過去のCCSRセミナー (2007年度)

In this study, we used the aerosol transport model SPRINTARS [Takemura et al., 2000, 2002, 2005]. This model is coupled with CCSR/NIES/FRCGC Atmospheric General Circulation model and considers carbonaceous, sulfate, mineral dust and sea salt aerosols from various emission sources. Aerosol particles can influence the radiation budget, not only directly by scattering and absorbing radiation but also indirectly by changing the properties of cloud.

Observed data and model simulations show that the anthropogenic aerosol increase caused a solar radiation decrease in the industrial regions of Asia where economic is rapidly developing. Furthermore we analyzed details of change in the dynamical cycle in this region using model simulation and found that the surface temperature change caused by aerosol affected clouds and precipitation. The aerosol impact is as important as greenhouse gases impact. So, we should consider both effects when estimating the anthropogenic impact on climate.

In addition to this basic process, the SST may also be strongly modulated at the diurnal time scale because of the absorption of solar radiation by the upper ocean levels under light surface wind conditions. These diurnal warm-layers may form during the convectively suppressed phase of an intraseasonal event and increase even the diurnal average surface temperature. This is because the nighttimes SST is close to the mixed layer temperature while the noon SST can be increased by up to 5K. This higher SST will modify the air-sea exchanges and the boundary layer instability. These warm-layers disappear as soon as the wind increases in association with a large-scale convective perturbation. Warm-layers organised at large-scale thus increase the amplitude of the intraseasonal SST modulation and may even trigger ISV events. To address the role of warm-layers in ISV, a daily dataset of SST diurnal amplitude in the tropics is produced using COARE 3 (Fairall et al, 1996) algorithm forced by ERA-40 reanalysis. The results are validated using the global SVP drifter dataset and empiric relations from earlier studies. An important result is that warm layers tend to develop in region where the ISV is strong, confirming their potential role in the ISV amplitude. For moderate to strong warm layers (diurnal amplitude > 1K), the horizontal extension is between 1000 and 4000 km during periods of several days in agreement with the typical size of ISV perturbations. These results finally validate the use of the COARE 3 algorithm forced with surface fluxes at a horizontal scale typical of atmospheric general circulation model. In addition, this method gives an estimate of the warm layer depth and temperature at each physical time scale, making it usable as a parameterization. The implementation of this warm layer parameterization in the LMD GCM is further tested and its impact on the representation of the ISV in the model will be presented.

Fairall C. W., E. F. Bradley, J. S. Godfrey, G. A. Wick, J. B. Edson, and G. S. Young, 1996: Cool-skin and warm-layer effects on sea surface temperature. J. Geophys. Res, 101, 1295?1308.

Maloney, E. D., and A. H. Sobel, 2004: Surface fluxes and ocean coupling in the tropical intraseasonal oscillation, J. Clim., 17, 4368-4386. Sobel, A. H., and H. Gildor, 2003: A simple time-dependent model of SST hot spots. J. Clim., 16, 3978-3992.

実際，数値モデルで再現される深層海洋大循環のパターンや強さは，中・深 層における小規模スケールの乱流拡散過程に大きくコントロールされている． Munk and Wunsch (1998) によれば，平均的な密度成層を維持するためには 1000 m 以深でオーダー 10^{-4} m^{2} s^{-1} の乱流拡散が必要となる．乱 流拡散過程に必要なエネルギーは大気擾乱や，海底地形と潮汐との相互作用に よって生じる内部潮汐から供給されると考えられるが，このオーダーの乱流拡 散をまかなうためには全球で約 2.1 TW (1 TW=10^{12} W}) のエネルギーフラッ クスが必要となる．

このうち内部潮汐から供給されるエネルギーフラックスは，天体観測によるエネ ルギー散逸率の計算などから 0.9 TW 程度と見積もられているが，大気擾乱か ら与えられるエネルギーの直接の見積もりは十分になされておらず，潮汐と大 気擾乱とのどちらが乱流エネルギーの主要な供給源なのか未だに明らかにされて いない．

本研究では今まで未解明のまま残されていた「大気擾乱から海洋へ供給されるエ ネルギーフラックスを定量的に見積もる」とともに，「大気擾乱によって励起さ れた内部波が形成する乱流ホットスポットの時空間分布」に関する考察を行う．

Inoue (1985) found the differential absorption by ice for the split window. He developed a method to classify cloud type objectively including cirrus cloud which had been hard to classify objectively from single infrared data. Further, total precipitable water (TPW) can be retrieved from the split window over cloud free ocean area. Thus, we can retrieve SST and TPW over the clear ocean area and can retrieve cloud parameters over cloudy area, with the use of the split window. Using this split window, some results on cloud type classification, lifecycle of deep convection, monsoon etc will be introduced in my talk.

