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: Modeling Microclimates and Projecting Climate Change in Hawaii
• Time: 13:30 - 15:00 on Apr. 10, 2015.
• Place: General Research Bldg. 2F room 270.
• Abstract: Hawaii is located in a dominant trade wind meteorological regime. The trade wind regime covers a very significant fraction of the globe, but few people live in this zone. The densely populated Hawaiian islands are a notable exception. While Hawaii is known for its pleasant weather, climate variations and climate change can present significant challenges to the residents. Sea level rise, beach erosion and threats to coral health are all familiar issues for the State. On the terrestrial side as well there are significant concerns including impacts of droughts on fresh water resources and impacts of global warming on plant and wildlife habitat. In this talk I will present some results from an ongoing initiative to project future climate changes in Hawaii using very fine resolution regional models. The interaction of the large scale flow with the very steep and fine scale topography on the main Hawaiian islands presents particular challenges, and I will discuss the current state of our simulations and our plans for future work at IPRC.

• Title: Assessing the Credibility of Dynamically-Downscaled Climate Projections
• Time: 13:30 - 15:00 on Mar. 25, 2015.
• Place: General Research Bldg. 2F room 270.
• Abstract: Last year, National Aeronautics and Space Administration (NASA) started a new project to assess the credibility of dynamically downscaled climate projections - taking results from global climate models (GCMs) or re-analysis to drive regional climate models (RCMs). These projections have been used for climate assessments, impact studies, and resource and management decision supports. Our goal is to establish a NASA framework for assessing the credibility of dynamically downscaled climate projections for the continental United States. Research will be done in collaboration with our interagency and international partners using NASA's unique high-resolution climate modeling, supercomputing, and big data analytic capabilities. In this talk, I will present an overview of the present progress and general perspective of this climate downscaling simulation project. This project is now in the pilot/scoping phase. So far we have completed 10-months pilot test runs using a regional climate model and started assessment of the simulation performance on the basis of the metrics analysis.

• Title: Nature Climate Change: How to get published
• Time: 15:00 - 16:30 on Feb. 25, 2015.
• Place: General Research Bldg. 2F room 270.
• Abstract: Nature Climate Change is a monthly journal dedicated to publishing the most significant and cutting-edge research on the science of climate change, its impacts and wider implications for the economy, society and policy. Senior Editor Bronwyn Wake will present information on journal formats and the publication process.

• Title: Sensitivity of Dense Shelf Water formation to buoyancy forcing and ice shelf basal melting
  Speaker: Eva Cougnon
  Title:Development of the Regional Ocean Modeling System (ROMS) for ice sheet/ocean interaction problems
  Speaker: Ben Galton-Fenzi
  
• Time: 13:30 - 15:00 on Feb. 10, 2015.
• Place: General Research Bldg. 2F room 270.

• Title: Toward Measuring Cloud Ice and Snowfall from Satellites
  
• Time: 13:30 - 15:00 on Feb. 6, 2015.
• Place: General Research Bldg. 2F room 270.
• Cloud ice and snow are important parameters in modulating global radiation balance and hydrological cycle. However, the ability of current NWP and GCM models in simulating these variables is very poor. Recent climate model validation studies showed that IPCC AR4/5 models cannot agree with each other even in the order of magnitude of the climatological mean cloud ice water path, although they produce similar amount of global mean rainfall, precipitable water and cloud fraction. A glare shortcoming in understanding the global distribution of cloud ice/snow and its radiative/hydrological effects is the lack of reliable global observation of these variables. Observations from several currently available satellites can potentially be used to retrieve cloud ice and/or snowfall, including radar and lidar observations from CloudSat and CALIPSO, and passive high-frequency microwave observations from GPM, NOAA, MetOP etc. satellites. However, cloud ice/snowfall retrieval algorithm development is still in its infancy; basic research on ice scattering and suitable inversion techniques is still greatly needed. In the past several years, we have been working in the area of developing retrieval algorithms of cloud ice and snow, and analyzing the characteristics of their mean states, spatial/temporal variations, and evaluating their radiative effects. In this talk, I will report the progress we have made in this research area, with emphases on the development of scattering models for nonspherical ice particles in microwave frequencies, understanding global cloud ice characteristics and its radiative forcing, and measuring snowfall by combining active and passive satellite observations.

