/potential TC (pTC) genesis stage
  * observational analyses of the surface wind field and precipitation
  * a ‘diagnostic file,’ with environmental and storm variables known to be related to intensity and structure change (e.g., vertical wind shear)
  The foundation of the super best track (BT++) is the 'final' best tracks ofthe two US operational forecast centers - the Joint Typhoon Warning Center (JTWC) and the National Hurricane Center (NHC). The BT++ is thus global and unique in three important ways by including:
  * pTC tracks taken from a curated archive of all (both 'numbered' and INVEST or 9X systems) working best track data from JTWC/NHC since 2005
  * dynamical environmental variables (analysis and forecasts) come the latest ECMWF reanalysis - ERA5 - that uses a model with the same resolution as the NWP global models circa 2015
  * satellite precipitation and wind radii from surface wind analyses
  The initial version of the BT++ covers a 15-year period 2007-2021 and after a brief summary of BT++ properties, the talk gives one application example for TC genesis. In a preliminary BT++, using operational ECMWF analyses/forecasts, we examined the difference between developing and non-developing pTCs. While there was a clear signal of vertical wind shear decreasing 48-72 before genesis, a more surprising result was that the global model vortex also intensified in the developing cases.
  The paper concludes with a discussion of other potential science and forecasting applications.

• 場所: 270室＋Zoomによる開催

• Title: Atmospheric nonspherical particles: Toward advanced cloud-aerosol remote sensing
• Time: 13:30 - 15:00 on May. 26, 2022.
• Place: 270室およびZoomによる開催(General Research Bldg. 2F room 270 and Zoom)
• Abstract: Spaceborne cloud-aerosol property retrievals have been widely used not only for climate studies and validations of numerical modeling capabilities but also nowadays process-oriented microphysics studies. However, these satellite-based cloud-aerosol products may involve systematic biases and/or uncertainties primarily due to inappropriate assumptions made in the retrieval algorithms. In particular, the particle shape models assumed in the retrieval algorithms are generally much simpler than those in nature that exhibit a variety of particle sizes and nonspherical shapes. In this presentation, I will first briefly review cloud-aerosol remote sensing and the importance of the relevant assumptions of atmospheric nonspherical particles in remote sensing. Next, I will introduce a recently developed comprehensive database for the single-scattering properties of irregular aerosol particles (the so-called TAMUdust2020 database) for mineral dust optical property models as an example. The new mineral dust optical property model assumes an ensemble of various irregular particle shapes that mimic realistic mineral dust particle shapes and their diversity and is developed with state-of-the-art light scattering computational capabilities. Furthermore, I will describe the potential applications of the new optical property model to multi-satellite-based remote sensing of dust aerosols, including spaceborne active and passive sensor observations. If time allows, I will describe an example of an active-passive combined remote sensing of cloud properties for cloud microphysics studies.
  References: Saito et al.,(2021) J. Atmos. Sci., 78, 2089-2111; Saito and Yang, (2021) Geophys. Res. Lett., 48, e2021G095121.

• Title: 海洋生態系・物質循環に対する人為起源の栄養塩流入の影響
• Time: 13:30 - 15:00 on Apr. 21, 2022.
• Place: 270室およびZoomによる開催
• 要旨：化石燃料の燃焼や農業用の化学肥料の利用などの人間活動は、大気と河川から海洋への栄養塩(窒素や鉄など)の流入を大幅に増加させている。このような富栄養化は基礎生産を増加させ、気候変動による減少を一部打ち消す可能性がある。また、海洋内部への有機物の輸送とその分解を増やすため、炭素の吸収を促進し、気候変動による海洋の脱酸素化を増幅させる。しかし、CMIP5の地球システムモデルなどでは人為起源の栄養塩流入の影響は考慮されていない。そのため、このような擾乱が海洋の生物地球化学循環に与える影響についての理解は、気候変動の影響の理解に比べ不十分である。特に、気候変動の影響と、人為起源の栄養塩流入の影響との定量的な関係は、ほとんど理解されていない。 本研究では、大気と河川からの人為起源の栄養塩流入を考慮したCMIP6モデルの一つ（MIROC-ES2L）によるヒストリカル実験を用いて、海洋基礎生産量、炭素吸収量、溶存酸素インベントリーの変化に対する人為起源の栄養塩流入の寄与が気候変動の寄与と同程度であることを示す。特に、 (1)富栄養化は、海洋の温暖化と成層化に伴う基礎生産の減少を打ち消す以上の効果がある、(2)気候変動に伴う海洋上層の貧酸素化を加速し、モデルと観測の不整合の一部を補う、という2つの注目すべき結果が得られた。これらの結果から、海洋の生物地球化学循環に対する人間活動の影響を評価するためには、栄養塩流入と気候変動の両方の影響を考慮することが重要であることがわかった。

• Title: Co-evolution of atmospheric oxygen level and marine biogeochemical cycles on early Earth
  初期地球の大気酸素濃度と海洋物質循環系の共進化についての理論的研究
• Time: 13:30 - 15:00 on Apr. 14, 2022.
• Place: 270室およびZoomによる開催
• 要旨：地球史初期の太古代（40-25億年前）の地球は大気酸素濃度は現在より6桁以上小さい無酸素条件下にあったと考えられている。一方、その後の原生代初期の約24-22億年前には大気酸素濃度が現在の数％程度まで一気に上昇する「大酸化イベント」が発生したと考えられている。この大酸化イベントを駆動するためには酸素を多量に放出できる酸素発生型光合成生物が海洋中に存在することが必要であるが、酸素発生型光合成生物はこの大酸化イベントから数億年以上先んじて登場していたのではないかということが、地質学的・系統学的に議論されている。私はそのような無酸素条件の太古代の酸素発生型光合成生物の登場後から原生代にかけての大気-海洋-生態系-気候の共進化について、これまで主に鉛直一次元大気光化学系モデルと海洋生物地球化学循環ボックスモデルを用いて理論的な検討を進めてきた。今回の発表ではその背景となる知識について紹介した上で、これらの成果について議論を行いたい。

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