[Topics]

・Situation Analysis

・Petascale Ambitions: National/Regional Projects; CCSM Petascale Experiment

・Cray Corporate Update

・Cray Product Update

・Cray Earth Sciences Segment Update: General Overview; Porting to an MPP System; Application Performance;

[Profile]

Per Nyberg is the Marketing and Business Development Director for the Earth Sciences Segment at Cray Inc. Since joining the company in 2002, Mr. Nyberg has been responsible for Cray's worldwide strategic planning, business development and marketing for the earth sciences segment working extensively with many weather and climate centers worldwide. Prior to joining Cray, he worked for 12 years in NEC Corp's high performance computing business in Canada, United States and Australia, in roles ranging from software engineering to business development.

1. Can the lidar separate photo-multiplier-detector-delayed surface returns from the true ocean sub-surface returns?

2. How deep can we profile the ocean sub-surface backscatter?

3. How well are the CALIPSO sub-surface return correlated with Aqua/MODIS ocean color?

4. Can we derive ocean surface wind from the lidar surface return?

5. Any chance of figuring out ocean mixed-layer depth?

6. Can we use CALIPSO for Bathymetry studies?

This talk will summarize our recent studies regarding these topics, as well as initial results on ocean-ecosystem, aerosol and climate feedbacks.

Some of interesting findings are as follow:

* The diurnal variation of UTH tends to reach a maximum during nighttime over land, lagging deep convection and high cloud whose maxima occurred in the late afternoon and evening, respectively.

* Diurnal variations over the African continent are likely associated with continental-scale daytime solar heating and topography.

* Topographically-induced signals develop earlier around the mid-afternoon and merge into stronger and broader continental-scale convection clusters later, forming a precipitation maximum in the late afternoon.

* Advection effect on the diurnal variation appears to be insignificant.

In addition I like to discuss physical properties of the "warm water vapor" pixels shown in the geostationary satellite, and their possible use for a better understanding of the atmospheric phenomena in the TTL altitudes.

大気と海洋の流れは太陽からのエネルギーによって動く大変効率の悪い（０． ８％程度）熱エンジンである。熱帯と極地で太陽から直接受ける放射エネルギー に差がありそのために温度差を生じる。大気と海洋の流れはこの温度差を減少 させるようにエネルギーを熱帯から極地へ移動させる。海洋のエネルギー蓄積 は無視できるという仮定の下で、緯度方向の大気と海洋の単位時間あたりのエ ネルギー輸送はサテライトにより全球規模での大気上端放射収支を観測するこ とで見積もることができる。したがって、放射収支は気候モデルを開発するに あたって大変重要である。このため長期的な全球規模でのサテライトからの放 射収支の観測は温暖化をモデルするあったっては不可欠である。

この重要な放射収支のデータを供給しているのがCERESである。NASA のEOS、 　Terra とAquaに搭載されたCERES　instruments　は短波と短波＋長波領域の radianceを２０００年３月から測定している。大気上端放射フラックスは angular distribution models により測定されたradianceから見積もることが できる。その過程で、Moderate Resolution Imaging Spectroradiometer (MODIS) のデータより抽出された雲およびエーロゾルの物理特性と組み合わせ て大気上端放射フラックスの誤差を少なくしている。セミナーではこのプロセ スを簡単に説明する。

このCERES の２０００年３月から２００４年２月までの観測により見積もられ た大気上端放射フラックスを使い、この期間の北極地の大気上端アルベドの変 化の解析を行った。この期間は夏時の sea ice 及びsnow　の総量が急激に減 少しているとの研究結果が報告されている。MODISにより見積もられた夏時の 雲の総量は北極地全域の８０％に達しそれにより地表面のsea ice とsnow の 総量の変化による大気上端アルベドの変化は緩和される。その上、解析した４ 年間の間に雲の総量が増えておりこれにより大気上端アルベドへの影響はさら に緩和されていると考えられる。そのため大気上端アルベドは解析した４年間 はほとんど変化が見られなかった。セミナーではこの結果についても説明する。

