過去のCCSRセミナー (2010年度)

＊下記のセミナーは中止いたしました。
2011年3月18日(金) 15:00 - 16:30
Michael A. Alexander (NOAA/Earth System Research Laboratory)

講演題目: The Influence of Air-Sea interaction in the North Pacific on ENSO
場所: 総合研究棟　4センター共用2階会議室 270
要旨: Previous studies suggest that the “seasonal footprinting mechanism” (SFM), in which fluctuations in the North Pacific Oscillation (NPO), a north south dipole in the sea level pressure pattern influence the ocean. NPO-related surface heat fluxes during winter drive subtropical SST anomalies in spring, which alter the atmosphere-ocean system over the tropics in the following summer, and can influence the development of ENSO events in the following fall and winter. Here, we test the SFM hypothesis by imposing NPO-related surface heat flux forcing in an atmospheric GCM coupled to a reduced gravity ocean model in the tropics and a slab ocean in the extratropics. The forcing is only imposed through the first winter and then the model is free to evolve through the following winter. The evolution of the coupled model response to the forcing is consistent with the SFM hypothesis: the NPO-driven surface fluxes cause positive SST anomalies to form in the central and eastern subtropics during winter; these anomalies propagate towards the equator along with westerly wind anomalies during spring and reach the equator in summer and then amplify, leading to an ENSO event in the following winter. The anomalies reach the equator through a combination of thermodynamically coupled air-sea interactions and equatorial ocean dynamics. The NPO forcing caused warming in the ENSO region in ~70% of the simulations. The impact of the forcing on individual events depends on the state of the tropical atmosphere-ocean system and the evolution of the feedback to the forcing, which has implications for both interannual and decadal variability throughout the Pacific. We will also examine whether the SFM and additional precursors to ENSO are apparent in CCSM4, NCAR’s recently released climate model.

＊下記のセミナーは中止いたしました。
2011年3月18日(金) 13:30 - 15:00
B.J. Sohn (School of Earth and Environmental Sciences Seoul National University, Seoul, Korea)

講演題目: Observational evidences supporting increased Walker circulation over the recent three decades Monsoon Precipitation Systems
場所: 総合研究棟　4センター共用2階会議室 270
要旨: In the modeling community, there has been a general agreement that the tropical Walker circulation has gone a weakening, in response to the global warming caused by anthropogenic emission of greenhouse gases. Furthermore it has been argued that the weakening will continue throughout the 21st century (e.g., Vecchi et al. 2006). Contradictory to such assertion, recent study by Sohn and Park (2010) showed that the Walker circulation intensity has been strengthened during the last three decades. This talk presents results from recent exploratory study using long-term observations to question whether strengthened Walker circulation is also visible in other observational data. Hypothesis is as follows. If there has been intensified Walker circulation over the tropics, the resultant changes may be detected in the deep convective clouds as well as in the upper tropospheric humidity (UTH) over the western Pacific warm pool region. At the same time the sea level pressure (SLP) gradient between the East Pacific and Western Pacific should be increased in response to the strengthened Walker circulation. It is shown that the long-term observations of deep convective clouds, UTH, and SLP all are much coherent with the hypothesized increased Walker circulation, strongly suggesting that the Walker circulation has been intensified in the last three decades. These are all appear to be associated with central Pacific warming and eastern Pacific cooling, supporting the dynamical coupling between the atmosphere and the tropical Pacific suggested by Cane et al. (1997) as an important delaying mechanism of the global warming.

＊下記のセミナーは中止いたしました。
2011年3月14日(月) 13:30 - 15:00
Weixin Xu (University of Utah, PhD student of Prof. Ed Zipser)

講演題目: Storm Morphology and Convection Occurrence of East Asian Monsoon Precipitation Systems
場所: 総合研究棟　4センター共用2階会議室 270
要旨: The East Asian Summer Monsoon (EASM) rainfall tends to be concentrated in rain belts that stretch for a few thousands of kilometers and affect China, Japan, Korea, and the surrounding areas. The monsoon rain belt produces not only widespread rain but also heavy rainfall, deep convection, and large convective mesoscale systems. These rainy and convective monsoon systems have significant impacts on both regional and global large scale circulations. Quantification of the monsoon convection and precipitation is required for many aspects such as model physical parameterization, evaluation of simulation statistics, rainfall retrievals, and weather forecasting. This study quantifies the populations, characteristics, and organizational structure of EASM cloud and rainfall systems using TRMM precipitation feature (PF) database. Convection occurrence, precipitation structures and storm morphologies were comprehensively analyzed for different weather regimes over East Asia. Storm morphologies of monsoonal precipitation systems were further compared with those of classic continental storms, oceanic systems, and monsoon systems in other parts of the world. Results show that convective properties of storms in the active Mei-Yu periods are significantly different those in the break periods or before the onset of the monsoon. It is further indicated that the EASM precipitation systems have convective properties, e.g., convection intensity or vertical precipitation structures of convective cores, sit in between those classic oceanic and continental regimes. The EASM storms are convectively weaker than storms of North American Monsoon or West African Monsoon, but relatively stronger than the Amazon rainy storms. These results based on TRMM “climatology” are also supported by in-situ observations from the 2008 field experiments in southwest Taiwan (TiMREX). TiMREX help to implement information on microphysical processes of Mei-Yu heavy precipitation systems.

＊下記のセミナーは中止いたしました。
2011年3月14日(月) 10:00 - 11:30
Dr. F Hugo Lambert (College of Engineering, Mathematics and Physical Sciences University of Exeter)

講演題目: Land-ocean surface temperature contrast and radiative forcing
場所: 総合研究棟　4センター共用2階会議室 270
要旨: Previous work has demonstrated that observed and modeled climates show a near time invariant ratio of mean land to mean ocean surface temperature change under transient and equilibrium global warming. We confirm this in a range of atmospheric models coupled to perturbed Sea Surface Temperatures (SSTs), slab (thermodynamics-only) oceans and a fully-coupled ocean. Away from equilibrium, we find that the atmospheric processes that maintain the ratio cause a land to ocean heat transport anomaly that we can approximate using a two-box energy balance model. When climate is forced by increasing atmospheric CO2 concentration, the heat transport anomaly moves heat from land to ocean, constraining the land to warm in step with the ocean surface, despite the small heat capacity of the land. The heat transport anomaly is strongly related to the top of atmosphere radiative flux imbalance, and hence tends to a small value as equilibrium is approached. In contrast, when climate is forced by prescribing changes in SSTs, the heat transport anomaly replaces "missing" radiative forcing over land by moving heat from ocean to land, warming the land surface. The heat transport anomaly remains substantial in steady-state. Our results are consistent with earlier studies that found that both land and ocean surface temperature changes may be approximated as local responses to global mean radiative forcing. The modeled heat transport anomaly has large impacts on surface heat fluxes, but small impacts on precipitation, circulation and cloud radiative forcing compared with the impacts of surface temperature change.

