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: 13:30 - 15:00 on Apr. 20, 2018.
• Place: General Research Bldg. 2F room 270.
• Abstract: TBD

• Title: Space-Time Spectral Analysis of Moist Static Energy Budget Equation
• Time: 13:30 - 15:00 on Feb. 22, 2018.
• Place: General Research Bldg. 2F room 270.
• Abstract: Budgets of column-integrated moist static energy (MSE) are analyzed in the spectral domain, making use of ERA-Interim reanalysis data. The MSE budget is known as a useful tool for understanding the tropical disturbances including meso-scale cloud systems, convectively-coupled equatorial waves (CCEWs), intra-seasonal variation (or MJO) and others. The evolution of MSE is usually regressed against (or composited around) precipitation anomalies associated with a particular type of the disturbance, and the relative importance of each term in MSE budget equation to the charging and discharging mechanisms of MSE is qualitatively and quantitatively discussed. Here, we extend such approach to the spectral domain, utilizing the cross-spectrum between precipitation and some terms in MSE budget equation. The analysis method presented in this work is mathematically equivalent to the (traditional) regression analysis, if the analysis domain covers the entire tropical-belt, and does not reveal quite new features which have not been recognized yet. Nevertheless, we believe that this framework would be highly useful to grasp the different characteristics of a variety of tropical disturbances at a glance. Moreover, it would also gives us some insights about which proposed theoretical model is most plausible to explain the actual evolution of the precipitation disturbance in the tropics, because a theoretical model generally searches for the necessary condition for small moisture (or precipitation) perturbations to exponentially amplify, assuming a wave-like solution in a linearized MSE equation, and the modeled phase relationship and coherency are often the key for the unstable condition.

• Title: Machine Learning-based downscaling of GCM: Realizing CIMP-5 future simulations at a catchment scales with advanced data transformative models
• Time: 15:30 - 17:00 on Jan. 19, 2018.
• Place: General Research Bldg. 2F room 270.
• Abstract: In this seminar I will discuss predictive modelling with artificial intelligence tools, utilizing big data analytics for forecasting. The seminar will describe very briefly big data principles with minimum technical details but it with make a greater focus on application and results. In the application space I will provide case studies published in recent papers demonstrating the strength of advanced data analytic models in real-life. Part 1: One particular example would on machine learning-based downscaling of FAO-56 reference evapotranspiration (ETo) using artificial intelligence methods, constructed with an extreme-learning machine (ELM) and support vector regression (SVR) in a mountainous inland watershed in north-west China. In this example eight global climate model (GCM) outputs retrieved from the Coupled Model Inter-comparison Project Phase 5 (CMIP5) have been employed to downscale the monthly ET0 for the historical period 1960-2005 as a validation approach and for the future 2010-2099 as a projection of the ET0 under Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. The results will show the downscaling accuracies for near-term projection(2010-2039), mid-term projection(2040-2069), and long-term projection(2070-2099) under the RCP4.5 (RCP8.5) scenarios and demonstrate artificial intelligence models as useful in water-management policies. Part 2: Models considered will include, but not limited to, the extreme learning machine, support vector machine, multivariate adaptive regression spline and M5 Tree. I will also show results of studies that apply model optimisation tools, with meta-heuristic feature selection (or 'search') algorithms, feature weight optimisation (or'add-in') algorithms and multi-resolution tools such as wavelet transformation. These are applied to model the input-target data to improve the final prediction result. Feature selection is required to screen optimal input features, improve the accuracy and to reduce computational burden, whereas add-in algorithms can extract most, if not all of the predictive features from a large pool of carefully screened variables. Wavelet transformation, on the other hand, can assist in identifying frequency components in inputs and address issues of non-stationarity, trends, jumps and periodicities in model data. This seminar to reveal the role of ancillary tools in predictive modelling with particular applications of artificial intelligence models in water, drought, streamflow, global solar energy and agricultural yield simulation. Part 3: The seminar will discuss and expect to exchange ideas and challenges that we as, researchers face in predictive modelling that must be considered in practical models used in real-life to design decision-support systems, and in particular, how such models can be used in the downscaling of Global Climate Models.

