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: 南極昭和基地大型大気レーダーによる観測と中層大気NICAMによる再現実験
• Time: 15:00 - 16:30 on Mar. 24, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: 南極昭和基地大型大気レーダー（PANSYレーダー）は対流圏から中間圏までの3次元風速を高分解能・高精度で連続観測することができる大気レーダーである。PANSYレーダーは2011年に昭和基地に設置され、調整しながら2012年4月より部分システムによる連続観測を行ってきたが、2015年3月16〜24日にフルシステム観測に成功した。このフルシステム観測期間に生じた顕著な太陽フレアイベントに関連すると考えられる強い中間圏エコーが受信された。観測で得られた風速を調べてみると、周期約12時間程度の振幅の大きな波状擾乱が出現していたことがわかった。高度90kmから120km付近に観測される極域中間圏における約12時間周期の波動擾乱の存在自体は多くの先行研究により指摘されており、潮汐波や、潮汐波と惑星波の非線形相互作用によって生じる東西波数1や3の波によると考えられている。しかし、PANSYレーダーが擾乱を観測した高度領域は70km付近である。この擾乱の水平構造を調べるため、モデルトップを中間圏に拡張した非静力学正二十面体モデル（NICAM）を用いた再現実験を行った。水平格子には、Shibuya et al. (2016)で考案した極域において一様等方な格子構造を持つ伸縮格子を用いた。解析の結果、この擾乱は惑星スケールの潮汐波ではなく水平波長1500km以上の慣性重力波によるものであったことが分かった。この慣性重力波の発生と伝播について詳しく調べたところ、対流圏界面付近の中緯度ジェットの自発的調節過程によって発生した波束が中間圏まで伝播した可能性が示唆された。また、成層圏の極渦付近において発生した波束も確認された。PANSYレーダーフルシステム観測は2015年10月1日〜2016年9月30日の1年間にノンストップで行われている。この期間の中層大気NICAMを用いた再現実験も現在行っており、その結果についても示す予定である。

• Title: The energetics of Southern Ocean upwelling
• Time: 14:00 - 15:30 on Mar. 15, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: The ocean's meridional overturning circulation is closed by upwelling of dense, carbon-rich waters to the surface of the Southern Ocean. It has been proposed that upwelling in this region is driven by strong westerly winds, implying that the intensification of Southern Ocean winds in recent decades may have enhanced the rate of upwelling, potentially affecting the global overturning circulation. However, there is no consensus on the sensitivity of upwelling to winds, nor the nature of the connection between Southern Ocean processes and the global overturning circulation. In this talk I will discuss the sensitivity of the overturning circulation to changes in Southern Ocean westerly wind stress using an eddy-permitting ocean-sea ice model. In addition to a suite of standard circulation metrics, an energy analysis is used to aid dynamical interpretation of the model response. Increased Southern Ocean wind stress enhances the upper cell of the overturning circulation though creation of available potential energy in the Southern Hemisphere, associated with stronger upwelling of deep water. Poleward shifts in the Southern Ocean westerlies leads to a complicated transient response, with the formation of bottom water induced by increased polynya activity in the Weddell Sea and a weakening of the upper overturning cell in the Northern Hemisphere. The energetic consequences of the upper overturning cell response indicates an interhemispheric connection to the input of available potential energy in the Northern Hemisphere.

• Title: マッデン=ジュリアン振動(MJO)相空間上における予報精度の評価と予測可能性推定
• Time: 13:30 - 15:00 on Mar. 14, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: セミナーの前半では，マッデン・ジュリアン振動(MJO)相空間上での予報精度の指標について話す．これまで二変数二乗平均平方誤差(RMSE)と二変数アノマリ相関係数(ACC)の組み合わせが慣例的に使われてきたが，これらの評価方法はMJOイベントに関するモデルバイアスを評価できない．それだけでなく，ACCはMJOの振幅に強く依存するので，あるフェーズでMJOのシグナルが減衰する傾向にあるモデルにおいてACCを使うことは適切ではない．平均誤差ベクトルはモデルの平均移動速度誤差とRMSEを結びつけることでこの問題を解決する．ここでは気象庁の一か月予報モデルに適用した結果をまじえて，上記の検討結果を紹介する． 後半では，潜在的な予測可能性の代替的な推定手法を提案する．先行研究において広く採用されているアンサンブルスプレッドを用いた手法は完全モデルの仮定を前提としており，全球気候モデル(GCM)によるMJOの再現が不完全な現状においては信頼できる推定値を与えるとは限らない．そこでスプレッドの代わりに，位相空間内における近傍予報群を対象とした観測値とアンサンブル平均予報の間の相関係数から得られる不確実性の指標を用いることを提案する．ここでACC不確実性と呼ぶことにする新たな指標は，一つのGCMだけでなく，複数モデルのアンサンブル平均に対しても算出することが可能である．ここでは新たな手法の紹介とともに，Subseasonal to seasonal (S2S) prediction projectの一環として収集された三局のGCMによる複数モデルアンサンブル予報に適用した結果について報告する．

• Title: Asymmetrical transition of El Nino and La Nina: mechanism and future change
• Time: 15:30 - 17:00 on Feb. 17, 2017.
• Place: General Research Bldg. 2F room 270.