＊日程変更（2011/2/25）
2011年3月11日(金) 13:30 - 15:00
Dr. Christophe Sturm (ストックホルム大学）

講演題目: Atmospheric circulation indices reconstructed from water isotopes: toward a proxy 'assimilation'?
場所: 総合研究棟　4センター共用2階会議室 270
要旨: One critical issue in the current debate about future climate change is to distinguish between the response of the climate system to external (including anthropogenic) forcing and its stochastic variability. The study of past climate change provides evidence of forced response (e.g. orbital parameters, solar intensity, volcanic eruptions etc.) superimposed to intrinsic variability in the climate system. Yet before the instrumental period, paleoclimate variability needs to be reconstructed from proxy records, with inhenrent difficulties for their proper calibration and spatial representativeness. Climate models, in particular with embedded water isotope tracers, provide a useful tool to address these challenges. The present contribution focuses on 18O as a paleoclimate proxy, primarily in the hydrological cycle, as embedded tracer in regional and global climate models. Since the isotopic composition of precipitation is an integrative proxy of fractionation processes along an air parcel's trajectory, it is shown to be a robust proxy for atmospheric circulation variability. The present study, as a proof of concept, focuses on the reconstruction of the NAO index with an ERA40-nudged simulation (1959-2001) by REMOiso, combined with monthly d18O observations from the GNIP dataset. The non-linearity of the atmospheric circulation variability over the Atlantic across various (intra-seasonal to centennial) time-scales, and related challenges in describing it with linear eigenvalue techniques, is discussed in the perspective of the climate variability over the last Millennium. Finally, we apply this concept to the study of the Asian monsoon variability. We present preliminary results of the precipitation variability and related d18O composition in a GCMiso intercomparison study (SWING2) in the Asian monsoon region over the 1950-2000 period.

2011年3月8日(火) 15:00 - 16:30
Dr. Duane Waliser (Jet Propulsion Laboratory, California Institute of Technnology)

講演題目: The MJO: Some Updates on Science, Forecasting and Impacts
場所: 総合研究棟　4センター共用2階会議室 270
要旨: The Madden-Julian Oscillation is a dominant mode of tropical variability. It holds a unique place in the environmental forecasting problem by having a time scale that lies between the more traditional predictions associated with weather and climate. In this regard, it represents an important bridge in considerations of developing seamless predictions and for its unique applications to decision support. Considerable progress has been made in the last decade in the development of forecasting capabilities and in understanding the links between the MJO and its impacts and interactions with weather, climate and applications. This presentation will provide some updates in the areas of science, forecasting and impact studies associated with the MJO, with particular emphasis on activities associated with the WCRP-WWRP/THORPEX MJO Task Force and its predecessor, the US CLIVAR Working Group, and on studies that utilize satellite resources to advance MJO science and applications.

＊下記のセミナーはキャンセルとなりました。（2011/2/10）
2011年2月14日(月) 13:30 - 15:00
Dr. Yi Ming (NOAA/Geophysical Fluid Dynamics Laboratory)

講演題目: Aerosol-induced circulation changes
場所: 総合研究棟　4センター共用2階会議室 270
要旨: Unevenly distributed aerosols are thought of as more capable of altering regional climate than well-mixed greenhouse gases. With the help of global climate models, idealized models, theories and observations, I will discuss how two distinct climate regimes, namely the Tropics and boreal winter extratropics, may respond to anthropogenic aerosols both separately and collectively. The results reveal that local aerosol forcing has far-reaching effect on other parts of the global by modifying general circulation patterns, and could be key to attributing the observed 20th century variations in temperature and precipitation, especially on the regional scale.

2011年1月20日(木) 10:00 - 12:00
Dr. Pascal Yiou (LSCE/IPSL, France)

講演題目: Using analogues of atmospheric circulation for case studies and reconstructions
場所: 総合研究棟　4センター共用2階会議室 270
要旨: Circulation analogues have been used as a poor man's tool for meteorological statistical prediction. I will present of way of using this approach in a climatological context, with illustrations on recent climate extremes that occurred in Europe. This approach has allowed a description of the contribution of atmospheric variability in temperature or precipitation changes over the last decades. I will also present how this statistical tool can be used to reconstruct a three dimensional atmospheric field from surface observations. This is relevant for studies of climate of the last millennium, where several sea-level pressure data sets are available (from observations or GCM simulations) and could be used to force regional climate models.

2010年12月24日(金)・27（月） 13:00 - （予定）
修士論文直前発表会

場所: 総合研究棟　4センター共用2階会議室 270

＊下記のセミナー、時間が変更になりました。（2010/12/17）
2010年12月20日(月) 14:30 - 16:00
Prof. Gavin Schmidt (NASA)