• 場所: 総合研究棟　4センター共用2階会議室 270

• Title: Nonlinear Bjerknes feedback for asymmetric feature of ENSO
• Time: 15:30 - 17:00 on Dec. 21, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: La Nina is not a simple mirror image of El Nino. They have many asymmetrical features including amplitude, duration, pattern, and transition. In this talk, I would like to introduce a concept of ‘nonlinear Bjerknes feedback’ and address what are the origins of amplitude and transition asymmetries between El Nino and La Nina and its future change. To clarify the origin of amplitude asymmetry, Bjerknes Stability Index (BJ index) was computed for El Nino and La Nina events separately. The largest difference in the BJ index (i.e., growth rate) was found in the dynamical feedback. In particular, the enhanced sensitivity of the ocean dynamic response to wind stress during El Nino is a primary cause for the increase in the dynamical feedbacks, and is originated from the atmospheric nonlinear response to SST anomalies. To understand why El Nino is frequently followed by La Nina but not the opposite case, we analyze the inherent asymmetricities in a delayed negative feedback process within the delayed-oscillator framework. We found that the asymmetrical response of the ocean wave to wind is primary factor to the asymmetric transition. Finally, the future change in the transition asymmetry of ENSO is analyzed using CMIP5 scenario runs. Asymmetric transition feature in RCP4.5 is weaker compared to that in historical run, which turns out to be related to a loosen asymmetry in ocean dynamic response to wind.
  reference)
  1. S.-I. An, and J.-W. Kim, 2017: Role of nonlinear ocean dynamic response to wind on the asymmetrical transition of El Nino and La Nina. Geophy. Res. Lett., 44, 393-400.
  2. Im, S.-H., S.-I. An, S. T. Kim, and F.-F. Jin. 2015: Feedback processes responsible for El Nino-La Nina amplitude asymmetry. Geophys. Res. Lett., 42, 5556-5563.

• Title: Snapshots from the Future
• Time: 13:30 - 15:00 on Dec. 15, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: In this talk I will summarize the strategy we have been following to advance the use of high performance computing for climate prediction. I will do so: (i) by presenting a range of simulations, with grid scales that range from millimeters to kilometers over domains that range from a few meters to the global; (ii) by introducing the problems these have been applied to; and (iii) by outlining some of the insights that have been obtained from these studies. A central theme will be the role of small scales on the representation of cloud and convection controlling processes, and in presenting my view for the prospects for a radically new description of the climate system using techniques pioneered over the years by many members of my anticipated audience.

• Title: Satellites, Science, and Societal Benefits: Earth Science and Applications from Space
• Time: 10:00 - 11:15 on Dec. 1, 2017.
• Place: General Research Bldg. 2F room 270.

• Title: Effect of Climate Changes over Southeast Asia and Adjacent Regions on Global Climate
• Time: 15:00 - 16:00 on Oct. 24, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: Apparent climate change signals have been found in Southeast Asia and adjacent regions in the past decades. For example, the sea surface temperature has risen clearly in these regions and the tropical atmospheric heating has enhanced most strongly over the Maritime Continent and adjacent areas. Experiments with multiple earth system models including the NCAR CESM indicate that that these regional climate change signals exert significant influences on the global climate. Associated changes have included the weakened monsoons over India and the Arabian Sea, the declining Sahel rainfall, the well-observed drying tendency in East Asia, and lower-frequency ENSO cycle. The change in sea surface temperature associated with the shift between eastern Pacific El Nino and central Pacific El Nino even inhibits summertime Artic warming and thus sea-ice melting over the Canada Basin. Furthermore, the change in atmospheric heating over Southeast Asia and the western Pacific is related to changes in the mid-Pacific trough and thus the climate over North and Central America.