• Title: Extratropical Air-Sea Interactions: Kuroshio Eddies, Pacific Storm Track and Climate Variability
• Time: 15:30 - 17:00 on Jan. 13, 2015.
• Place: General Research Bldg. 2F room 270.
• Abstract: Eddy-rich western boundary current regimes, such as the Kuroshio and Gulf Stream Extension regions, have been identified as key locations in the extratropics where SST variability may provide an important source of energy for driving atmospheric variability. In this talk, we present high-resolution regional climate modeling results, supported by observational analyses, that the rectified effects of meso-scale SST variability, largely confined in the Kuroshio-Oyashio confluence region (KOCR), can exert a significant remote influence on winter rainfall variability along the U. S. Northern Pacific coast. Warm ocean eddies punctuate atmospheric planetary boundary layer, moistening and destabilizing the lower atmosphere, which in turn affects the North Pacific storm track through impacts on cyclogenesis. We further show that the ocean mesoscale eddy atmosphere (OMEA) feedback plays an important role in maintaining the sharp SST gradient along the Kuroshio Extension. These findings point to the need to improve the representation of ocean mesoscale eddies and their interactions with the atmosphere in climate models.

• 場所: 総合研究棟　4センター共用2階会議室 270

• Title: Influence of the Gulf Stream on European wintertime blocking
  Speaker: Christopher H. O'Reilly
  Title: Diurnal precipitation and high cloud frequency variability over the Gulf Stream and over the Kuroshio
  Speaker: 見延庄士郎
  
• Time: 14:30 - 16:00 on Dec. 15, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: TBD

• Title: GRASP Algorithm: Application for enhanced retrieval of the aerosol properties from satellite observations
• Time: 13:30-15:00 on Dec. 9, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: The GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm has been developed for enhanced characterization of the properties of both aerosol and land surface from diverse remote sensing observations. The concept of the algorithm is described in details by Dubovik et al. (2014, ,2011). The algorithm is based on highly advanced statistically optimized fitting implemented as Multi-Term Least Square minimization (Dubovik, 2004) and deduces nearly 50 unknowns for each observed site. The algorithm derives a set of aerosol parameters similar to that derived by AERONET including detailed particle size distribution, the spectral dependence on the complex index of refraction and the fraction of non-spherical particles. The algorithm uses detailed aerosol and surface models and fully accounts for all multiple interactions of scattered solar light with aerosol, gases and the underlying surface. All calculations are done on-line without using traditional look-up tables. In addition, the algorithm can use the new multi-pixel concept - a simultaneous fitting of a large group of pixels with additional constraints limiting the time variability of surface properties and spatial variability of aerosol properties. This principle provides a possibility to improve retrieval for multiple observations even if the observations are not exactly co-incident or co-located. Significant efforts have been spent for optimization and speedup of the GRASP computer routine and retrievals from satellite observations. For example, the routine has been adapted for running at GPGPUs accelerators. Originally GRASP has been developed for POLDER/PARASOL multi-viewing imager and later adapted to a number of other satellite sensors such as MERIS at polar-orbiting platform and COCI/GOMS geostationary observat, Kluwer Academic Publishers, Dordrecht, Netherlands, 65-106, 2004.ions. The results of numerical tests and results of applications to real data (one year of PARASOL observation over Africa) will be presented.
  References
  Dubovik, O., T. Lapyonok, P. Litvinov, M. Herman, D. Fuertes, F. Ducos, A. Lopatin, A. Chaikov-sky, B. Torres, Y. Derimian, X. Huang, M. Aspetsberger, and C. Federspiel “GRASP: a versatile al-gorithm for characterizing the atmosphere”, SPIE: Newsroom, DOI:10.1117/2.1201408.005558, Published Online: September 19, 2014. http://spie.org/x109993.xml .
  Dubovik, O., M. Herman, A. Holdak, T. Lapyonok, D. Tanr, J. L. Deuz, F. Ducos, A. Sinyuk, and A. Lopatin, “Statistically optimized inversion algorithm for enhanced retrieval of aerosol properties from spectral multi-angle polarimetric satellite observations”, Atmos. Meas. Tech., 4, 975-1018, 2011.
  Dubovik, O., “Optimization of Numerical Inversion in Photopolarimetric Remote Sensing”, in Pho-topolarimetry in Remote Sensing (G. Videen, Y. Yatskiv and M. Mishchenko, Eds.)