講演題目: How can we enhance the relevance of palaeoclimate for assessing future climate change?
場所: 総合研究棟　4センター共用2階会議室 270
要旨: I will discuss the role of model/data comparisons for past climate changes and use of such comparisons for enhancing credibility in future projections. I outline a framework in which data synthesis combined with suitable modelling targets should be able to reduce uncertainty in both. By focusing on areas that the Intergovernmental Panel on Climate Change assessment report (IPCC AR4) highlighted as being particularly uncertain in future projections, or where current models produce a very wide range of responses, the relevance of paleo-climate data could be greatly enhanced. Specific targets include: the long-term behaviour of El Nino events and the potential response to volcanic and solar forcing; the variability of sub-tropical rainfall and the extent of the Hadley Circulation and their response to orbital and high-latitude forcing; ice sheet responses on sub-millennial timescales; multi-decadal changes in the North Atlantic ocean circulation and, certainly, overall climate sensitivity. In each case, I will highlight data synthesis steps and modelling approaches necessary for reducing the uncertainty.
Reference:
Schmidt, G.A, 2010: Enhancing the relevance of palaeoclimate model/data comparisons for assessments of future climate change. J. Quaternary Sci., 25, 79-87, doi:10.1002/jqs.1314. http://pubs.giss.nasa.gov/cgi-bin/abstract.cgi?id=sc02400t

2010年12月15日(水) 10:00 - 12:00
Dr. Jozef Syktus (Queensland Climate Change Centre of Excellence, Brisbane, Australia)

講演題目: Climate change and climate variability research at the Queensland Climate Change Centre of Excellence
場所: 総合研究棟　4センター共用2階会議室 270
要旨: This presentation will provide an overview of research projects undertaken at the Queensland Climate Change of Excellence in area of climate variability and climate change. The first part of the presentation will provide a brief introduction to QCCCE and describe the climate change issues facing Queensland. The second part of presentation will describe research results from recent projects undertaken by Climate System Research group at QCCCE. In particular the presentation will describe the results from the following research projects: a)Joint QCCCE/CSIRO modeling contribution to the 5th AR of the IPCC using the CSIRO Mk 3.6 climate model. b)Mid-Holocene and pre-industrial experiments comparison using CMIP5 results from CSIRO Mk3.6 model. c)Dynamical downscaling of climate change projections (CMIP5) using Conformal Cubic Atmosphere Model (CCAM) d)The impact of land cover change in Australia on regional climate, including changes in climate extremes and circulation e)Impact of stratospheric ozone depletion on the circulation changes over Southern Hemisphere. f)Projection of climate extremes including droughts using AR4 and CMIP5 climate model simulations.

＊下記のセミナー、日程が変更になりました。（2010/9/28）
2010年12月10日(金) 13:30 - 15:00
端野典平（東京大学大気海洋研究所）

講演題目: The Spectral Ice Habit Prediction System (SHIPS) -- a new approach to ice cloud microphysics for cloud resolving models
場所: 総合研究棟　4センター共用2階会議室 270
要旨: In the Earth’s atmosphere ice particles exist in various shapes and sizes, ranging from pole to equator. The ice particles play a significant role in the climate system as well as daily weather through radiative forcing and precipitation processes. The cloud resolving models (CRMs) have been successful in prediction of surface precipitation, but the comparison with satellite observations reveals a poor ability to depict radiative signatures of cloud systems. Prediction of the ice particles in CRMs faces challenges associated with the complexity of physical properties of ice particles: 1) some of the physical processes involving ice particles are still not well understood and 2) growth history of the ice particles that can be predicted with the conventional modeling approach is quite limited. In this talk, a new approach to overcome the above 2) is described and its ability is discussed. The new ice microphysical model is called the Spectral Ice Habit Prediction System (SHIPS), which represents a continuous property approach to microphysics simulation in a CRM. Each bin over a mass spectrum is characterized by a single representative ice crystal habit and type of solid hydrometeor. These characteristics are diagnosed based on a series of particle property variables (PPVs) of solid hydrometeors that reflect the history of microphysical processes and the mixing between bins and air parcels in space. Thus, SHIPS allows solid hydrometeors to evolve characteristics and size distribution based on their movement through a cloud. This is an approach in which a fundamental hypothesis or model of cloud microphysical process can be tested and studied in CRMs more vigorously than the conventional models.

2010年11月16日(火) 17:00 - 18:00
Prof. Sigfus J.Johnsen (Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Denmark)

講演題目: The Greenland ice cores; improved methods and some amazing results
場所: 大気海洋研究所２階講堂
要旨: My old teacher, Prof. Willi Dansgaard predicted in 1954 the possibility to study palaeo climates by measuring isotopes in ice cores. His group took over the isotope work on the Camp Century and the Byrd ice cores in 1968. The early results showed the cold last glacial period partly interrupted by several warm interstadials, also called the Dansgaard-Oeschger cycles. The Copenhagen group developed several important facilities including an isotope system doing 256 measurements per day in 1971, several shallow and deep ice core drills from 1975 and organizing deep ice core projects from 1979. This made the group a world leader in ice core research. Several new methods for obtaining and analyzing data from the Greenland ice cores have been applied over the past decade. The high res. chemistry data has allowed the North-GRIP core to be dated by counting annual cycles back to 60 ka BP (the GICC05 chronology). This effort will be continued even into the warm Eemian (interglacial) strata. Volcanic signals have been used to synchronize, with high precision, all of the Greenland deep ice cores and the Canadian Agassiz cores. Based on the isotopic signal and by using the small but stable Renland and Agassiz ice caps as reference, elevation changes during the Holocene have been derived for all the deep ice coring sites. The results are supported by the total gas content when available and suggest that the Greenland Ice Sheet (GIS) covered most of the continental shelf in the LGM. Furthermore, the elevation corrected ice core temperature signal reveals a strong climatic optimum for all the deep GIS cores. The isotope profile of the Camp Century core is consistent with over 600 m higher elevation in the CC region during the entire last glacial period. The new synchronization allows us to study gradients and local variability in the various proxies. Some of the results imply that winter precipitation was supplied by the split jet stream north of the Laurentide ice cap in the cold stadials. The high resolution deuterium excess signal from the North-GRIP core suggests that the atmospheric circulation in the North Atlantic region could be totally reorganized in a span of a few years. The rapid excess shift, found at the upper end of the Younger Dryas (GS1) strata, has been ratified by the Union of Geological Sciences as the Global Stratotype Section and Point (GSSP) for the Pleistocene-Holocene boundary. The stable isotope signal can be heavily smoothed by diffusion in the porous firn. Understanding the physics of this temperature dependent process allows us to reconstruct independent surface temperatures for strata deep in the ice. This new method uses spectral analysis of high resolution stable isotope data to quantify the degree of smoothing and thus the initial temperature. This new data, supports the palaeo temperatures based on borehole thermometry, yet another independent temperature reconstruction. It is also possible to undo part of the smoothing, that has changed an isotope profile. Results for annual isotope North-GRIP data from the LGM suggest extremely violent shifts in the position of the N- Atlantic polar front on time scales of 3 to 10 years.