• Title: Observations of Stratospheric Normal Modes and their Association with Tropospheric Convection and the Quasi-biennial Oscillation
• Time: 13:30 - 15:00 on Oct. 6, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: The structure and temporal variability of stratospheric mixed Rossby-gravity, Kelvin, westward inertio-gravity, and external Rossby waves is isolated through an EOF analysis of space-time filtered equatorial wind and geopotential fields from reanalysis data. Each of the modes identified have strong spectral peaks in space-time spectra of dynamical fields, depending on the mode being analyzed. For example, the space-time spectrum of equatorial zonal wind at 50 hPa reveals strong eastward peaks at discrete zonal wavenumbers 1 through 4, having periods of around 14, 7, 4.7, and 3.5 days associated with four different scales of stratospheric Kelvin waves. These peaks lie along a 120m equivalent depth dispersion curve, as do the peaks of the equatorial meridional wind associated with the n=0 mixed Rossby-eastward inertio-gravity wave continuum of Matsuno’s theory. Similar strong peaks appear in zonal wind and geopotential associated with the first four meridional symmetric external Rossby modes, including the “5-day wave”. EOF analysis of filtered equatorial dynamical fields is a particularly effective method to isolate the equatorially-trapped modes, with filtered global data useful for the external modes. In all cases, the EOFs appear as “quadrature pairs”, each representing a propagating signal. The Principal Components (PCs) associated with each mode can then be used to establish its statistical structure by projecting global multilevel dynamical fields from reanalysis and satellite brightness temperature or precipitation onto the PCs in the time domain at lag. The square root of the squared sum of PC pairs also provides a convenient “activity index” for each of the modes. In this study, we relate the activity of the equatorially-trapped Matsuno and external Rossby modes to metrics of convective activity and to basic state circulation changes. It appears that the activity indices of many of the modes have strong peaks in the range of the Madden-Julian Oscillation (MJO), particularly during northern winter. Additionally, the well-documented variability of many of the modes associated with the stratospheric quasi-biennial oscillation (QBO) is also evident, as well as large variability at interannual and seasonal time scales. The leading Kelvin mode also displays a strong association with convectively-coupled Kelvin wave activity in the troposphere, again strongest during northern winter. This Kelvin mode is also apparently modulated by the El Nino-Southern Oscillation (ENSO), whereby changes in the basic state and perhaps the location of convective forcing lead to distinct changes in the vertical propagation characteristics and consequently result in longitudinal variations of Kelvin activity within the stratosphere. In all cases the stratospheric modes are also related to strong circulation signals in the troposphere all the way down to the surface.

• Title: Clouds and Climate: The Subtropical Cloud Transition
• Time: 13:30 - 14:30 on Sep. 29, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: The Intergovernmental Panel on Climate Change (IPCC) has reiterated that clouds remain the largest source of uncertainty in climate projections. Clouds in the atmospheric boundary layer, and in particular the subtropical cloud transition from stratocumulus to cumulus, appear to play a key role in cloud-climate feedbacks. Recent studies have highlighted the lack of complete understanding of this transition and the fact that climate models do not simulate the physics of the transition in a realistic manner. In this presentation, recent results on the characterization of the subtropical cloud transition using satellite observations illustrate its essential properties and the key questions remaining for a complete understanding of the transition. These observations together with Large-Eddy Simulations (LES) of the cloud transition are used to develop simple theories and a better understanding of the transition from a climate perspective.

• Title: Use of satellite observations to constrain parameterized cloud processes
• Time: 10:30 - 11:30 on Sep. 29, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: Clouds are to blame for much of our uncertainty about the effects of anthropogenic perturbations to the climate by aerosols and greenhouse gases. The difficulty in predicting cloud response to climatic perturbations arises from the small scales of the processes that govern clouds, which will be below the resolved scale of climate models for the foreseeable future. Climate models are therefore forced to parameterize the subgridscale processes. To produce high-confidence predictions of future climate, the parameterizations would ideally be both (1) physically motivated and (2) capable of correctly representing the present-day climate. Until the recent past, we could only crudely test whether models achieved the second goal because our knowledge of the present-day climate was severely limited. However, progress in remote sensing technology is giving us ever more insight into the climate system at the cloud process level. In models whose parameterizations are designed in analogy to known cloud-physical processes, novel satellite datasets are making it possible to test aspects of the parameterizations that strongly affect the most important climate model results. In this talk, we will illustrate this approach with applications to precipitation, lateral entrainment, and cloud-top entrainment, as a way to constrain model predictions of cloud feedback and effective radiative forcing by aerosol.

• Title: A climate modeling study on the mass loss of Antarctic ice sheet due to ice-ocean interaction
  (南極氷床質量損失に関する気候・氷床海洋間相互作用のモデリング研究)
• Time: 13:30 - 15:00 on Oct. 4, 2017.
• Place: General Research Bldg. 2F room 270.