• Title: 惑星中層大気の雲層加熱で生じる大循環の力学
• Time: 13:30 - 15:00 on Feb. 13, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: 金星やタイタンでは全球を雲やエアロゾルが覆い，その微粒子による太陽光加熱が中層大気大循環を駆動する．しかしながら，このような惑星大気 大循環の力学は十分に理解されていない．Yamamoto and Takahashi (2016)では，金星GCMの長時間積分の相互比較で用いた簡略化モデル（放射強制 を帯状平均南北温度差とニュートン冷却で表現したモデル）の自転周期を変えた実験を行った．自転周期が１日だと南北方向に多重セル構造が出現 し，自転周期を16日にすると赤道対称の単一セルになる．さらに自転を極端に遅くすると（243日周期），ジェットが高緯度に形成され，その ジェットの傾圧不安定の極向き渦熱輸送による間接循環が極域で出現し，自転が遅いにも関わらず多重セル構造となる．子午面循環と赤道向きの運 動量輸送による超回転形成機構が機能している中，上記の極向き渦熱輸送による鉛直EPフラックスが高緯度ジェットを弱めると，赤道域の風速も減 少し，超回転が十分に発達しない．これまで重視されていた潮汐波や順圧波に加えて，高緯度の傾圧不安定による混合ロスビー重力波と間接循環の 有無が超回転強度に影響を与える．本セミナーでは，様々な天文パラメーターに対する惑星中層大気大循環構造について概観した後，放射伝達ス キームや地形を組み込んだ金星GCM(池田2011)を用いて，現実に近い条件でシミュレーションされた大循環および波動構造について報告する．

• Title: Common model biases may reduce CMIP5's ability to simulate the recent Pacific La Nina-like cooling
• Time: 16:00 - 17:30 on Jan. 27, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract: Over the recent three decades sea surface temperate (SST) in the eastern equatorial Pacific has decreased, which helps reduce the rate of global warming. However, most CMIP5 model simulations with historical radiative forcing do not reproduce this Pacific La Nia-like cooling. Based on the assumption of “perfect” models, previous studies have suggested that errors in simulated internal climate variations and/or external radiative forcing may cause the discrepancy between the multi-model simulations and the observation. But the exact causes remain unclear. Recent studies have suggested that observed SST warming in the other two ocean basins in past decades and the thermostat mechanism in the Pacific in response to increased radiative forcing may also play an important role in driving this La Nia-like cooling. Here, we investigate an alternative hypothesis that common biases of current state-of-the-art climate models may deteriorate the models' ability and can also contribute to this multi-model simulations-observation discrepancy. Our results suggest that underestimated inter-basin warming contrast across the three tropical oceans, overestimated surface net heat flux and underestimated local SST-cloud negative feedback in the equatorial Pacific may favor an El Nio-like warming bias in the models. Effects of the three common model biases do not cancel one another and jointly explain ~50% of the total variance of the discrepancies between the observation and individual models' ensemble mean simulations of the Pacific SST trend. Further efforts on reducing common model biases could help improve simulations of the externally forced climate trends and the multi-decadal climate fluctuations.

• Title:
  Impurities of glacier ice: accumulation, transport and albedo (Thomas Goelles)
  InitMIP-Greenland experiments with the ice sheet model SICOPOLIS(Ralf Greve)
• Time: 13:30 - 14:30 on Jan. 27, 2017.
• Place: General Research Bldg. 2F room 270.
• Abstract(Thomas Goelles): Albedo is a major control of surface melt and has decreased over the entire Greenland ice sheet, especially at lower elevations near the margin where glacier ice is exposed for part of each year. The albedos of ice and snow are lowered by dark impurities such as mineral dust and black carbon, a by-product of combustion. Current sea-level projections rarely include albedo as a dynamic model component. In models which consider albedo, snow albedo is often treated with sophisticated methods, while ice albedo is still treated as a constant. I will present a model framework which includes a dynamic ice albedo component. Tests of the model on data of the western margin of the Greenland ice sheet show that the model is capable to match the albedo over several years. Simplified expermiments showed that impurities have a higher effect on sea level rise under warmer conditions, due to a feedback between impurity accumulation and surface melt.
  Abstract(Ralf Greve): The Ice Sheet Modeling Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project Phase 6 (CMIP6) focusing on the Greenland and Antarctic ice sheets. In order to compare and evaluate the initialisation methods used in the ice sheet modelling community and estimate the uncertainty associated with initialisation, the ice sheet model initialisation experiments for Greenland (InitMIP-Greenland) were devised as an early sub-project within ISMIP6. We contribute to InitMIP-Greenland with the ice sheet model SICOPOLIS and two different spin-up techniques (fixed-topography vs. freely-evolving-topography approach). Results show that the influence of these different spin-ups on the evolution of the ice sheet in the future is pronounced.