2010年11月4日(木) 10:00 - 12:00
Dr. Pascal Yiou and Dr. Masa Kageyama (LSCE/IPSL, France, also at AORI from Nov.1)

講演題目: Extremes of European temperatures and the large-scale atmospheric circulation: a statistical point of view
要旨: The goal of the seminar is to identify research lines that could be developed during and after my stay at AORI and the University of Tokyo. In this presentation, I will present a few temperature events that struck Europe during the last decades. I will show the general connections with the general circulation and other climate variables. I will then detail some of the statistical analyses that have been made to quantify trends, and the links between large scale and local variables. I will conclude with working perspectives that could be extended to extreme events in eastern Asia.

講演題目: Climatic response to AMOC variations: timing and teleconnections. Some results from the IPSL model

場所: 総合研究棟　4センター共用2階会議室 270

2010年10月1日(金) 15:00 - 16:30
<博士論文予備審査会> 福田　悟（東京大学大気海洋研究所）

講演題目: 近紫外域の波長を利用した大気エアロゾルのリモートセンシング手法の研究
場所: 総合研究棟　4センター共用2階会議室 270
要旨:
大気エアロゾルは、雲形成や地球放射収支などに著しい影響を与える重要な大気組成物質である。その影響を定量化するためにエアロゾルの放射強制力が利用されているが、その評価には、IPCCの第４次報告書でも記述されているように、未だに大きな不確実性が残されている。これは全球の大気エアロゾルの分布が十分正確には評価されていないこと、また、その光学的特性や雲への影響が十分に理解されていないことに起因する。本研究では、近年になって使用されはじめた、近紫外域の波長(380nm)によるエアロゾルのリモートセンシング手法の開発をおこなった。本研究ではこのチャンネルを搭載しているGOSAT/ CAIおよびADEOS-II/GLI衛星搭載イメジャーのデータを利用した。　陸域におけるエアロゾル推定においては、地表面の反射率の大きさとその時空間的な変動の大きさが障害となるが、近紫外領域は、陸面の反射率が低いため,可視域などの波長に比べて有利であるといえる。このように陸域のエアロゾルリモートセンシングにおいては、地表面アルベドの推定が重要な点となるが、本研究ではGOSATの定常処理システム(DHF)で用いられているアルベド推定方法の改良をおこなった。このようにして得られたアルベドプロダクトから雲影除去や他のチャンネルの情報からアルベドを推定する修正カウフマン法を開発した。これらの手法を使って導出されたエアロゾルの光学的厚さを地上観測と比較したところ、陸域エアロゾルについて改善が見られた。

＊講演者の都合により、下記の講演はキャンセルとなりました。（2010/9/26）
2010年9月27日(月) 13:30 - 15:00
Dr. Wojciech W. Grabowski (Mesoscale and Microscale Meteorology Division, NCAR)

講演題目: Modeling of cloud-aerosol interactions
場所: 総合研究棟　4センター共用2階会議室 270
要旨: Cloud-aerosol interactions is a hot scientific topic, mostly because of postulated significant effects of nucleating aerosols (CCN and IN) on climate. Although these interactions have been recognized (and studied) by the cloud physics community for decades (for instance, in the context of weather modification), the literature related to the climatic implication of cloud-aerosol interactions is full of confusing concepts. In particular, there seems to be an apparent lack of recognition of the fact that observed correlation between clouds and aerosols (e.g., from satellite data) does not imply causality. This is because clouds and aerosols may co-vary according to the meteorology (i.e., correlation), but with only small effect of aerosol on cloud ensemble evolution. This is where numerical modeling can help when used appropriately. I will present results of numerical simulations that question postulated strong effects of CCN on deep convection. In the second part, I will shift to aerosol effects in shallow clouds, such as the tropical shallow convection and subtropical stratocumuls. A novel approach to simulate processing of CCN by such clouds, arguably essential in observed shallow subtropical cloud systems (pockets of open cells, or POCs, in particular) will be presented.

2010年9月24日(金) 16:00 - 17:30
Dr. K.V.S Badarinath (Atmospheric Science Section of National Remote Sensing Centre, India)

講演題目: Atmospheric aerosols and their influence on solar radiation - a study over tropical urban region using ground observations and satellite data
場所: 総合研究棟　4センター共用2階会議室 270

2010年9月16日(木)・17（金） 13:00 -
修士論文中間発表

場所: 総合研究棟　4センター共用2階会議室 270

2010年8月20日(金) 10:00 - 12:00
Dr. Nan Zhao and Dr. Yafei Wang (State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences)

講演題目: A Possible Theory for the Interaction between Convective Activities and Vortical Flows
要旨: Theoretical studies usually attribute convections to the developments of instabilities such as the static or symmetric instabilities of the basic flows. However, the following three facts make the validities of these basic theories doubtful. First, it seems in most cases the basic flow with balance property can not exist as the exact solution, so one can not propose appropriate problems of stability. Second, theories of dynamical instability are not able to describe a two-way interaction between convection and its background, because the basic states are prescribed in these issues. And, the third, the dynamical instability needs some extra initial disturbance to trigger it, which is usually another uncertainty. The present study suggests convective activities can be recognized in the perspective of its interaction with vortical flow. It is demonstrated that convective activities can be regarded as the superposition of free modes of convection and the response to the forcing induced by the imbalance of the unstably stratified vortical flow. Imbalanced vortical flow provides not only an initial condition from which unstable free modes of convection can develop but also a forcing on the convection. So convection is more appropriately to be regarded as a spontaneous phenomenon rather than a disturbance-triggered one that is indicated by any theory of dynamical instability. Meanwhile, convection, particularly the forced part, has also a reaction on the basic flow by preventing the imbalance of the vortical flow from further increase and maintaining approximately a balanced flow.