• Title: Role of ocean carbon cycle in glacial reduction of atmospheric carbon dioxide concentration
  (氷期の大気中二酸化炭素濃度低下における海洋炭素循環の役割)
• Time: 13:30 - 15:00 on Sep. 28, 2017.
• Place: General Research Bldg. 2F room 270.

• Title: 高解像度大気数値モデルにおける急峻な山岳に対応する地形表現スキームの開発
• Time: 13:30 - 15:00 on Sep. 22, 2017.
• Place: General Research Bldg. 2F room 270.

• Title: TBD
• Time: 10:30 - 12:00 on Sep. 22, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: TBD

• Title: TBD
• Time: 13:30 - 15:00 on Sep. 21, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: TBD

• 場所: 総合研究棟　4センター共用2階会議室 270

• Title: How low can you go? Reducing the precision of data assimilation to improve forecast skill
• Time: 13:30 - 15:00 on Jul. 27, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: I will discuss the potential benefits of reducing precision within data assimilation. Data assimilation is inherently uncertain due to, for example, the use of noisy observations and imperfect models. Thus, rounding errors incurred from reducing precision may be within the tolerance of the system. Lower precision arithmetic is cheaper, and so by reducing precision in ensemble data assimilation, computational resources can be redistributed towards, for example, a larger ensemble size. I will present results using the Lorenz ’96 system and the ensemble square root filter. I use a reduced precision emulation tool to investigate how the performance of the system changes when reducing precision from double to half precision. By trading precision for ensemble size, the assimilation error can be reduced by 50%. I will illustrate how these results are sensitive to the length of the assimilation window. Additionally, I will present some results using the SPEEDY intermediate complexity GCM with a local ensemble transform Kalman filter. I will discuss challenges and opportunities for the use of half precision arithmetic and compare the impact of rounding and model errors.

• Title:CloudSat・CALIPSO衛星を用いた熱帯域に出現する対流雲の物理特性・微物理特性の解明
• Time: 13:30 - 15:00 on Jun. 30, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: 熱帯域に出現する対流雲は、全球の水循環および放射収支に対して重要な役割を果たす。特に、対流雲のコア部分から派生するアンビルはその光学的厚さや微物理特性によって地球の放射収支への影響が大きく変化する。またアンビルは水平に広く分布するため、対流雲全体の水平スケールのほとんどを決定する重要な因子である。しかし、海面水温や対流活動など環境場の変化に伴いアンビルの物理・微物理特性がどのように変化するかはあまり知られていない。そこで、本研究ではA-train衛星群に所属する能動型測器を搭載した CloudSat・CALIPSO衛星を用いて、アンビルを含めた対流雲の物理・微物理特性の実態把握および環境場依存性の解明を試みた。発表者は能動型測器データを利用した Cloud Object 解析手法を改良し、熱帯海洋上の対流雲特性について調査した。また、アンビルの水平・鉛直スケールおよび放射特性に影響を及ぼす雲粒有効半径や雲氷量などの微物理特性に着目し、対流雲内の雲微物理量の分布を明らかにした。本発表では、解析手法について説明を行い、光学的に薄いアンビルが対流雲全体の水平・鉛直スケールに及ぼす影響、および先に述べた対流雲特性の地域性についての結果を報告する。