• 場所: 総合研究棟　4センター共用2階会議室 270

• Title: The initiation and intensification of the Madden-Julian Oscillation in recent field campaigns
• Time: 13:30 - 15:00 on Dec. 22, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: In the recent studies of the Madden-Julian Oscillation (MJO), the multi-scale nature and its diversity receive increasing attention. Detailed case studies are useful to deal with these research topics. In this seminar, the initiation and intensification process of the MJO events that occurred during the CINDY2011/DYNAMO (October 2011-January 2012) and Pre-YMC (November-December 2015) field campaigns led by the JAMSTEC research group are discussed. In the CINDY2011/DYNAMO period, robust MJO event were initiated in mid-October and mid-November in the western Indian Ocean. In both MJO events, the increase in precipitable water started 8-9 days prior to the convective initiation. The moisture budget analysis over the equatorial Indian Ocean reveled that advection of basic moisture by intraseasonal easterly anomalies and of intraseasonal moisture anomalies by the basic zonal wind were pronounced in these two events. The nonlinear high-frequency terms in the meridional moisture advection were the same order of magnitude as the primary term in the middle troposphere, implying systematic upscale transport of moisture. In the Pre-YMC period, an abrupt intensification of MJO event occurred over the Maritime Continent (MC) in mid-December. The morphology and propagation of the convective systems were drastically altered at the onset of the MJO. The onset was preceded by strong northwesterly along the west coast of Sumatra associated with a synoptic-scale rotational disturbance, and enhancement of diurnal precipitation. Moisture budget analysis using the global 7-km mesh Nonhydrostatic Icosahedral Atmospheric Model (NICAM) forecasts indicated middle tropospheric moistening associated with the northwesterly. Further investigation on the roles of the diurnal convection and equatorial wave disturbances in the initiation of the MJO is underway. A research plan for the forthcoming field campaign the Years of the Maritime Continent (YMC; 2017-2019) will be also introduced.

• Title: Insights into the physics of the Madden-Julian Oscillation from superparameterized climate simulation
• Time: 10:30 - 12:00 on Dec. 6, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: The SuperParameterized Community Atmosphere Model (SPCAM) generates a convincing Madden-Julian Oscillation signal while making minimal assumptions about moist convection. Combined with its computational efficiency relative to fully global cloud resolving models, this has made it an attractive tool for MJO hypothesis testing in recent years. This talk synthesizes several recent studies using SPCAM as a tool to better understand the physics of the MJO. First, I will test the role of the Indian Ocean Dipole in regulating the initiation and propagation dynamics of the MJO, suggesting ENSO is more critical via its indirect link to the IOD. Then, I will argue that mesoscale organization is not critical to SPCAM’s MJO signal by artificially restricting the room available in its embedded cloud resolving arrays. Next, I will argue by artificially modulating the rate at which tropical vorticity anomalies advect moisture advection that this process plays a causative role in MJO propagation, in line with a moisture mode view. Finally, I will show competing results that challenge a moisture mode view in idealized simulations that use constant SSTs and extreme climate variation. This achieves an MJO-like signal co-existing in an unusual basic state that is difficult to reconcile with advective propagation. In the process, a “cold MJO” is discovered, as well as smooth variations of MJO size, speed and amplitude in association with climate change across a wide SST range.
  References:
  M. S. Pritchard and D. Yang, 2016. Response of the superparameterized Madden-Julian Oscillation to extreme climate and basic state variation challenges a moisture mode view. J. Climate, 29, 4995-5008, http://dx.doi.org/10.1175/JCLI-D-15-0790.1.
  Benedict, J. J., M. S. Pritchard, and W. D. Collins, 2015. Sensitivity of MJO propagation to a robust positive Indian Ocean dipole event in the superparameterized CAM, J. Adv. Model. Earth Syst., 7, 1901-1917, doi:10.1002/2015MS000530.
  Pritchard M. S., C. DeMott and C. S. Bretherton, 2014. Restricting 32-128 km horizontal scales hardly affects the MJO in the Superparameterized Community Atmosphere Model v.3.0 but the number of cloud-resolving grid columns constrains vertical mixing, J. Adv. Model. Earth Syst., 06, doi:10.1002/2014MS000340.
  Pritchard, M. S. and C. S. Bretherton, 2014. Causal evidence that rotational moisture advection is critical to the superparameterized Madden-Julian Oscillation, Journal of the Atmospheric Sciences, 71(2) 800-815, doi:10.1175/JAS-D-13-0119.1