CERESでは放射モデルとMODISによって抽出された雲やエーロゾル物理特性をも とに地表面の放射収支の見積もりも行っている。セミナーではこの地表面の放 射見積もりのプロセス及びと地表面で測定された放射フラックスとの比較など を紹介する。さらにこれらの大気上端および下端の放射収支を使って全球大気 の放射収支および大気に及ぼす雲の放射効果などを見積もることができる。セ ミナーではこの全球大気の放射収支を紹介する。

The first part gives an introduction of the research in meteorology and climate we are conducting at City University of Hong Kong that may be of interest to CCSR.

The second part is some recent work examining the question of whether global warming will lead to more intense typhoons. The frequency of intense typhoon (Category 4 and 5 in the Saffir-Simpson scale) occurrence for the period 1960-2005 in the western North Pacific (WNP) at decadal time scales is analyzed. It is found that in the southeastern part of the WNP, during periods with above-normal frequency of intense typhoon occurrences, the thermodynamic conditions are more conducive to the development of tropical cyclones. As these cyclones move northwestward, the favorable dynamic conditions continue to be present so that they can intensify further. The steering flow ensures many of these typhoons will stay over water for an extended period of time through low-latitude recurvature. As a result, they can intensify to become Category 4 or 5 typhoons. The conditions during the below-normal periods are generally opposite.

A major conclusion from the results of this study is that the frequency of intense typhoon occurrence does not exhibit a linear increasing trend. Rather, it undergoes a strong multi-decadal variability due to similar variations in the planetary-scale oceanographic and atmospheric conditions that govern the formation, intensification and movement of tropical cyclones.

その結果、氷期氷床上の融解は表面気温、下向き短波放射と表面アルベドに依 存し、氷期氷床の様に現在の氷河氷床に比べて広範囲に分布する場合は、特に 下向き短波放射と地表面アルベドが地域や気候条件にて変化することを考慮す る必要があることがわかった。

氷期氷床上の降雪は、氷床の地形と高アルベドによる表面気温の寒冷化と大気 循環場の変化の影響により、内陸部では現在氷床に基づく経験則よりも強い減 少率を示すこと、減少率は季節性を持つこと、加えて氷床縁辺部では降雪の増 加が起こることがわかった。減少率の地域性・季節性は最終氷期極大期の氷床 体積に影響すること、縁辺部での降雪の増加は氷床成長のフィードバックとし て働く可能性が示唆されることがわかった。

I will first give a historical review on the justification of TA which has been “rather confusing” as Norman Phillips wrote in 1966. A renewed interest in questioning the wisdom of TA has revived in the last ten years or so due to an effort to improve the fidelity of the models for weather and climate. I will then summarize recent findings on the role of Cos-Coriolis terms. Without the TA, the axis of rotation is no longer parallel with the gravity, except at the poles. This reality together with the influence of vertical boundary creates little-known inertio-gravity modes in addition to the traditional ones. In other words, with the TA the accuracy of inertio-gravity motions is compromised. Lastly, I will propose a dynamical framework of future earth system model using unified radial coordinates for the atmosphere and hydrosphere with only one minor assumption that the geopotential of the earth is a sphere.

Interactive surface fluxes are essential to the dynamics of intraseasonal variability in some idealized models, both of the eastward-propagating MJO and the northward propagating variations of the Asian monsoon. By no means do all idealized models exhibit such behavior, however. In general circulation models, it is straightforward to estimate the importance of interactive surface fluxes. Such sensitivity tests have been done in only a small number of models, with inconsistent results. The authors suggest that it would be useful to know the importance of surface fluxes to intraseasonal variability in a larger number of models. This knowledge might provide some insight into the relevance of interactive surface fluxes to intraseasonal variability in nature, thus making it possible to rule out some theoretical explanations of intraseasonal variability (either those in which surface fluxes are crucial, or those in which they are not).