• Title:
  話題1:地球システムの予測可能性− 10年規模気候予測を越えて
  話題2:北太平洋における気候と海洋生態系の関連性
  
• Time: 15:30 - 17:00 on Jun. 27, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract:
  話題1: 10年規模気候予測は、大気海洋力学の理解、最先端の気候モデル、及びデータ同化手法を集約させた革新的かつ挑戦的な研究課題である。その研究は、農業、林業、水資源、再生エネルギー、および環境変化といった、非常に多くの分野へと利用可能である。今回の発表では、最近の研究成果として、熱帯気候における数年間の予測可能性、アメリカ南西部における干ばつと森林火災の予測の２つの話題を紹介する。最初の話題では、 太平洋と大西洋間の相互作用を通したウォーカー循環の変調として特徴付けられる熱帯気候力学の新しい観点を紹介する。２つ目の話題では、地球システム予測システムを用いて、アメリカ南西部の干ばつと森林火災における数年規模の予測可能性について議論する。
  話題2: 太平洋十年規模振動(PDO)は北太平洋の海洋生態系変動に重要な役割を果たしている。例えば、過去のサケ漁獲量がPDOと連動している点は、気候と生態系の十年規模での関連性を示唆する。 一方で、アリューシャン低気圧の変動は、海洋生態系に短周期変動も引き起こす。このように短周期と長周期成分が混在するため、 気候に伴う生態系変動のメカニズムの解明を難しくさせている。この発表では、気候変動に伴った包括的な生態系メカニズムを提示し、生態系の長期メモリや生態系の予測可能性について議論する。また、過去５０年の海洋環境の復元から、モデルとデータを融合させた取り組みも紹介する。

• Title: Amundsen Sea simulation with optimized ocean, sea ice, and thermodynamic ice shelf model parameters
• Time: 15:00 - 16:30 on Jun. 1, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: Relatively warm ocean waters melt the ice shelves of the West Antarctic Ice Sheet (WAIS) in the Amundsen Sea (AS) and Bellingshausen Sea (BS), with consequences for global sea level rise and ocean circulation. Melt-induced ice shelves thinning weakens the buttressing of WAIS glaciers and increases the draw-dawn of ice into the ocean, contributing approximately 10% of the observed sea level rise between 2005 and 2010. Glacial melt water released from ice shelves in the AS and BS will freshen the shelf water locally as well as downstream in the Ross Sea (RS), which may lead to a change in the characteristics of Antarctic Bottom Water formed in the RS and thus influence the global thermohaline circulation. Good agreement between model results and observations are crucial for understanding and projecting these impacts on the current and future climate. Here, we conduct model optimization for a regional AS and BS configuration of the Massachusetts Institute of Technology general circulation model (MITgcm). In this presentation, I will show ongoing work from a model optimization using theadjoint method for a coarse-resolution AS configuration (~10 km horizontal grid spacing) and simulation results from a higher-resolution configuration (2 km grid spacing).

• Title: Level of Neutral Buoyancy, Deep Convective Outflow and Convective Core: New Perspectives Based on 5-Years of CloudSat Data
• Time: 13:30 - 15:00 on Jun. 1, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: An important aspect of the deep convection-to-outflow transition is the altitude where the outflow occurs, which can be conveniently summarized into a single parameter called level of neutral buoyancy (LNB). LNB is a critical parameter for understanding convection because it sets the potential vertical extent for convective development. This study develops a deeper and more complete characterization of LNB, deep convective outflow, and convective core, and the relationship between them. A proxy is also introduced to estimate convective entrainment. The principal findings are as follows: 1) Deep convection over the Warm Pool experiences larger entrainment dilution than that over tropical Africa. 2) The differences in convection internal vertical structure between tropical Africa and the Warm Pool suggest that deep convection over tropical Africa contains more intense cores. 3) Deep convective outflow occurs at a higher level when mid-troposphere is more humid and the convective system size is smaller. Convective system size is usually related to the life stage of convection (smaller at early stage). Hence, this result suggests that deep convection detrains at a greater altitude at early life stage.

• Title: Variability and changes in Northwest Pacific typhoon intensity
• Time: 15:00 - 16:30 on May. 19, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: While of great concern to East and Southeast Asian countries, variability and changes in typhoon intensity are poorly known owing to inconsistencies among different datasets. We have developed a new bias-corrected intensity dataset, and determined the dominant climatic factors that control the basin-integrated typhoon intensity over the past six decades. We find that upper ocean temperatures in the low-latitude Northwest Pacific and sea surface temperatures in the central equatorial Pacific control the seasonal average typhoon intensity by setting the rate and duration of typhoon intensification, respectively. An anomalously strong low-latitude Northwest Pacific upper ocean warming has favored increased intensification rates and led to unprecedentedly high average typhoon intensity during the recent global warming hiatus period, despite a reduction in intensification duration tied to the central equatorial Pacific surface cooling. We have further explored regional characteristics of typhoon intensity change since the late 1970s. Using cluster analysis, we show that typhoons that strike East and Southeast Asia have intensified by 12-15%, with the proportion of storms of categories 4 and 5 having doubled or even tripled. In contrast, typhoons that stay over the open ocean have experienced only modest changes. The increased intensity of landfalling typhoons is due to strengthened intensification rates, which in turn are tied to locally enhanced ocean surface warming on the rim of East and Southeast Asia. We will also discuss possible changes in both regional and basin-integrated typhoon intensity in a warming climate.