• Title:Summary of findings made by GOSAT and Current Status of GOSAT-2 Project
• Time: 13:30 - 15:00 on Dec. 2, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: GOSAT (Greenhouse gases Observing Satellite) is a joint mission of Ministry of the Environment (MOE), National Institute for Environmental Studies (NIES), and Japan Aerospace eXploration Agency JAXA). It is the world’s first satellite dedicated to greenhouse gas monitoring from space, and was successfully launched on January 23, 2009. Although it has finished its nominal operation period (5 years) in January 2014 and is currently in the extended operation period, it has still been monitoring the Earth’s atmosphere continuously. The data have been widely used not only for source/sink inversion of carbon dioxide (CO2) and methane (CH4) in global scale but also for assessing regional emission sources of the gases. One of the most conspicuous results is the detection of Sun-Induced chlorophyll Fluorescence (SIF) signals by the main sensor, Thermal And Near- infrared Sensor for carbon Observation - Fourier Transform Spectrometer (TANSO-FTS), to estimate the Gross Primary Production (GPP) of biosphere. SIF data has been originally used to evaluate the declination of activity of plants caused by physiological stresses such as water stresses rather than to estimate GPP directly. Therefore, it is expected that more precise estimation of GPP by combining SIF data with Photochemical Reflectance Index (PRI) and Water Stress Trend (WST) which represent physiological stresses, and can be measured by a future Japanese satellite such as Global Change Observation Mission- Cimate 1 (GCOM-C1). Another important activity is "GOSAT Air Pollution Watch", which is being designed for rapid processing / distribution of GOSAT TANSO-Cloud and Aerosol Imager (TANSO-CAI) data for monitoring of air pollution caused mainly by particulate matters such as PM2.5 and Black Carbon (BC). Its testbed is already developed and basic performances have been demonstrated using TANSO-CAI data. Data processing algorithms in GOSAT Air Pollution Watch are based on but modified from GOSAT/GOSAT-2 algorithms for aerosol product generation to realize faster and timely data processing. Data from GOSAT Air Pollution Watch will be used to inform the current distribution of the polluted air. In addition, they will contribute to short term prediction of air pollution using atmospheric transport models. The successor, GOSAT-2, will be launched in FY2017. Most of the design reviews for spacecraft, instruments, and ground data processing systems have been finished. The main sensor of GOSAT-2, TANSO-FTS-2 is designed based on CrIS (Cross-track Infrared Sounder) onboard NASA’s Suomi NPP for gas sounding. It has a widened band in a short wavelength infrared region to detect carbon monoxide (CO). Intelligent pointing system, which is a dynamical system for targeting at selected clear sky scenes has been newly developed. It is expected that the detectability of clear sky scenes become larger twice or more compared with the current system.

• Title: Strategy to exploit satellite observations for evaluating large-scale and convective-scale updraft profiles
• Time: 13:30 - 15:00 on Nov. 17, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: Among the crucial problems involved in the tropical energy budget are the thermodynamic effects of an ensemble of convective clouds on their environment and the large-scale influence imposed back on the convective-scale dynamics. Efforts to seek observational evidence for this problem, however, are challenged by limitations in the capability of measuring vertical motion across different horizontal scales. We have recently been exploring new analysis strategies in hopes to make this seemingly impossible possible, exploiting a suite of satellite instruments including the CloudSat and TRMM radars and Aqua AIRS. Since a complete vertical structure of in-cloud vertical velocity, wc, is unable to be reconstructed from satellite measurements alone, a single-column plume model is run with the environmental soundings from AIRS to obtain a set of synthetic wc profiles under a range of entrainment rates. The solutions are then narrowed down in a Bayesian manner so as to match the cloud-top buoyancy estimates from A-Train infrared and radar measurements (Masunaga and Luo, 2016). The vertical profile of large-scale mean vertical motion, ω, is also evaluated from satellite observations in its own approach: ω as a function of pressure is determined so that it satisfies the horizontal divergence terms in the tropospheric water and thermal budget equations in which the remaining terms are constrained by satellite measurements (Masunaga and L’Ecuyer, 2014). In this talk, the methodology is briefly outlined and the results are presented and discussed in light of outstanding issues in tropical dynamics. The wc and ω estimates above, although subject to intrinsic uncertainties yet to be verified, do not involve any closure assumption as required for cumulus parameterizations and would offer a useful test bed for climate models and reanalysis data as well as a unique opportunity to study the mechanism of tropical convection.