I will present a couple of different pieces of work which use observations to test some aspects of our current understanding of what controls TC statistics. I will show that interannual variations in the maximum intensities reached by TCs in the north Atlantic and western north Pacific are, within the uncertainties imposed by the best track data, consistent with potential intensity theory. I will also show that a genesis potential index recently developed by Emanuel and Nolan gives a good prediction of interannual TC number variations in most basins associated with ENSO. This is a real test of the index, as it was trained only on climatology, with no knowledge of interannual variations. The index then allows the variations to be attributed to particular physical factors, e.g. there are fewer storms in the Atlantic during El Nino years because of increased vertical shear.

We will also show that above-mentioned relationship is modulated by the tropical quasi-biennial oscillation (QBO) wind in the stratosphere. In the QBO easterly phase, a significant warming appears in northeastern Asia in the presence of high wave activities. This corresponds to a weakened East Asian trough at 500-hPa, which determines the extent to which cold waves penetrate into East Asia. However, in the QBO westerly phase, both the surface warming and the weakening of the East Asian trough become insignificant in response to high wave activities. The possible mechanism for this QBO modulation on the tropospheric wave activities may be attributed to the indirect influence of the QBO induced polar and extratropical stratospheric circulation changes. Under the QBO easterly phase conditions, the tropospheric wave activity flux divergence in the higher-latitude region is enhanced due to enhanced upward EP flux into the stratosphere, while the wave flux convergence in the subtropical troposphere is increased due to the decrease in the equatorward flux. This leads to an enhanced wave activity difference and thus the associated East Asian climate anomalies become larger and robust. An opposite effect (i.e., reduced wave activity difference) appears in the QBO westerly phase. Further analyses reveal that the QBO significantly modulates both the zonal wavenumber 1 and 2 in the sea level pressure field but not for wavenumber 3. The combination of wavenumber 1 and 2 patterns leads to the strongest surface temperature anomalies in northern Asia.

The complex 3-D Eulerian model CMAQ and related components newly developed in this study are applied, for the first time, to quantify region-to-region source-receptor relationships (SRRs) for both sulfur and reactive nitrogen in East Asia. We proposed a source region attribution methodology by analyzing the non-linear responses of the Eulerian model to emission changes. The transboundary influence exhibits strong seasonal variation and is generally peak during the dry seasons, reflecting the Asian monsoon circulation. Long-range transport from central eastern China contributes a significant percentage (>20%) of anthropogenic sulfur deposition as well as reactive nitrogen deposition throughout East Asia. At the same time, northwestern China receives approximately 35% of its sulfur load and 45% of its nitrogen load from foreign emissions, mainly from the Indian subcontinent. Volcanic sources, including emissions from Miyakejima volcano in 2001, contribute approximately 50% of the total sulfur deposition in Japan. Sulfur inflows from regions outside the study domain, which is attributed by using boundary conditions derived from the MOZART global atmospheric chemistry model, are pronounced (10-40%) over most parts of Asia. Compared with previous studies using simple Lagrangian models, the results derived in this study indicate higher influence from long-range transport. The estimated source-receptor relationships are believed to be more realistic since they include global influence as well as internal interactions among different parts of China.

The second part of this seminar focuses on our recent work related to intraseasonal Kelvin waves produced by the MJO using ocean general circulation model (OGCM) experiments. Previous observational work has demonstrated that the phase speed of oceanic equatorial Kelvin waves forced by the Madden-Julian oscillation (MJO) appears to vary substantially. Processes that are responsible for systematic changes in the phase speed of these waves are examined using an OGCM. The model is able to reproduce observed systematic changes of Kelvin wave phase speed reasonably well, providing a tool for the analysis of their dynamics. The relative importance of the upper ocean background state and atmospheric forcing for phase speed changes is determined based on a series of additional model experiments with various surface forcings.

The key component of the coupled system is a newly-developed air-sea momentum flux parameterization based on the wave fields (Moon et al., 2004a-c). In the coupled system, the complete wave spectrum is constructed by merging the WW3 spectrum in the vicinity of the spectral peak with the spectral tail parameterization. The result is incorporated into the WBL model to explicitly calculate the wave induced stress, the mean wind profile, drag coefficient, and the roughness length. In the coupled system, the estimated wave-field dependent roughness length is transferred into the GFDL model, replacing z0 of the current GFDL hurricane model based on the Charnock relation. For computational efficiency, we introduce a movable grid mesh configuration for the wave model as well as the MPI parallel computing system for the coupled model.