• Title: TANSO-FTS/GOSATによる熱赤外スペクトルデータを用いた対流圏雲・黄砂・極域成層圏雲の観測
• Time: 16:00-17:30 on Oct. 17, 2014.
• Place: General Research Bldg. 2F room 270.

• Title:
  熱帯低気圧の暖気核に関する力学的研究(9:30-10:30 大野知紀)
  高解像度全球非静力学モデルにおける温暖化の熱帯低気圧への影響(10:30-11:30 山田洋平)
• Time: 9:30-11:30 on Oct. 8, 2014.
• Place: General Research Bldg. 3F room 320 (注：いつもと場所が違います）.

• 場所: 総合研究棟　4センター共用2階会議室 270

• Title:An evaluation of the direct aerosol radiative forcing from satellite remote sensing and climate modeling
• Time: 13:30-15:00 on Oct. 6, 2014.
• Place: General Research Bldg. 2F room 270.

• Title:Verification of the performance of the pseudo-global-warming method for future climate changes during June in East Asia
• Time: 15:00-16:30 on Oct. 1, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: The performance of the pseudo-global-warming downscaling (PGWDS) method is tested by comparison with the assumed true climate (ATC), which is a downscaling using a general circulation model (GCM) output data directly. The PGWDS is a simple way to downscale for a future climate using current weather data of a GCM added by the long-term mean difference between the present and the future climate projected by a GCM. The verification focuses on the East Asia during the rainy season of June. A significant change in the 30-year averaged monthly precipitation is found around the rain band in the future in both downscaling methods. Between the experiments of the PGWDS and the ATC, no significant differences in temperature and precipitation can be seen except for limited small areas. The findings indicate that the PGWDS has a highly potential to the reliable downscaling of the future climate. In smaller downscaling domains, however, the differences in precipitation increase remarkably near the upstream side of the lateral boundaries. The choice of the downscaling area is a critical issue for accuracy.

• Title:夏季の東アジア・北西太平洋上の降水と水輸送のシノプティックな変動に対する上部対流圏の影響 (Influence of upper tropospheric disturbances on the synoptic variability of precipitation and moisture transport over summertime East Asia and the northwestern Pacific)
• Time: 15:00-16:30 on Sep. 30, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: 本研究は，夏季の中国東岸域から北西太平洋にかけての降水と水蒸気輸送の総観 的な変動についての全般的な理解を深めることを目的に行った．衛星降水と客観 解析データを用いて，上部対流圏の渦位擾乱，降水量，下部対流圏の比湿の間に 明瞭な関係を見出した．40°N 付近で曲がりくねる 350 K 等温位面上の1.5 PVU 程度の渦位コンターの赤道側・低渦位側に沿って，幅数百km, 長さ千〜数千kmの 降水帯が頻繁に形成される．そこでは下部対流圏の比湿も増大し，同コンターを 境に北側では急落する．これに関わる総観的な状況には，いわゆるトラフの前面 での降水強化が含まれるが，それに限らない．結果はコンポジット解析によって も確認された． 境界の寄与を含む準地衡のポテンシャルエンストロフィーを用いた新しい診断 手法により，上述の領域の上部対流圏の擾乱はアジアジェットに沿って西から 伝播し，地表近くに強い強制をもたらすが，地表付近から上部対流圏の擾乱へ の上向き強制は弱いことが示せる．Qベクトル解析によると，降水帯での上昇流 は主に合流場により強制される．これに対応し，しばしば地表付近に前線が現 れる．また，上昇流は潜熱により強化される．水蒸気に富む気団の緯度分布の 変動は，この循環とともに，上層の変動に誘起される下層の流れによっても左 右される． 詳細はプレプリントをご覧ください： http://wwwoa.ees.hokudai.ac.jp/people/horinout/paper/horinouchi2014prepri_summersynop.pdf