講演題目: The relationship between preceding ENSO and Asian summer monsoon
要旨: This paper examines the relationship between the East Asian summer monsoon and the El Nixio Southern Oscillation (ENSO) during the period from 1958 to 1998, which is quite different from the link between the South Asian summer monsoon and ENSO. Major findings are: (1) A new index, called the East Asian Monsoon Index (EAMI), is defined for measuring the East Asian monsoon, which could extensively describe the south-north distribution of the East Asian summer monsoon's activity. The interannual variability of the EAMI displays a significant negative correlation with the broad-scale Asian monsoon index proposed by Webster and Yang (1992) from 1976 to 1998. (2) A significant positive correlation between the summer 500 hPa geopotential height anomalies and the NINO-3 SST in the preceding fall and winter is found in the subtropical regions of East Asia and the western North Pacific, and in northeast Asia centered at 70°N, 137.5OE. A strong (weak) summer monsoon in the subtropical regions of East Asia tends to occur about two to three seasons after the NINO-3 SST anomalies exceed 1.5 C (drop below -0.7 C). (3) The above results suggest a delayed impact of the ENS0 on the East Asian summer atmosphere circulation. During the summer after the El Niiio reaches its mature phase, an anomalous blocking anticyclone tends to occur in northeast Asia. Meanwhile a subtropical high of the western North Pacific extends abnormally westward. This anomalous circulation pattern enhances the summer monsoon in subtropical East Asia. The abovementioned evolution of the circulation anomalies became more prominent in the unprecedented '97198 El Nixio event, suggesting that the devastating 1998 flood in southern central China may be partially due to the delayed impact of the '97198 El Nixio. The physical processes for the delayed impact besides the air-sea interaction in the tropical and subtropical western Pacific are discussed too.

場所: 総合研究棟　4センター共用2階会議室 270

2010年8月2日(月) 15:00 - 16:30
Dr. Toshihisa Matsui (NASA Goddard Space Flight Center)

講演題目: Multi-Sensor Satellite Simulators to Support Atmospheric Models and Satellite Missions
場所: 総合研究棟　4センター共用2階会議室 270
要旨: Variability of cloud-precipitation and aerosol processes affects the earth's energy and water budgets and, hence, atmospheric circulation. Different aspects of these macro- and micro-physical properties have been observed from a variety of satellite sensors in modern era, including A-train constellation satellites (e.g., Aqua, Aura, CloudSAT, CALIPSO, and PARASOL) as well as other single-platform multi-sensor satellites (e.g., TRMM and Terra). While a combination of multi-sensor satellite observations can provide a more complete view of cloud, precipitation, and aerosols, it is becoming a challenge for model and remote sensing communities to harness multi-sensor satellite observations through a set of the unified physics. A possible solution is to develop and utilize multi-sensor satellite simulators in order to translate the model simulation (geophysical parameter) space into the satellite-observation (radiance) space. To this end, Goddard Satellite Data Simulator Unit (SDSU) has been developed through multi-institutional collaborations. The SDSU is the end-to-end satellite simulator unit, which can compute satellite-consistent radiance or backscattering signals from the model-simulated atmosphere profiles and aerosol/condensate particles through passive microwave, radar, passive visible-IR, lidar, broadband, and ISCCP-like simulators. These simulated radiances and backscattering can be directly compared with the high-resolution satellite observations in order i) to establish the satellite radiance-based model evaluation framework, ii) to support satellite radiance-based data assimilation system, and iii) to provide a priori data files for development of multi-sensor satellite retrieval algorithms. In this seminar, I will highlight existing/potential applications of the Goddard SDSU related to the activities in the NASA centers, and address SDSU development strategy for future satellite missions: Global Precipitation Measurement (GPM), EarthCARE, and Aerosol-Cloud-Ecosystems (ACE) missions.

2010年7月16日(金) 13:30 - 14:30
大庭雅道（電中研）

講演題目: インド洋・太平洋の大気海洋相互作用がENSOの遷移の非対称性にもたらす影響
場所: 総合研究棟　4センター共用2階会議室 270
要旨: 熱帯太平洋上で発生するエルニーニョ・南方振動（ENSO）の遷移過程については、海洋波動の東西振動に基づく西太平洋振動子理論、および海洋貯熱量の南北輸送に重きを置く再充填振動子理論などの自励振動モデルが複数提案されてきた。これらのモデルは、ENSOの規則的な遷移を力学的に説明することに成功している。しかしながら、観測されたENSOの正（El Nino）と負（La Nina）の位相間の時間間隔を調べると、正位相から負位相への遷移は急速に進むのに対し、負位相から正位相への遷移は数年に渡って停滞する場合が多い。この遷移の非対称性は、従来の振動子理論では説明が困難とされていた。また、全球大気海洋結合モデルにおいても、ENSOイベントが線形的な振る舞いを示すため、発生頻度が高くなる傾向にあることが知られている。このようなENSOの遷移における非対称な振る舞いの原因として、太平洋以外からの外部強制、さらには熱帯積雲活動と海面水温との非線形的な関係が重要であると考えられるが、これらの点に注目した研究は少ない。そこで本研究では、インド洋を含む広域の熱帯域における気候変動モードに着目するとともに、海面水温偏差に対する熱帯対流活動の非線形的な応答がENSOの時間発展に対して及ぼす影響について数値モデルを用いて実験的に調べた。

2010年6月11日(金) 13:30 - 15:00
芳村圭（東京大学大気海洋研究所）

講演題目: Application of stable water isotopes on meteorology and climate sciences: Latest advancement of measurement and models for isotopes
場所: 総合研究棟　4センター共用2階会議室 270
要旨: The composition of stable water isotopes in precipitation and tropospheric water vapor is basically controlled by water's phase changes, so that the atmospheric processes associated with the water's phase changes may be deducible from the isotopic signals. For this reason, water isotopes are regarded as useful natural tracers of atmospheric hydrologic processes. Moreover, it is very important to fully understand the isotope cycle of the Earth to utilize isotopic information as climate proxies. However, just until recently the research community lacked sufficient observations and models for the isotopes, so that application for meteorological and climate studies had been limited. In this talk, I will explain the recent achievements on the isotope-incorporated AGCM (Yoshimura et al., 2008) and RCM (Yoshimura et al., 2010), and on the latest advanced measurement technique using FTIR instruments onboard satellite (Frankenberg et al., 2009) and ground-based observatories (Schneider et al., 2010). From these studies, the relationship between minute to interannual scale variations of the isotopes and cloud to global scale phenomena of the atmosphere were more understood. In the last part of the talk, I will briefly introduce my strategy for future research with the cooperation from other AORI members to apply the isotopic information for revealing unknown mechanism of meteorology and climate systems.