We have tested and evaluated the new coupled system for Hurricane Isabel (2003), Ivan (2004) and Katrina (2005) by comparing the storm intensity forecasts and the spatial distributions of the surface wind with and without the wave coupling. The results shows that the wind structure with the wave coupling is evidently in a better agreement with the HRD wind analysis and its intensity forecast is significantly improved. This is accomplished by the use of more realistic wave-dependent surface momentum fluxes and their spatial distribution. For surface wave and storm surge simulations, the introduction of the new momentum fluxes from the coupled model contributes to improving forecast skill (Moon et al., 2007, 2008).

References

Moon, I.-J., T. Hara, I. Ginis (2004a), Effect of surface waves on air-sea momentum exchange. Part I: Effect of mature and growing seas, J. Atmos. Sci., 61, 2321-2333.

Moon, I.-J., I. Ginis, T. Hara (2004b), Effect of surface waves on air-sea momentum exchange. II: Behavior of drag coefficient under tropical cyclones, J. Atmos. Sci., 61, 2334-2348.

Moon, I.-J., I. Ginis, and T. Hara (2004c), Effect of surface waves on Charnock coefficient under tropical cyclones, Geophys. Res. Lett., 31, L20302..

Moon, I.-J., I. Ginis, T. Hara, B. Thomas, (2007), A Physics-based parameterization of air-sea momentum flux at high wind speeds and its impact on hurricane intensity predictions, Mon. Wea.r Rev. 135, 2869-2878.

Moon, I.-J., I. Ginis, T. Hara, B. Thomas, (2008), Impact of reduced drag coefficient on ocean wave modeling under hurricane conditions , Mon. Wea. Rev. In press.

静止衛星は広い視野を短時間間隔で観測でき，熱帯域に遍在する上層雲 を効率よく観測できる．衛星観測を用いて非降水性上層雲の物理量を推 定する手法は既に多数提案されている．これらのうち，11umと12umの等 価黒体温度（TBB）観測を用いるsplit window法は昼夜を問わず利用でき， また殆どの現行静止衛星に適用できる有用な手法である．しかしながら， 非降水性上層雲を直接観測できる測器が限られているために，観測デー タによる検証が十分とは言えなかった．

本講演では，極軌道衛星CloudSatおよびCALIPSOによる観測結果を用いた， 静止衛星split-window TBBによる幾何・光学量の推定結果を紹介する．2006 年に運用を開始したCloudSatおよびCALIPSOは，それぞれミリ波雲レーダ とライダを搭載しており，非降水性上層雲の鉛直構造を観測できる．観 測結果をsplit-window TBBで回帰することで得られた推定値の分布は， おおむね理論的な予測値と対応している．しかしながら，特にTBBが低く 光学的に厚い非降水性上層雲について，単純な理論による予測値との差 異が認められた．

(1) Physical processes in atmospheric models

This lecture introduces the fundamentals of the parameterization of physical processes in atmosphere. The basic concept of parameterization of each individual physics forcing such as radiation, surface layer and boundary layer turbulence, precipitation processes will be introduced. The existing numerical algorithms for each physical process will be introduced. An advanced physics package for numerical weather forecasts and climate prediction will be introduced.

(2) Interaction between the boundary-layer and precipitation processes in atmospheric models

This talk describes the background of the physics parameterization scheme development, focusing on the turbulence vertical diffusion and precipitation algorithms. The hierarchy of the Yonsei University (YSU) PBL (Hong et al. 2006, Mon. Wea. Rev.) for vertical diffusion, and the Weather Research Forecasting (WRF) Single-Moment bulk parameterization scheme (Hong et al. 2004, Mon. Wea. Rev) for microphysics scheme will be described, together with its further revision strategy. Not only the validation of the scheme over the theoretical study and observations, but also the interaction between the boundary-layer and other physics algorithms will be highlighted to accomplish the improvement of numerical weather forecasts and climate prediction in atmospheric models.