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: 多波長マルチピクセル法による大気エアロゾルのリモートセンシング・アルゴリズムの開発
• Time: 13:30-15:30 on Mar. 28, 2014.
• Place: General Research Bldg. 2F room 270.

• Title: Current global-warming hiatus tied to equatorial Pacific surface cooling
• Time: 13:30-15:00 on Mar. 18, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: Despite the continued increase of atmospheric greenhouse gases, the annual-mean global temperature has not risen in this century, challenging the prevailing view that anthropogenic forcing causes climate warming. Two schools of idea exist regarding what causes this hiatus in global warming: one suggests a slowdown in radiative forcing due to the stratospheric water vapor, the recent volcanic eruptions, the rapid increase of anthropogenic aerosols, and the solar minimum around 2009, while the other considers the hiatus as part of internal variability, especially a La Nino-like cooling in the tropical Pacific. We present a novel method of uncovering mechanisms for global temperature change by prescribing, in addition to radiative forcing, the observed history of sea surface temperature over the central to eastern tropical Pacific in a climate model. Our model reproduces the annual-mean global temperature remarkably well with a correlation coefficient of 0.97 for 1970-2012, a period including the current hiatus. Our simulation further captures seasonality of the hiatus, i.e. global temperature decrease in boreal winter and continued warming in boreal summer. It also detects major regional characteristics of the hiatus, including the intensified Walker circulation, weakening of Aleutian Low, the winter cooling in northwestern North America and prolonged drought in the southern US. Our results show that a La Nino-like decadal cooling, which is likely due to an internal variability, is the major cause of the current hiatus.

• Title: Linking evapotranspiration, boundary‐layer processes and atmospheric moisture using isotope tracer modeling and data
• Time: 13:30-15:00 on Feb. 10, 2014.
• Place: General Research Bldg. 2F room 270.
• Abstract: The stable isotope composition of water has been used to identify conditions andpathways under which water exchange occurs between global reservoirs. At continental locations, large‐scale synoptic weather cycles are a major control of the day‐to‐day variation in the isotopic composition of atmospheric water vapor. The sub-grid convection, atmospheric mixing and land processes (via evapotranspiration (ET) feedback) further modify the isotopic variation. This study uses high-quality spectroscopy measurements to place local constraints on the isotopic composition of near‐surface water vapor in an isotope‐incorporated land surface model (Iso-MATSIRO). A full‐year, near continuous observation of hourly oxygen‐18 and deuterium isotope ratios in atmospheric water vapor at Wind River field station, WA, USA, reveals times of strong influence from surface ET versus times when convective mixingdominates. These surface isotope measurements provide a robust foundation to improve the representation of the kinetic isotopic effects arising from ET and source water partitioning. Nudged, isotope‐enabled GCM (IsoGSM) simulations reproduce isotopic variations influenced by large‐scale, synoptic weather cycles, but are less successful in capturing variations associated with sub‐grid processes. Specifically, the model is unable to produce the large and consistent variability in the deuterium excess (dx) values of near-surface water vapor. This ‘terrestrial feedback’ to the atmosphere is poorly parameterized in the IsoGSM. Future effort requires improved land surface parameterization to accurately describe the kinetic (evaporative) effect, which in turn, providing powerful constraints to assess processes that control atmospheric moisture variability in climate models.