• Title: Anelastic, pseudo-incompressible, and compressible simulation of moist atmospheric flows
• Time: 13:30-15:00 on Sep. 22, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: In this study, we compare anelastic, pseudo-incompressible, and compressible solutions to various moist atmospheric test problems across a wide range of spatial and temporal scales (thermals, flow over topography, deep convection, baroclinic waves). In the anelastic and pseudo-incompressible model, the pressure applied in the moist thermodynamics comes from either the environmental hydrostatically-balanced pressure profile in the standard model or is combined with nonhydrostatic perturbations from the elliptic pressure solver in the generalized model. The compressible model applies either an explicit acoustic-mode resolving scheme requiring short timesteps or a novel implicit scheme allowing timesteps as long as these used in the anelastic model. A unified numerical framework facilitates direct comparisons of results obtained with various versions of the model. The anelastic and compressible rising thermal solutions agree not only with each other, but also with previously-published compressible benchmark solution based on the comprehensive representation of moist dynamics and thermodynamics. Anelastic and compressible supercell solutions agree well for various versions of anelastic and compressible models even for cloud updrafts reaching 15% of the speed of sound. The nonhydrostatic pressure perturbations have a negligible impact on the moist dynamics. Numerical and physical details of the simulations, such as the advection scheme, spatial and temporal resolution, or parameters of the subgrid-scale turbulence, have a more significant effect on the solutions than the particular model applied. Differences between anelastic, pseudo-incompressible, and compressible moist baroclinic wave solutions are considered in the context of the past dry wave comparisons. The key conclusions of this investigation will be discussed at the seminar.

• Title: Is PW the PV of the tropics?
• Time: 13:30-15:00 on Sep. 8, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: For adiabatic balanced flow, potential vorticity (PV) is the master variable, a tracer governed only by advection which shapes the wind and mass fields diagnostically. Moist flow is more complex because condensation heating is hard to constrain. Maximizing conservation during derivations leads the inquirer to vertically integrated moist static energy. If temperature gradients are weak, this is closely related to column water vapor or "precipitable water" (PW). Animations show that PW behaves a lot like a horizontally advected tracer for days, while strongly shaping the condensation heating that governs the flow, albeit over time rather than instantaneously (diagnostically). A number of tropical situations will be shown in PW-centered views, and the implications for convection of the observed longevity of features in the PW field will be considered.

• Title: Statistical tool and its application on the field of hydrology
• Time: 16:00-17:30 on Aug. 5, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract:The application of statistical tools in the environmental science, engineers, biology and health science is being applied based on their research phenomena. In the field of statistical hydrology is a lesser known in the hydrological community. This presentation will address the suitability of statistical tools in the field of hydrology in particularly demonstrate a modelling technique. This study initiated to assess spatial and temporal variability of the hydrological time series in the South Australia. The temporal scale in minute, hours, daily and monthly rainfall, temperature, solar radiation, wind speed and runoff that was investigated for evidence of trends, seasonal effects, and extreme behaviour.

• Title: How well do the current state-of-the-art CMIP5 models characterise the climatology of the East Asian winter monsoon?
• Time: 16:00-17:30 on Jul. 25, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: Previous studies have revealed some common biases in coupled general circulation model’s simulations of the East Asian (EA) winter monsoon (EAWM), including colder surface air temperature and more winter precipitation over the EA region. In this study, we examined 41 fully coupled atmosphere-ocean models from CMIP5 (fifth phase of the Coupled Model Intercomparison Project), and address whether the current state-of-the-art CMIP5 models can characterise the climatology of the East Asian winter monsoon. We also compared the results with the models from CMIP3, which was extensively used in the fourth assessment report (AR4) of the IPCC. The results show that the cold surface air temperature (SAT) bias is lessened and the precipitation amount decreased with the current CMIP5 models. Moreover, the CMIP5 models perform better at predicting surface winds and high-level jet streams than the CMIP3 models. Moreover, CMIP5 models show more model consistency in most EAWM parameters, and the interannual variability of the SAT is closer to the observations. We also examined the EAWM-stratosphere coupling in the current models. Although the improvements are significant, deficiencies still exist in the simulation of the EAWM, e.g., the stronger EA major trough and the stronger zonal sea level pressure gradient and weak EAWM-stratosphere relation.
  Citation
  1. Wei, K., Ting Xu, Zhencai Du, Hainan Gong, Baohua Xie, 2013: How well do the current state-of-the-art CMIP5 models characterise the climatology of the East Asian winter monsoon? Climate Dynamics, DOI: 10.1007/s00382-013-1929-z.
  2. Gong H., L. Wang, W. Chen, R. Wu, K Wei, and X. Cui, 2013: The climatology and interannual variability of the East Asian winter monsoon in CMIP5 models, Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-13-00039.1
  3. Wei, K., and Q. Bao, 2012: Projections of the East Asian winter monsoon under the IPCC AR5 scenarios using a coupled model IAP_FGOALS. Adv. Atmos. Sci., 29(6): 1200-1213. Doi: 10.1007/s00376-012-1226-5.