2010年6月10日(木) 14:00 - 16:00
Dr. Aixue Hu (NCAR)

講演題目1: Transient Response of the MOC and Climate to Potential Destabilization of the Land Ice in the Future
要旨: Multiple recent observations indicate an accelerated mass loss of the Greenland Ice Sheet, Western Antarctic Ice Sheet and glaciers around the world since late last century. This increased ice sheet mass loss might be evidence of global warming and could be related to elevated atmospheric greenhouse gas concentrations. Here, we use the National Center for Atmospheric Research Community Climate System Model version 3 to assess the potential influence of the mass loss of the land-based ice on the Atlantic meridional overturning circulation (MOC), the surface climate, and sea level in the next two centuries under the IPCC A1B scenario with prescribed rates of Ice Sheet melting. Results show that a low rate of Greenland melting will not significantly alter the MOC. However a moderate or high rate of Greenland melting does make the MOC weaken further. This further weakened MOC will not make the global climate in the next two centuries cooler than in the late 20^th century, but will lessen the warming, especially in the northern high latitudes. Moreover, the sea level changes due to steric effect and ocean dynamics could potentially aggravate the sea level problem near the northeast North America coast and the islands in the western Pacific region. The loss of the Western Antarctic Ice Sheet and the mountain ice caps and glaciers will not affect the MOC and the global mean temperature much. When all of the land ice sources are combined, the response of the MOC and global mean climate is similar as that of Greenland ice sheet melt alone. Therefore, the melting of the Greenland ice sheet has the most important impact on the MOC and surface climate.
講演題目2: Feedback between Bering Strait and Ice Age Climate Stability
要旨: Sea level fluctuations of about 20-30 meters occurred throughout the last glacial period. These fluctuations appear to have been derived primarily from changes in the volume of Northern Hemisphere ice sheets, and cannot be attributed solely to ice melt caused by varying solar radiation. Here we use a fully coupled climate model to show that the transport of relatively fresh Pacific water into the North Atlantic Ocean was limited when lower sea level restricted or closed the Bering Strait, resulting in saltier North Atlantic surface waters. This invigorated deep convection in the North Atlantic Ocean, strengthening meridional overturning circulation and northward heat transport in our model, which consequently promoted melting of ice sheets in North America and Europe. Our simulations show that the associated sea level rise led to a reopening of the Bering Strait; the flux of relatively fresh water into the North Atlantic muted meridional overturning circulation and lead to cooling and ice sheet advance in the Northern Hemisphere. We conclude that the repetition of this cycle could produce the sea level changes that have been observed throughout the last glacial cycle. Another great challenge in understanding the glacial-interglacial climate is to explain why frequent abrupt climate change events indentified from the Greenland Ice Core record occurred specifically during the period of 80 -- 11 thousand years (kyr) before present (BP), but almost no abrupt climate change events of the similar amplitude occurred during the Holocene and the period from the last interglacial to 80 kyr BP. Here we show, using a fully coupled state-of-art climate model, that it is the Bering Strait that has played a central role on these abrupt climate change events. A closed Bering Strait leads to a bi-stability of the ocean convey belt. The quick transitions from one stable state to the other result in the observed abrupt climate change.
場所: 総合研究棟　4センター共用2階会議室 270

2010年6月3日(木) 15:30 - 17:00
Prof. Fei-fei Jin (University of Hawaii, US) and Dr. Jong-Seong Kug (CORDI, Korea)

講演題目: Eddy-induced instability for low-freqeuncy varaibility

Dr. Jong-Seong Kug
講演題目: El Nino flavors and their implication on climate studies
場所: 総合研究棟　4センター共用2階会議室 270

2010年6月2日(水) 10:00 - 11:30
沢田雅洋（東北大学大学院理学研究科地球物理学専攻）

講演題目: Impacts of melting/evaporative cooling on tropical cyclone development and structure
場所: 総合研究棟　4センター共用2階会議室 270
要旨: A major energy source of tropical cyclone is condensational heating of water vapor associated with deep cumulus convection. Deep cumulus convection produces not only condensational heating but also diabatic cooling due to evaporation of rainwater and melting (and sublimation) of ice particles. These cooling strongly affect tropical cyclone development and structure (size and rainband). To clarify the roles of melting/evaporative cooling in tropical cyclone, cloud-resolving simulations are conducted under an idealized environment. Melting cooling weakens a secondary circulation of simulated tropical cyclone through radial pressure gradient force and it reduces inward transport of angular momentum, shrinking a TC size like radius of gale-force wind area. In contrast, evaporative cooling suppresses a rapid intensification but gradually enhances the secondary circulation, which increase the TC size. This result from strong diabatic heating outside of the eyewall associated with rainbands. For rainbands, evaporative cooling plays an essential role in its formation and propagation. These results reveal that impacts of evaporative cooling are significantly different from those of melting cooling.

2010年5月20日(木) 15:00 - 16:30
井口　享道（NASA Goddard Space Flight Center)

講演題目: Numerical experiment of C3VP2007 snowfall events using the WRF-SBM
場所: 総合研究棟　4センター共用2階会議室 270
要旨: The next-generation Global Precipitation Measurement (GPM) mission will offer a global view of precipitation systems including over middle and high latitudes and enable measurement of frozen precipitation and light rainfall, which are difficult to be observed by the Tropical Rainfall Measurement Mission (TRMM) sensors in operation. The development of retrieval algorithm for comprex precipitation systems is an important subject prior to the mission start. The project of a synthetic GPM simulator was proposed to offer a vitual cloud libraty (VCL) to support development of the retrieval algorithm. The VCL is composed of the prognostic variables in cloud resolving model simulation and the virtual sensor signal using a satellite simulator applied to the model output. The satellite retrieval algorithm can be cross-checked with a physical-based approach by using the VCL as a priori database. The first chapter of the GPM simulator project is planned for snowfall events during the Canadian CloudSAT/CALIPSO Validation Project (C3VP) field campaign. This campaign was took place at the site located between the Lakes Huron and Ontario in south central Ontario, Canada. We will introduce the current state of the simulation using the Weather and Research Forecasting (WRF) model with implemented the spectral bin microphysics for clouds (WRF-SBM) for snowfall events against the King-city C-band radar and aircraft CMRAD observations.