• 場所: 総合研究棟　4センター共用2階会議室 270

• Title: Aerosol-Cloud-Precipitation Interactions in View of Satellite Measurements, Process Modeling, and their Fusion
• Time: 15:00-17:00 on Dec. 17, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: Aerosols can serve as cloud condensation nuclei and ice nuclei in different thermodynamic conditions, and therefore cloud-precipitation process can be often affected by variability of the natural and anthropogenic aerosols. This seminar will provide a discussion in the aerosol-cloud-precipitation interactions through reviewing my past and current works. Topics ranges from aerosol-marine low clouds interaction to aerosol-deep convective clouds interaction by reviewing the TRMM-based observational studies and numerical modeling studies, and also discuss the issues in these approaches. This review concludes that the precipitation microphysics is a key process to understand a complex mechanism in cloud-precipitation interactions.
  For better understanding of these microphysics parameters, multi-instrument satellite simulators have been developed, and integrated mesoscale modeling and satellite direct signals. Examples shows the evaluating bulk and bin microphysics of the Goddard Cumulus Ensemble (GCE) model, and improvement of the Goddard bulk microphysics performance for past several years as demonstrated from the NASA Multi-Modeling Framework (MMF) simulations. Finally, I will discuss applications of upcoming GPM Core satellite measurements through the synthetic GPM simulator database.
  Bio. Dr. Matsui focuses on weather and climate science linking to cloud-precipitation processes, aerosol-cloud interactions, and land-atmosphere interactions by development and application of mesoscale meteorological models, satellite remote sensing, and satellite simulators. His multi-sensor satellite simulator, the Goddard Satellite Data Simulator Unit, plays a critical role to bridge high-resolution atmospheric models and various satellite missions. Currently, he is a sub-leader of the mesoscale dynamic and modeling group, and deputy Co-PI of the NASA-Unified WRF project. He has been a head committee of the GSFC AeroCenter in 2011~2013. He has been organized AGU session since 2007.

• Title: On the relation among SST, deep convection and surface winds in the equatorial Atlantic
• Time: 16:00-17:30 on Nov. 15, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: Surface winds are a key factor controlling the annual cycle and interannual variability of the equatorial Atlantic Ocean. In the present study we examine the factors controlling equatorial Atlantic surface winds in boreal spring. Both satellite observations and GCM output indicate that the equatorial zonal winds are very sensitive to the position of the Atlantic ITCZ. Analysis of interannual variability indicates that the equatorial easterlies weaken approximately linearly with ITCZ latitude for the range 8ºN to 2ºS. Thus the easterlies are weakest when the ITCZ is located south of the equator. The position of the ITCZ, on the other hand, appears not to be a simple function of the underlying SST distribution. Rather, analysis suggests that remote influences from the surrounding continents may play an important in determining Atlantic ITCZ position and thus equatorial surface winds. The implications for coupled air-sea feedbacks in the tropical Atlantic will be discussed.

• 場所: 総合研究棟　4センター共用2階会議室 270

• Title: A study of mesoscale cloud structures in the tropical region using a convection-permitting cloud model and satellite data
• Time: 14:00-15:30 on Oct. 1, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: The horizontal and vertical cloud structures are important for the precipitation and energy budget of atmosphere. The cloud microphysics of deep convective systems over the tropical open ocean simulated by a convection-permitting cloud model using satellite simulators are evaluated in terms of the joint histogram of cloud-top temperature and precipitation echo-top heights. The control experiment shows biases related to underestimation of stratiform precipitation and a higher frequency of precipitating deep clouds whose top height is higher than 12 km compared with the Tropical Rainfall Measuring Mission (TRMM) data, although it shows good agreement for the horizontal distribution and statistical cloud size distributions of deep convective systems. The biases in the joint histogram are improved by changing the cloud microphysics parameters in the framework of a single-moment bulk microphysics scheme. In particular, the effects of the size distribution of precipitating hydrometeors are examined. Global simulations are analyzed and examined using a control run and modified microphysics about characteristics of vertical cloud structures among different regions. Finally, characteristics of effective radius in the precipitation and anvil clouds are investigated using satellite data.

• Title:The activity of synoptic tropical wave and its relationship with TC genesis over western North Pacific
• Time: 13:30-15:00 on Sep. 20, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: The synoptic waves in the equatorial region mainly consist of Mixed-Rossby gravity (MRG) wave and tropical depression (TD)-type disturbance. Two kinds of tropical waves are not independent completely but can experience transition from MRG wave to TD-type disturbance. Interannual variation in wave transition is related to monsoon circulation change in response to tropical convective heating during the different ENSO phase. The northeast-southwest oriented axis of TD-type disturbances in collaboration with the monsoonal environment is, to some extent, associated with tropical cyclogenesis. A multilevel baroclinic model was used to examine the role of dynamic and thermodynamic mean state in the wave transition. Sensitivity experiments show that the dynamic effect alone cannot capture well the observed wave behaviors. Through the heating feedback with the involvement of sea surface temperature (SST) and low-level moisture, the near-surface thermodynamic fields can play a crucial role in the scale contraction and the propagation characteristics for tropical synoptic waves. In addition, the synoptic-scale equatorial response to Rossby wave energy dispersion associated with off-equatorial wave activity sources was investigated and a new mechanism for triggering low-level MRG waves was proposed. A case study reveals that a vortex related to tropical cyclogenesis generated a coherent wave train through southeastward energy dispersion, resulting in the equatorial atmospheric response consistent with the equatorially-trapped MRG wave. The study also explored the discrepancy in the equatorial responses under the different background flows corresponding to the El Niño and La Niña.