• Title: Evaluation of climate models using satellite observations and implications for climate sensitivity
• Time: 16:00-17:30 on Jul. 22, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: Using NASA "A-Train" satellite observations, we evaluate the accuracy of cloud water content (CWC) and water vapor mixing ratio (H2O) outputs from ~20 climate models submitted to the CMIP5 and their post-CMIP5 developments. A quantitative scoring system is employed and a regime- dependent error diagnostics is performed. We found that the model spreads and their differences from the observations are much larger in the upper troposphere than in the lower or middle troposphere. Cloud parameterization errors contribute predominantly to the total errors for all models. Moreover, we show that the model performance in clouds and water vapor simulations are highly correlated with model estimates of climate sensitivity. The linkages between large-scale circulation and cloud distributions in present-day climate and under future climate change are explored.

• Title: Lunar gravitational atmospheric tide detected in the ERA Interim reanalysis data
• Time: 16:00-17:30 on July. 4, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: The lunar gravitational semidiurnal atmospheric tide is detected in the geopotential height field in the ERA-Interim reanalysis by regressing the data for each of the four daily analysis times onto the periodic lunar half-synodic cycle time series and high-pass filtering the obtained regression maps. A robust zonal wavenumber 2 pattern emerges, which agrees well with tidal theory and with previous studies based on station data in terms of its amplitude, its three-dimensional structure, and its seasonality at the Earth's surface. Above the 100 hPa level, the tidal signal amplifies with height and is downward propagating. Below that level it is nearly barotropic. Constructive (destructive) interference with the solar semidiurnal tide occurs 3 days before (after) the days of the full and new moon. The source of the lunar tide in the ERA Interim reanalysis and the role of the model in mediating its structure remains to be determined.

• Title: Influence of sudden stratospheric warming (SSW) in the tropical region: A case study of strong remote dynamical connection between polar and tropical region
• Time: 14:00-15:30 on Jun. 20, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: The talk is designed in two parts; first part will present the general features of temperature profiles globally in the height region of 1 to 40 km altitudes using COSMIC satellite observations over a period of 2007- 2011. Seasonal variability will be discussed that show the coldest region in stratosphere, in high latitudes (>60), exists between 10 km and 30 km altitudes during winter. Southern high latitude stratospheric region is found to be colder than northern latitude region. The next part of the talk will be focused on Sudden Stratospheric Warming (SSW) and its influence from polar to tropical region. Significant change in temperature observed in the stratosphere and tropopause region from pole to tropical region during a major SSW that occurred in Jan 2009. SSW event strongly modified the pattern of polar and tropical stratospheric circulation; after SSW a new pattern emerged that prevailed for ~ 2-3 months both in polar and tropical region. Stratospheric and tropospheric region have shown certain unique changes after the event, a clear descending cold phase at polar region seen which was located at altitudes similar to that of warming phase. During warm phase temperature rose to ~ 40°C in the polar region (80°N-90°N) (at altitudes >30 km) then it dropped down to - 80°C in the cold phase, which persisted for a longer duration. On the other hand, a new warm motion appeared over tropical region during the cold phase at polar region, which emerged after the SSW event. Strong implications of these unusually warm and cold phases are shown. The cold and warm phases altered significantly the tropopause temperature and its height. SSW also affected the tropical atmospheric stability. Cross equatorial response (from northern to southern hemisphere up to 30-40 S) due to SSW observed in the form of persisting anomalies in temperature.