2010年5月14日(金) 13:30 - 15:00
久保川陽呂鎮（東京大学大気海洋研究所）

講演題目: 全球非静力学モデルNICAMを用いた対流圏界面領域における深い対流の役割に関する研究
場所: 総合研究棟　4センター共用2階会議室 270
要旨: 熱帯対流圏界面領域あるいは熱帯対流圏界層（Tropical Tropopause Layer, TTL）は、対流圏と成層圏の間の遷移層であり、対流圏の空気が成層圏へ流入する際の主たる入口である。成層圏オゾンに影響を与える物質のうち水蒸気は、空気塊がTTLを通過する際、TTL内の気温によってコントロールされている。TTL内の気温を決定する要因として、背の高い対流雲や、組織化した積雲群が励起する各種大気波動が議論されてきている。しかし、特に対流雲については、雲の中の気温や鉛直流を直接測定することが容易でないため、その役割の重要度に関して諸説があり決着がついていない。また、背の高い対流雲は、オゾンを減少させる触媒となる境界層内の物質を短時間に直接TTLや下部成層圏へ輸送する役割も担っているため、その地域性等を把握することは非常に重要である。そこで本研究では、地球シミュレーター上で動く全球非静力学モデルNonhydrostatic ICosahedral Atmospheric Model（NICAM）の出力データを用いて、TTLにおける深い対流と大気波動の気温変動に対する役割を調べた。NICAMは、全球モデルでありながら水平分解能は14～3.5 kmであるので、個々の積雲・積乱雲、組織化した積雲群、大規模スケールの大気波動等の間の相互作用が、現実的にシミュレートされていると期待される。解析には、ふたつの実験、全球が海で覆われた水惑星条件下で計算した実験（水惑星実験）と、現実的な海陸分布と初期条件を与え2006年12月15日－2007年1月15日の期間をシミュレートした実験（2006年12月実験）、からの出力データを使用した。水惑星実験の結果では、積乱雲は対流圏界面高度とTTL下端境界高度をそれぞれ赤道領域の0.14％、～25％の面積頻度でオーバーシュートしていた。10 m/sを超えるような強い鉛直流の頻度は、高度16 kmで急激に減少しており、これより上層は対流活動の直接の影響は弱い領域であることを示唆していた。対流圏界面付近の気温と水蒸気量の変動は、個々の積乱雲を現実的にシミュレートしたにも関わらず、組織化した積雲群から励起された赤道ケルビン波によって主に支配されていた。水平スケール1000 kmを越えるような大きな対流雲システムが見られたが、それがTTLの変動にもたらす影響は、ケルビン波に比べると小さかった。さらに、その影響は雲自身が与えているわけではなく、雲から励起された重力波によることがわかった。加えて、赤道ケルビン波の寒位相部上で、大振幅の重力波が観測され、これがモデル中で最も低温な領域のひとつとなっており、ケルビン波と重力波の重ねあわせがTTLにおける最も効果的な脱水プロセスのひとつとなりうることを示唆していた。

2010年4月23日(金) 13:30 - 15:00
平池友梨（東京大学大気海洋研究所）

講演題目: 南極中層水形成にかかわる氷縁域の表層水沈降を解明するモデル研究
場所: 総合研究棟　4センター共用2階会議室 270
要旨:
地球温暖化に代表される気候変動を知る上で，観測データの少ない南大洋で起こっている諸現象を解明することは非常に重要な研究課題である．本研究では, 海氷面と開水面に対する海面応力の違いによって生じ氷縁域(MIZ)で独特の物理現象であるEkman収束(ECMIZ)に注目した. このMIZでの海面応力差は海氷の空気に対する抵抗が開水面の大気に対する抵抗よりも大きいことにより生じることが知られているが, 先行研究は北半球に集中しており, 南半球の南極海で起こるECMIZを指摘した先行研究はない. 南極海は冬季に海氷が大きく張り出す季節海氷域である. 海氷の張り出しが最大になる冬季には, MIZはほぼ環状に存在し冬季に強まる強い偏西風帯付近に位置する. そのような風の場とMIZの関係から, ECMIZが起こると期待できる. さらに, MIZは渦による等密度面混合が活発であると考えられている南極周極流の南端に位置し, 海氷融解により表層塩分は低下する. 表層水の等密度面混合は, 南半球中層に分布する低塩低温の水塊である南極中層水(AAIW)形成プロセスの一つであると考えられている. このように, 西風, MIZと南極周極流の位置関係から, ECMIZにより沈降した表層水が渦による等密度面混合を経てAAIW形成に寄与しているものと考えることができる. また, 表層水の沈降は大気中の二酸化炭素吸収を見積もる際にも重要となる. 　以上のような観点から, 本研究では海氷海洋結合モデルを用いて, ECMIZの強さや分布を調べた. 実験に用いる大気データは, ECMIZの強さが西風の強さに大きく影響することから, 西風の年々変動を特徴づける大気大循環の主要モードである南半球環状モードの正(2001年, 西風強)と負(2000年, 西風弱)を考慮した. 実験の結果, 強いECMIZは, 2001年と2000年ともに7月から10月に大西洋域と太平洋域で海氷の融解を伴い, 高密度AAIWのoutcrop領域で起きていた. これらの領域では, MIZは西風の極大付近に位置していたために, 強いECMIZが引き起こされた. 一方, 背景の風が強い発散場であるインド洋では非常に弱かった. さらに, 環状モードの強い2001年の輸送量は環状モードの弱い2000年の1.4倍であり, どちらの年も大西洋の輸送量は太平洋の2倍であった. 　上記の実験は, 海洋表層の混合を一定として行った実験で, ECMIZの領域間の違いや年々変動を適切に表すことができた. 海洋混合層やMIZでの海氷の広がりをより良く表現するために, 結合モデルに混合層モデルを組み込み, 同様の実験を行った. 現実の海洋では, 表層の混合は鉛直シアや成層状態で決まり, 季節や領域など時空間的に変わる. また, 海氷の運動方向には海氷海洋間の摩擦の大きさとわずかな向きの違いが重要である. 海洋最上層流の表現は, 表層の混合(Ekman層厚)の変化による. 海洋混合層を組み込んだ実験では, 海氷分布の年々変動の再現性や海氷域の混合層が改善された. また, ECMIZの大きさは混合層モデルを組み込まない実験とほぼ同様の結果が得られた. さらに, 実験で得られた流速場や混合を用いて人工トレーサー実験をした結果, 観測されたCFC-11の分布と似た分布が得られた. 　本研究で明らかになったECMIZによる表層水の沈降は, 等密度面混合プロセスに基づいた考察を加えると, 太平洋AAIWよりも低温低塩な大西洋AAIWの形成に効果的であることが示唆された. すなわち, ECMIZが海氷の融解による低塩分の表層水を沈降させ, AAIW形成に重要な役割があると考えられる. よって本研究で明らかにされたECMIZでの表層水の沈降は, 将来の水塊形成や二酸化炭素吸収量変化の解明において重要であると示唆される.