• Title:Longwave band‐by‐band flux and cloud radiative effect (CRE):derivation, validation, and application in GCM evaluation and cloud feedback studies
• Time: 15:00-16:30 on Aug. 5, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: While the TOA broadband flux and cloud radiative effect (CRE) acquired from ERBE and CERES have been extensively used in climate study and GCM evaluations, the flux and CRE over each individual absorption band (termed as band-by-band flux and CRE) has its unique strength in GCM evaluation because (1) comparing band-by-band CRE and flux avoids the compensating biases in the broadband comparison and (2) the fractional contribution of each band to the LW broadband CRE is sensitive to the cloud top height but largely insensitive to the cloud fraction, presenting a unique diagnostic metric to separate the two macroscopic properties of clouds most relevant to longwave CRE. I will first describe a series of recent studies by my group that established algorithms of deriving spectral flux from AIRS observations in a way fully consistent with CERES radiance-to-flux algorithm over the entire globe. Next I will summarize findings in our studies of using such derived spectral flux to evaluate band-by-band clear-sky fluxes and CREs simulated by three different atmospheric GCMs (GFDL AM2, NASA GEOS-5, and Canadian CCCma CanAM4). Such comparisons quantitatively demonstrate the compensating errors originated from different bands as well as different spatial patterns of biases in different bands, which can be further attributed to underlying physical processes. The merit of IR-effective cloud top height and cloud amount for GCM evaluation will be also discussed, as well the relation with other satellite- derived cloud products. If time allows, I will also present a recent study of comparing far-IR spectral flux derived in such way with those computed from three most recent reanalyses, ECMWF ERA-interim, NASA MERRA, and NCEP CFSR.
  References:
  1. Huang, X.L., J. N.S. Cole, F. He, G.L. Potter, L. Oreopoulos, D.M. Lee, M. Suarez, N.G. Loeb, Longwave band-by-band cloud radiative effect and its application in GCM evaluation, Journal of Climate, 26(2), 450-467, doi:10.1175/JCLI-D- 12-00112.1, 2013.
  2. Chen, X.H., X.L. Huang, N. G. Loeb, H. L. Wei, Comparisons of clear-sky outgoing far-IR flux inferred from satellite observations and computed from three most recent reanalysis products, Journal of Climate, 26(2), 478-494, doi:10.1175/JCLI-D-12-00212.1, 2013.
  3. Huang, X.L., N.G. Loeb, and W.Z. Yang, Spectrally resolved fluxes derived from collocated AIRS and CERES measurements and their application in model evaluation: 2. cloudy sky and band-by-band cloud radiative forcing over the tropical oceans, JGR-Atmospheres, 115, D21101, doi:10.1029/2010JD013932, 2010.
  4. Huang, X.L., W.Z. Yang, N.G. Loeb, and V. Ramaswamy, Spectrally resolved fluxes derived from collocated AIRS and CERES measurements and their application in model evaluation: 1. clear sky over the tropical oceans, Journal of Geophysical Research-Atmospheres, 113, D09110, doi:10.1029/2007JD009219, 2008.
  

• Title: PNA-like climate teleconnections in continental North America during the mid- and late Holocene epoch
• Time: 13:30-15:00 on Jul. 26, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: The Pacific North American (PNA) teleconnection pattern has a strong influence on North American climate. Instrumental records and century-scale reconstruction1 of the PNA indicate an accelerating positive trend since mid-1850s, but much less is known about long-term variability of the PNA. Here, we use two paired speleothem and lake sediment isotope records retrieved from two regions (Northwest, NW and Southeast, SE) in North America with robust, anticorrelated isotopic expression of the modern PNA to reconstruct the PNA variability during the mid- and late Holocene. We identified a mean state of more negative PNA-like climate during the mid-Holocene but a more positive one during the late Holocene. Superimposed on the secular change is a robust, quasi-200-year oscillation in PNA response to de Wries2 solar cycle. These findings provide evidence of PNA-like climate variability throughout the mid- and late Holocene and may help deconvolve paleo-PNA pattern variations from changes in other local climate variables and/or global teleconnection patterns.