• Title: Exploring stochastic and multi-scale modeling approaches for a seamless prediction system
• Time: 13:30 - 15:00 on May. 19, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: Stochastic schemes to represent model uncertainty in the European Centre for Medium-Range Weather Forecasts (ECMWF) ensemble prediction system has helped improve its probabilistic forecast skill over the past decade by both improving its reliability and reducing the ensemble mean error. The largest uncertainties in the model arise from the model physics parameterisations. In the tropics, the parameterisation of moist convection presents a major challenge for the accurate prediction of weather and climate. Super-parameterisation is a promising recent alternative strategy for including the effects of moist convection through explicit turbulent fluxes calculated from a cloud-resolving model (CRM) embedded within a global climate model (GCM). These two approaches (stochastic and super-parameterisation) in convection parameterisation have emerged as new paths forward and complement the conventional approaches rather than replace them. We study the impact of these two approaches and a combination of the two on forecasts from weather to sub-seasonal and climate timescales. Results from the evaluation of model forecast skill and fidelity in the Tropics and for organized convective systems such as the MJO will be presented. We show that the combination of the two approaches helps improve reliability of forecasts of certain tropical phenomena, especially in regions that are affected by deep convective systems. This has implications on improving conventional convection parameterisation using hybrid approaches for probabilistic earth system forecasting as we await the exascale computing systems of the future to resolve convective processes in climate models.

• Title:衛星搭載降水レーダ群で降水気候解析に挑戦(中)
• Time: 13:30 - 15:00 on May. 12, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: 現在、地球上の降水やその性質には長期変化や変動があるのだろうか？ この疑問に答えるには、降水を正確に測る機器が全球を網羅し、かつ長期的に観測するデータが必要とされる。熱帯降雨観測衛星(TRMM)に搭載された降雨レーダ(PR)や全球降水計画(GPM)主衛星搭載の2周波降水レーダ(DPR)は、降水の立体観測から海陸を問わず高精度な降水量推定が可能なだけでなく、約20年の継続的な観測が行われ、衛星搭載降水レーダ群による長期観測は冒頭の問題に切り込むデータを蓄積しつつある。 しかしながら、降水の長期的な変動に由来すると思われる信号はセンサ特性の長期変化や運用の変遷由来の信号よりも圧倒的に小さい。そのため、PR/DPRの観測データを長期的に均一なデータとして再整備することが必要不可欠である。 発表者は降水の気候解析に適用可能なPR/DPR気候レコードを作成するために、 センサの運用変化やセンサ特性の長期変化を補正する手法開発を行ってきた。 本発表ではその開発の一端やその成果として整備されつつある気候レコードの利用可能性について報告する。

• Title: "A Letter from the Sky" - Atmospheric Tides and Tropical Convection
• Time: 13:30 - 15:00 on Apr. 28, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: Rainfall in the tropics exhibits a large, 12 h Sun-synchronous variation with coherent phase around the globe. A long-standing, but unproved, hypothesis for this phenomenon is excitation by the prominent 12 h atmospheric tide, which itself is significantly forced remotely by solar heating of the stratospheric ozone layer. We investigated the relative roles of large-scale tidal forcing and more local effects in accounting for the 12 h variation of tropical rainfall. A model of the atmosphere run with the diurnal cycle of solar heating artificially suppressed below the stratosphere still simulated a strong coherent 12 h rainfall variation, demonstrating that stratospherically forced atmospheric tide propagates downward to the troposphere and contributes to the organization of large-scale convection. The results have implications for theories of excitation of tropical atmospheric waves by moist convection, for the evaluation of climate models, and for explaining the recently discovered lunar tidal rainfall cycle.

• Title: 氷期氷床が大西洋子午面循環と気候に与える影響についての研究
• Time: 13:30 - 15:00 on Apr. 11, 2017.
• Place: General Research Bldg. 2F room 270.

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