• Title: TBD
• Time: 13:30 - 15:00 on Oct. 18, 2016.
• 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: The Quasibiennial Oscillation (QBO) - More than Six Decades of Regular Behavior (1953-2015) Disrupted by an Exceptional Event in 2016
• Time: 13:30 - 15:00 on Sep. 12, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: Far above the equator between roughly 90 hPa and 3 hPa the prevailing wind is observed to change from strong easterlies to strong westerlies roughly every other year in a quasi-regular cycle. In the observed record since 1953, the period from cycle-to-cycle has varied between about 22 and 36 months and seems to average about 27 months. This phenomenon is known now as the familiar Quasibiennial Oscillation (QBO) and is probably the most predictable aspect of the circulation anywhere in the atmosphere (other than the astronomically-forced annual and diurnal cycles, of course). The prevailing zonal-mean zonal winds in the tropical stratosphere can be quite skillfully forecast for at least several months in advance. We believe that the stratospheric QBO systematically affects the tropospheric circulation and so the QBO potentially provides some useful contribution to seasonal weather forecasting. The predictability that has been found is a reflection of the regular and nearly-repeatable evolution of the stratospheric QBO. In this talk I will identify the key aspects of QBO behavior in the observational record and briefly describe the wave-mean flow theory that we think provides the basic explanation for the existence of this oscillation. I will then show how the pre-2016 behavior can be characterized and analyzed by application of non-linear principal component analysis (NLPCA). The NLPCA approach enables an elegant and compact description of the observed QBO behavior in the tropical stratosphere and also can serve as the basis for statistical forecasts of QBO evolution. In early 2016 expectations based on the last six decades were overturned and the regular QBO behavior was severely disrupted. Notably very thin easterly and westerly jet layers have formed near 40 hPa and 20 hPa respectively. These jets display some unprecedented upward phase propagation, and strong zonal wind accelerations have occurred at altitudes where there has been little vertical wind shear. This development has not yet been fully explained and state-of-art dynamical seasonal weather forecast systems did not predict it. As of June 2016 the winds in the tropical stratosphere remain very unusual and how this incident will ultimately be resolved is also not known. I will provide an up-to-date assessment of this mysterious phenomenon. I will also show that somewhat analogous QBO disruptions are seen very occasionally in some long-running climate simulations. There is a suggestion in the model results that such events may be seen more frequently as global climate warms in response to increased greenhouse gas concentrations.

• Title: Next-generation GFDL climate model CM4
• Time: 13:30 - 15:00 on Aug. 25, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: In preparation for the IPCC 6th assessment, many of us at GFDL have been engaged in the development of a new climate model (CM4) for the last 4 years. In this talk, I will review the model formulation, key features of atmospheric physics parameterizations, quality of the simulated mean climate and variability. Toward the end, I will share some thoughts about future development as model resolutions approach the so-called "grey zone."

• Title: Modulation of stratocumulus to cumulus transition by rain
• Time: 13:30 - 15:00 on Aug. 22, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: The stratocumulus to cumulus transition (SCT) is associated with a warming sea surface temperature westward of cold ocean waters, formation of boundary layer decoupling, appearance of penetrative cumulus, and then gradual dissipation of the stratocumulus. The typical time scale for the SCT is about three days, and the system enters the cumulus regime sometime thereafter. In addition, the time scale of the transition is thought to be largely determined by the lower tropospheric stability in the stratocumulus state. In this study, the modification of the rate of the SCT due to rain is investigated with three-day Lagrangian large eddy simulations. Our model includes a two-moment bin-emulating microphysics scheme coupled with prognostic aerosol number concentration. Range of initial aerosol loading between 100 cm-3 and 250 cm-3 is tested. In our simulations, drizzle eventually forms and triggers an early transition. Local penetrative cumulus in the relatively weak decoupling region eventually reaches more significant depth, transporting surface moisture into the clouds and creating locally strong rainfall. Once rain precipitates, its couples whole boundary layer, which leads to rapid stratocumulus breakup due to density currents (divergence-convergence) associated with rain. For this scenario, SCT is considerably accelerated by rain. Thus modulation of the rate of the SCT time due to rain is significant.

• Title: Response of Tropical Cyclone Tracks to Sea Surface Temperature in the Western North Pacific (西部北太平洋における海面水温に対する熱帯低気圧経路の応答)
• Time: 16:30 - 17:30 on Aug. 10, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: A set of short-term experiments using a regional atmospheric model (RAM) were carried out to investigate the response of tropical cyclone (TC) tracks to sea surface temperature (SST) in the western North Pacific. For 10 selected TC cases occurring during 2002-07, a warm and a cold run are performed with 2 and -2K added to the SSTs uniformly over the model domain, respectively. The cases can be classified into three groups in terms of recurvature: recurved tracks in the warm and cold runs, a recurved track in the warm run and a nonrecurved track in the cold run, and nonrecurved tracks in both runs. Commonly the warm run produced northward movement of the TC faster than the cold run. The rapid northward migration can be mainly explained by the result that cyclonic circulation to the west of the TC is found in the steering flow in the warm run and it is not in the cold run. The beta effect is also activated under the warm SST environment. For the typical TC cases, a linear baroclinic model experiment is performed to examine how the cyclonic circulation is intensified in the warm run. The stationary linear response to diabatic heating obtained from the RAM experiment reveals that the intensified TC by the warm SST excites the cyclonic circulation in the lower troposphere to the west of the forcing position. The vorticity and thermodynamic equation analysis shows the detailed mechanism. The time scale of the linear response and the teleconnection are also discussed.
  Reference: Katsube, K., and M. Inatsu, 2016: Response of tropical cyclone tracks to sea surface temperature in the western North Pacific. J. Climate, 29, 1955-1975.