2010年4月22日(木) 10:00 - 12:00
<博士論文予備審査会> Ohnmar Htway（東京大学大気海洋研究所）

講演題目: A study of climate system over Myanmar during the transition season to the summer monsoon
場所: 総合研究棟　4センター共用2階会議室 270
要旨:
Asian monsoon is a complex climate phenomenon involving many timescales of variations such as intraseasonal, interannual and decadal variations. This study emphasizes the interannual and intraseasonal variations of summer monsoon onset over Myanmar by using 33 years reanalysis data of ERA-40, NOAA-ERSST data, monsoon onset dates of Myanmar which are based on the station data and frequency and tracks of storms and depressions in the Bay of Bengal and the Andaman Sea data of DMH, Myanmar from 1968 to 2000. According to the composite analyses of precipitation, sea level pressure, 850 hPa and 200 hPa horizontal winds, the low pressure center in the northwestern part of India, the location of upper level anticyclone and low level westerly with continuous rain implies the intensification of local monsoon circulation over Myanmar. The analysis of composite sea surface temperature anomaly (hereafter SSTA) also indicates the important of April-May SSTA over the Nino-3(central-eastern Pacific) area and the western Indian Ocean to the early and late monsoon onset of Myanmar. The results of Fourier analysis are summarized as 30-60 day is a dominant periodicity of intraseasonal oscillation (ISO) during monsoon onset over Myanmar. The northward movements or standing oscillations of 30-60 day significant positive rainfall anomalies correspond to the early and late monsoon onset of Myanmar and the storm formation period can also be seen in the positive phase of this ISO. The temporal and spatial structures of rainfall anomaly also show that the maximum positive rainfall anomaly correspond with the movement of tropical disturbances from the Bay of Bengal to the north. There are seven cases of monsoon onset which advance towards Myanmar after the storm formation in the Bay of Bengal.

2010年4月9日(金) 13:30 - 15:00
Prof. Yuqing Wang (IPRC, University of Hawaii) and Kevin Hamilton (IPRC, University of Hawaii)

講演題目: Introduction of the IPRC
場所: 総合研究棟　4センター共用2階会議室 270

講演題目: Dynamical Downscaling of Western North Pacific Tropical Cyclone Genesis by the IPRC Regional Climate model
場所: 総合研究棟　4センター共用2階会議室 270
要旨:
Dynamical downscaling with a regional climate model (RCM) has been widely used for climate change assessment, seasonal predictions, understanding of climate processes and regional climate predictability (see the review by Wang et al. 2004). By this approach, a high-resolution limited area model is driven by relatively coarse resolution reanalysis or output of a coarse resolution global model to produce more detailed regional features. This has been approved to be particularly useful for the study of extreme climate events, including tropical cyclones. There have been several studies using RCMs to investigate the possible impact of global warming on the activity of tropical cyclones in different ocean basins. Knutson et al. (2007) demonstrated how well a nested regional atmospheric model driven by the reanalysis reproduced the recent multidecadal increase of Atlantic hurricane activity. However, the hurricane counts in the model were very sensitive to how strong the large-scale nudging in the interior of their model was.
In this talk, following a brief review in the dynamical downscaling of tropical cyclone genesis, the performance of the regional atmospheric model (IRAM) developed at the International Pacific Research Center (IPRC) in reproducing the tropical cyclone genesis over the Northwest Pacific has been evaluated. The NCEP/NCAR reanalysis is used to provide both initial and lateral boundary conditions to the IRAM, which was run at a horizontal resolution of 0.3° lat/lon. The weekly mean Reynolds SST was used as the lower boundary conditions for the model over the ocean. Simulations for 17 years from 1990 to 2006 are analyzed in the study. The model was initialized at June 1 and integrated continuously through November 30 for each year without the use of any interior nudging. The model TCs are located and tracked using an objective algorithm previously developed by Stowasser et al. (2007) for the IRAM. The results show that the model reproduced not only the mean seasonal cycle but also the interannual variability of tropical cyclones in the Northwest Pacific realistically. The correlation coefficients between the modeled and observed annual tropical cyclone counts and the power dissipation index reach 0.82 and 0.74, respectively. The correlation coefficient between the modeled and observed seasonal cycle reaches 0.92. Further, the model also reproduced the spatial distributions of genesis locations and frequency occurrence reasonably well. Further experiments for the Northwest Pacific TC genesis in response to sea surface temperature anomalies over the eastern Indian Ocean show that the model can reproduce the observed response quite well. Therefore, our results demonstrate that given accurate large-scale circulations by a coupled global model, the IRAM can be used to provide skillful dynamical downscaling for seasonal prediction and climate change projection of tropical cyclone genesis over the Northwest Pacific.

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