• Title:Impacts of air-sea coupling and cloud/precipitation processes on tropical climate in a general circulation model
• Time: 13:30-15:00 on Jul. 19, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: In this study, the impacts of cloud/precipitation processes, partial cloudiness parameterization, cloud-radiation interaction, and air-sea coupling, on tropical climate are investigated using atmospheric general circulation model (AGCM) and atmosphere-ocean general circulation model (AOGCM) frameworks. In addition to a typical coupling of ocean-atmosphere on a daily basis, the diurnal variation of Sea surface temperature (SST) is considered by accounting for the ocean mixed layer and surface-energy budget at the skin ocean. First, the seasonal climate simulation from both the atmosphere-only model and the coupled climate model are evaluated and compared. Seconds, it is investigated the sensitivity of a simulated tropical precipitation climatology focusing on the ISO to four convective parameterization schemes: simplified Arakawa-Schubert (SAS), relaxation Arakawa-Schubert (RAS), new Kain-Fritsch (KF2), National Center for Atmospheric Research (NCAR) Climate Model version 3 (CCM), using the AOGCM. Finally, the convective parameterization scheme is revised and partial cloudiness parameterization is developed in AGCM for realistic cloud-radiation interaction and tropical climate simulation.

• Title:Use of A-Train Observations to Study Convective Dynamics: From the Core to the Outflow
• Time: 13:30-15:00 on Jun. 7, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: A-Train constellation provides a suite of synergistic passive and active observations of clouds. While the original purpose of the passive-active synergy was to improve retrievals of cloud radiative and microphysical properties, they have also spurred the development of innovative analysis methods and new concepts that go beyond just remote sensing algorithm development. The unique data collected have led to novel applications that enable us to probe the underlying cloud dynamical processes from a global perspective. This talk will use a few examples from the authors’ recent publications to illustrate how A-Train observations can be used to understand convective dynamics, including 1) convective buoyancy and entrainment rates associated with the convective core, 2) level of neutral buoyancy as inferred from convective outflow, 3) and comparison between observations with parcel theory predictions. These new analysis tools will facilitate the use of satellite observations to evaluate GCM cumulus parameterizations.

• Title:Fast and ultrafast Kelvin wave behavior simulated by the Kyushu-GCM
• Time: 13:30-15:00 on May 9, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: Eastward-propagating 6-10 days period fast and 3-6 days period ultrafast Kelvin waves in the middle and upper atmosphere play an important rule to couple the lower and upper atmosphere because of their long vertical wavelength and vertical propagating properties. Due to the limitation of the observation abilities of present measurements, the detailed wave behaviors in the middle atmosphere have not be revealed yet. The relation between wave activities and semiannual oscillations, stratosphere semiannual oscillation (SSAO) and mesosphere semiannual oscillation (MSAO), in the middle atmosphere is also left uncertain because the shortage of observational data. This study uses the middle atmosphere atmospheric general circulation model developed by Kyushu University (the Kyushu-GCM) to reveal the properties and behaviors of fast and ultrafast Kelvin waves. In this seminar, (1) the wave properties of fast and ultrafast Kelvin waves in the middle atmosphere and (2) the relation between Kelvin waves and SSAO/MSAO simulated by the Kyushu-GCM will be introduced.

• Title:Mechanisms of ocean-atmosphere interactions over the Kuroshio and the Gulf Stream
• Time: 16:00-17:30 on Apr. 25, 2013.
• Place: General Research Bldg. 2F room 270.
• Abstract: In this talk, motivated by recent observations of co-variations of sea surface temperature (SST), ocean currents and atmospheric circulation changes, I will put forward a new mechanism for the impact of meridional shifts of the Kuroshio on the North Pacific storm track. The new mechanism relies on an east-west reorganization of the heat transport due to atmospheric transient waves in response to changes in SST at the western boundary. The large sensitivity of transient eddy heat transport to SST is proposed to result from the interaction of weather fronts with the upper ocean through a combination of convective and inertial instabilities. Moist processes are key to the dynamics of these instabilities.

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