• Title: Satellite view of quasi-equilibrium states in tropical convection and precipitation microphysics
• Time: 13:30 - 15:00 on Aug. 8, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: This study shows the time series of statistical composites of precipitation-microphysics signals derived from long-term Tropical Rainfall Measuring Mission (TRMM) satellite observations aggregated over the entire tropical domain (37N-37S). The result shows the nearly time-invariant monthly signal statistics throughout this time, confirming convection quasi-equilibrium (CQE) states. Merged precipitation data, with much better temporal and spatial coverage, provide evidence that the equilibrium state occurs on a daily scale. These results further indicate the presence of precipitation microphysics quasi-equilibrium (MQE) within the CQE environment. A simple analytic microphysics framework illustrates the equilibrium precipitation size distribution, as compared with the TRMM radar-based as well as preliminary Global Precipitation Measurement combined retrievals. The MQE readily explains the near-constant tropical precipitation rate, which is roughly balanced with atmospheric radiative cooling rate at the entire tropical scale. Further investigation is required through theoretical, observational, and numerical manners to support the MQE hypothesis.

• Title: A model for super El Ninos
• Time: 15:30 - 17:00 on July 28, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: In this talk, we aim to shed some light on two aspects of the El Nino Southern Oscillation (ENSO) phenomenon that have attracted widespread attention in recent times. These are the diversity in the spatial structure of ENSO events and the existence of super El Nino events. We have revisited the problem of how the tropical atmosphere responds to deep convective heating patterns of relevance to ENSO, using a dry atmospheric model that incorporates a realistic background state. We show that atmospheric state changes brought about by El Nino constrain thermally forced solutions in such a way that SST variability is suppressed (enhanced) over the eastern (central) Pacific. This implies that coupled dynamics inherent to the Pacific cannot account for the so-called canonical ENSO pattern, which is characterized by strongest SST anomalies in the eastern Pacific. Next, we consider the importance of the downstream tropical circulation forced by Indian Ocean Dipole (IOD) events on surface winds over the Pacific. We show that the downstream circulation forced by an IOD event is strong enough to have a notable impact on SST variations over the Pacific, and consequently in perturbing the evolution of El Nino. Further, the impact of IOD events are amplified (diminished) when it co-occurs with an El Nino (La Nina) event. Our results suggest that a synchrony of IOD and ENSO dynamics is necessary for the so-called super El Nino events to develop. Finally, we argue that a large part of ENSO diversity, often presented as the existence of two kind of El Nino events, is an artefact, arising from the lumping of the rare but extreme super El Nino events together with more moderate events.

• Title: Pacific Subtropical Cells, Recharge-Discharge Oscillator, and Reversed Equatorial Zonal Transport in ENSO Phase Transition
• Time: 13:30 - 15:00 on July 28, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: Atmosphere and Ocean reanalysis data are used to study the variability of Pacific Subtropical Cells (STCs) and its causal relation with tropical climate variability. Result shows that the interior STCs transport into the equatorial basin through 9°S and 9°N is well connected with equatorial Sea surface temperature (SST) (9°S-9°N, 180°-90°W). The highest correlation at interannual timescales is contributed by the western interior STCs transport within 160°E and 130°W. Both composite analysis for El Nio and La Nia developing events and the correlation analysis of interior STCs transport convergence, equatorial warm water volume (WWV), wind stress curl and SST are performed to clarify subsurface transport processes and their time scales associated with the five stages of ENSO recharge-discharge cycle. The above result reveals an insufficiency of theoretical models like the recharge-discharge oscillator to explain the rapid phase transition of ENSO events at the peak phase. Our study indicates that anomalous equatorial zonal transport above the thermocline plays an important role in the rapid ENSO phase transition. During developing phase of ENSO, opposite zonal transport anomalies form in the western-central and central-eastern equatorial Pacific, respectively. Both are driven by the equatorial thermocline anomalies in response to zonal wind anomalies over the western-central equatorial ocean. At this stage, the anomalous zonal transport in the east enhances ENSO growth through zonal SST advection. In the mature phase of ENSO, off-equatorial thermocline depth anomalies become more dominant in the eastern Pacific due to the reflection equatorial signals at the eastern boundary. As a result, the meridional concavity of the thermocline anomalies is reversed in the east. This change reverses zonal transport rapidly in the central-to-eastern equatorial Pacific, joined with the existing reversed zonal transport anomalies further to the west and forms a basin-wide transport reversal throughout the equatorial Pacific. This basinwide transport reversal weakens the ENSO SST anomalies by reversed advection. More importantly, the reversed zonal transport reduces the existing zonal tilting of equatorial thermocline and weakens its feedback to wind anomalies effectively. This basin-wide reversal is built-in at the peak phase of ENSO as an oceanic control on the evolution of both El Nio and La Nia events. The reversed zonal transport anomaly after the mature phase weakens El Nio in the eastern Pacific more efficient than that does in the La Nina.