• Title:
  (1) 陸域水循環に対する人為影響を考慮した渇水に関する温暖化影響評価 (佐藤雄亮)
  (2) Study on the economic damage due to pluvial flood in the world and impact of climate change (Rajan Bhattarai)
• Time: 14:00-16:00 on May 16, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract:
  (2) The assessment of flood risk and its future prediction under anthropogenic climate change are important to policy makers for future preparedness and adaptation planning. Almost all countries in the world including major cities suffer from flood damage every year due to large exposed population and property. The intensity of damage amount varies as per the level of their vulnerability. Flood losses are increasing more rapidly during late 20c and is expected to increase in future too. Another major factor contributes to future climate events like floods and its losses will be anthropogenic climate change. But due to lack of robust analytical framework to estimate future losses and lack of long term damage data; future projections of flood loss still have many uncertainties. Most studies regarding flood damage assessment have been done for river flood which always excludes pluvial flood damage usually caused by rainfall inside city area due to poor or insufficient drainage facilities. Also some extreme events corresponding to large return period is usually taken for damage assessments, which always exclude the damages caused by high frequency events, but reported as equal as extreme events. In this study, we present a robust methodology for pluvial flood damage assessment exclusively; taking all daily rainfall events into account and its application to future climate. We use recorded historical daily damage data in Japan that are archived in Ministry of Land, Infrastructure, Transport and Tourism (MLIT) of Government of Japan to produce functions namely damage occurrence probability function and damage cost function. Our statistical approach gives the probability of damage following every daily rainfall event and thereby the annual damage as a function of rainfall, population density, topographical slope, and gross domestic product. Our formulation of hazard, vulnerability and exposure will give a way to assess the pluvial flood damage in terms of its expected value in national, regional and global scale. We assess the pluvial flood damage amount for Japan in present and future climatic condition and giving a way to apply it for global scale and assess the pluvial flood damage in globe for present and future. Much details of each components of damage assessment and their results will be discussed in the presentation.

• Title: On how SSTs and regional circulation modulate Central American precipitation by means of its moisture sources
• Time: 15:30-17:00 on Apr. 25, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: An introduction to weather and climate research perspectives at the School of Physics and the Center for Geophysical Research of the University of Costa Rica will open this talk. Cen- tral America, located in a region featured by complex multi-scale interactions, among them, a belt of latent heat sources, strong easterly winds, the North Atlantic Subtropical High, the Western Hemisphere Warm Pool and the Inter Tropical Convergence Zone, surfaced as the most prominent tropical hot spot following results from future climate projections studies. The high sensitivity of this region to weather hazards, climate variability and its endangered ecosystems call our attention to the importance of understanding the regional hydrological cycle. To update our knowledge we need to overcome the poor performance of regional climate models to reproduce precipitation, biases in the reanalysis and satellite products as well as the scarcity of long term observations. The application of a Lagrangian back trajectories approach provided us with a new insight on moisture sources for Central America, gathering detailed information from available sources and heading us to improve our understanding on regional weather and climate. This talk is devoted to introduce the main climate features of Central America, focusing on regional precipitation patterns, the Caribbean Low Level Jet (CLLJ) and the Western Hemisphere Warm Pool (WHWP). The characterization of the moisture sources for Central America performed with the back tra- jectories analysis is presented. The relationships with the moisture sources and both the SST distribution and regional circulations are discussed in order to present some ideas on the role the WHWP and the CLLJ have in the modulation of regional precipitation.

• Title:The impact of tropical western Pacific convection on the North Pacific atmospheric circulation during the boreal winter
• Time: 15:00-16:00 on Apr. 18, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: In this study, we investigate the impact of atmospheric convection over the western tropical Pacific (100-145E, 0-20N) on the boreal winter North Pacific atmosphere flow by analyzing National Center for Environmental Prediction Reanalysis1, Extended Reconstructed Sea Surface Temperature and Global Precipitation Climatology Project data. The western tropical Pacific convection is not only the main energy source driving the local Hadley and Walker circulations, but it also significantly influences North Pacific circulation, by modifying a mid-latitude Jet stream through the connection with the local Hadley circulation. On the one hand, this strong convection leads to a northward expansion of local Hadley cells simultaneous with a northward movement of the western North Pacific jet because of the close correlation between the Jet and Hadley circulation boundaries. On the other hand, this strong convection also intensifies tropical Pacific Walker circulation, which reduces the eastern Pacific sea surface temperature, resembling a La Nina state through the enhanced equatorial upwelling. The cooling of the eastern tropical Pacific has an inter-tropical convergence zone located further north; thus, the local Hadley circulation moves northward. As a result, the jet axis over the eastern North Pacific, which also corresponds to the boundary of the local Hadley circulation, moves to higher latitude. Consequently, this northward movement of the Jet axis over the North Pacific is reflected as a northwest-southeast dipole sea level pressure (SLP) pattern. The composite analysis of SLP over the North Pacific against the omega (X) (Pa/s) at 500 hPa over the western tropical Pacific actually reveals that this northwest-southeast dipole structure is attributed to the intensified tropical western Pacific convection, which pushes the Pacific Jet to the north. Finally we also analyzed south Pacific for the austral winter as did previously to North Pacific, and found that the results were consistent.

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