• Title:
  Effect of Large-scale Vertical Motions on SST-Cloud Relationship Observed Over the Tropical Oceans (Chian-Yi Liu)
  Diurnal variation of cloud and precipitation over the South China Sea during the summer monsoon onset (Wei-Ting Chen)
  The environment of aggregated deep convection (Chien-Ming)
  
• Time: 13:30 - 15:00 on July 21, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract:
  ・Dr. Chien-Ming Wu
  In this study, the environment of aggregated deep convection is investigated using a vector vorticity equation cloud-resolving model (VVM). Idealized experiments are performed under various environmental moisture with or without imposed vertical wind shear. Convective aggregation is then evaluated through diagnosing the 3-D size of an individual cloud from the model output using a six-connected segmentation method.The aggregated convection is recognized by a distinct mode with larger size in the cloud size distribution. The results suggest that aggregated convection tends to develop when column relative humidity (CRH) is larger than 80% (67%) in non-shear (shear) cases. In addition, the degree of aggregation further increases with the increase of CRH. Analyses of precipitation distribution suggest that that the probability of extreme precipitation increases with the increase of aggregated convection. The favorable environment of aggregated convection can be used to improve convective parameterizations in large-scale models.
  ・Dr. Wei-Ting Chen
  　The abrupt onset of the South China Sea (SCS) summer monsoon is a key precursor of the East Asia summer monsoon. The present study provides a climatological analysis on the evolution of diurnal precipitation and cloud vertical structures over SCS during the critical transition periods of onset. Pre-onset and post-onset composites are created from the 17-year precipitation estimates of the Tropical Rainfall Measuring Mission (TRMM) 3B42 datasets and the 4-year vertical cloud mask data based on the near‐coincident CloudSat radar and CALIPSO lidar profiles. Clear signals in the diurnal peak time and amplitude of precipitation, as well as the daytime and nighttime contrast of cloud types, cloud size, and cloud radiative forcing are observed. After monsoon onset, the northern part of SCS experiences significant intensification in diurnal cycle, with increasing frequency of deep convection cloud, anvil, high cirrus, and the growth in convective cloud size; however, the precipitation rate contributed by individual convective cloud only increases at daytime while decreases at nighttime. In the southern SCS, diurnal variation of precipitation is strong in both pre- and post-onset periods; after onset, a slight shift in diurnal phase, decreasing occurrence of extreme large type of convective clouds, and lower nighttime precipitation rate per convective cloud is observed. The current results highlight the sensitivity of moist convection processes to environmental conditions over the monsoonal regions, such as the triggering and aggregation of convection.
  ・Dr. Chian-Yi Liu
  The relationship between cloud and its environment factor had been studied for several decades. Due to the nature of cloud and conventional observations, studies may be limited in the discussion of cases. Since the meteorological satellite satellites could provide both passive and active observations, this gives us an opportunity to discover the more detail of clouds. In this talk, we will present some preliminary results for the relationships among the cloud, large-scale vertical motions and sea surface temperatures. Particular interests are focused on the regions of tropical India Ocean (TIO) and tropical Pacific Ocean (TPO). The CloudSat/CALIOPSO data sets are analyzed in conjunction with ECMWF Interim reanalysis fields. We found that the vertical motions are relative important in TIO, while TPO has additional consideration than vertical motions such as SST in summer months. The related precipitation intensity are exanimated that reveals some discrepancy between TRMM and CPR/CloudSat, which may need further verification.

• Title: Assimilation of all-sky infrared radiance from geostationary satellites for Tropical Cyclones
• Time: 13:30 - 15:00 on July 15, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: Potential impacts of assimilating satellite infrared brightness temperatures have been assessed through a series of convection-permitting observing system simulation experiments (OSSEs) and real-observation from GOES-13 assimilation experiments for Hurricane Karl (2010). We investigated the potential impacts of assimilating data from the Advanced Himawari Imager (AHI) on the Himawari-8 Japanese Geostationary Meteorological Satellite (Himawari-8) which launched in October 2014 and the Advanced Baseline Imager (ABI) on the Geostationary Operational Environmental Satellite (GOES-R) which will be launched in 2016. Our focus on the observations from these two satellites was a result both of their hemispherical coverage, including the tropical oceans where there is generally a dearth of observations but where tropical cyclone genesis and development occur, and of their high temporal and spatial resolution data. Direct assimilation of satellite infrared brightness temperatures, especially from cloudy regions, has been challenging given their strong nonlinear relationships to the underlying model fields. The nonlinearity causes huge representative error of observations, and strongly contaminates the impacts of assimilation. In this study, a flow-dependent adaptive observation error inflation (AOEI) method is proposed for assimilation of all-sky satellite brightness temperatures with an ensemble Kalman filter. This adaptive method is designed to limit erroneous analysis increments where there is large representativeness error, as is often the case for cloudy/rainy radiance satellite observations. The promising performance of this newly proposed AOEI method is demonstrated through both observation system simulation experiments assimilating all-sky brightness temperatures from future GOES-R and real-data experiments assimilating observations from GOES-13.

• Title: The MJO as a dispersive, convectively-coupled moisture wave
• Time: 13:30 - 15:00 on July 13, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: A linear wave theory for the Madden-Julian oscillation (MJO), previously developed by Sobel and Maloney, is extended upon in this study. In this treatment, column moisture is the only prognostic variable and the horizontal wind is diagnosed as the forced Kelvin and Rossby wave responses to an equatorial heat source/ sink. Unlike the original framework, the meridional and vertical structure of the basic equations is treated explicitly, and values of several key model parameters are adjusted, based on observations. A dispersion relation is derived that adequately describes the MJO’s signal in the wavenumber-frequency spectrum and defines the MJO as a dispersive equatorial moist wave with a westward group velocity. On the basis of linear regression analysis of satellite and reanalysis data, it is estimated that the MJO’s group velocity is 40% as large as its phase speed. This dispersion is the result of the anomalous winds in the wave modulating the mean distribution of moisture such that the moisture anomaly propagates eastward while wave energy propagates westward. The moist wave grows through feedbacks involving moisture, clouds, and radiation and is damped by the advection of moisture associated with the Rossby wave. Additionally, a zonal wavenumber dependence is found in cloud-radiation feedbacks that cause growth to be strongest at planetary scales. These results suggest that this wavenumber dependence arises from the nonlocal nature of cloud-radiation feedbacks; that is, anomalous convection spreads upper-level clouds and reduces radiative cooling over an extensive area surrounding the anomalous precipitation.

• Title: A study on radiative transfer effects of 3D cloudy atmosphere using a Monte Carlo numerical simulation (モンテカルロ数値シミュレーションを用いた３次元雲場の放射伝達効果に関する研究)
• Time: 13:30-15:00 on Apr. 26, 2016.
• Place: General Research Bldg. 2F room 270.
• Abstract: 雲の放射強制力は地球のエネルギー収支に大きく影響するが、その定量的評価には不確定性が大きく、気候モデル（GCM）による気候変化の予測にばらつきをもたらす主要因のひとつになっている。その中でも、空間的に不均質な雲による放射強制力の評価については、GCMで採用されている平行平板近似(PPA)による誤差は太陽放射で100%以上、地球放射では20%におよぶことが報告されている。近年では、高分解能雲微物理モデルを用いてこのような３次元雲場の放射特性を見積もる研究や、３次元雲場における放射量を簡易的に近似する方法を提案してGCMに適用する研究がある。しかしながら、これらの先行研究は理想化されたモデル雲にもとづくものが多く、実観測データにもとづいて現実の３次元雲場による短波・長波の広帯域放射フラックスを定量的に評価した研究は非常に少ない。 本研究では、実観測された３次元雲場の放射影響を定量化するために、モンテカルロ法にもとづく３次元放射伝達コードを自身で開発するとともに、NASA/A-Train衛星群に含まれるCloudSat衛星とAqua衛星の雲プロダクトから３次元雲場を観測的に構築する新しいアルゴリズムを考案した。この方法では、CloudSat衛星軌道に沿って同期して存在する雲レーダー(CPR)の鉛直分布とAqua/MODISイメジャーの雲物理量を組み合わせたライブラリを作成し、それを参照することによってMODIS観測域内部の任意の地点における雲の鉛直分布を構築する。こうして得られる実観測雲場にもとづいて、開発した３次元放射伝達コードによるシミュレーションを行い、Aqua/CERESの観測フラックス値との比較によって検証した。さらに、これまで提案されてきた種々の平行平板近似法で得られる放射フラックスを３次元放射計算から得られるものと比較し、各近似法の誤差を定量化した。

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