Newsletter No.4 October-1998　

I have joined the Global Warming Research Program and belong to the Paleoclimate Research Group.Before I came here, I worked on variability of the thermohaline circulation on the timescales ranging from a century to millennia using a two-dimensional (one horizontal and one vertical axes)thermohaline circulation model of the oceans,which may be coupled to an atmospheric EBM (energy balance model).I am still working on the same topic but started using a full three-dimensional OGCM,namely GFDL Modular Ocean Model. One such possible paleoclimate event that is closely related to this topic is the so-called Dansgaard-Oeschger oscillation that can be clearly observed in the paleoclimatic records for the late glacial in the last Ice Age cycle.The millennium timescale quasi-periodic climate change has been revealed through analyses of temperature proxy in the ice cores from Greenland,and the amplitude of the oscillation is more than half that of the glacial-interglacial temperature change itself. There has also been revealed similar variability in the North Atlantic paleoceanographic records that can be correlated to the Greenland records. I will continue investigation the climate variability focusing on the role of the North Atlantic thermohaline circulation. 對馬 洋子 Ms.Yoko Tsushima 皆さん、こんにちは。 　温暖化グループの目標に、大循環モデル(GCM)を用いて現在と氷期・温暖期・CO 2 による温暖化など異なる気候ごとにシミュレーションを行ない、現在の気候との違いを記述して変動のメカニズムを解明することがあります。 　私はその中で、気候変動において雲と放射の果たす役割に注目しています。そのために気候変動における雲の変化と、それによる放射場の変化、大規模場とのつながりを解析します。 大気上端の放射収支は気候を決める重要な要因であり、雲はその放射収支に大きく寄与する要素なのです。 　このように地球温暖化などの気候変動問題を考える場合、モデルを用いることはひとつの有効な手段ですが、変動に対するパラメーターの応答がモデルで適切に表現されているかどうかを確認することも必要です。 　特に雲水量に関してはモデル間の表現の違いが温暖化による地表面温度の変化の見積りにばらつきを与えている原因であることが指摘されています。 　そこで、観測データが入手可能な気候変動のうちシグナルの大きい季節変動に着目し、季節変動における大気場と雲水量の変動の関係の解析を進めています。 　その結果を用いてモデルを評価し、パラメタリゼーションの改良点を具体的に捉えることができると期待しています。 Hello there ! One of the purpose of our Global Warming Research Group is to describe variations of mechanisms of different climates such as present period,the last maximum and minumum period of near surface temperature(the last glacial maximum, the mid-Holocene),double CO2 period and to understand the mechanisms of climate change by simulating each climate with the General Circulation Model (GCM)and analyzing the results.Among the analysis,I take note of roles played by cloud and radiation in the climate variations. Radiation budget at the top of the atmosphere is the first factor to determine climate,and clouds are the key element which contributes largely to the budget.I analyse variations of clouds in different climate,variations of radiative fields by it,and their relation with large-scale fields.It is a good way to use GCM in analyzing the climate change,but it is also necessary to confirm if responses of parameters to it are described properly in it or not. It has been pointed out that the different parameterizations of cloud water result in a dispersion of estimates of variations in ground surface temperatures by the CO2 warming in GCMs. I proceed with analysis of the relation between the atmospheric field and the amount of cloud water in seasonal variations, which are climate variations with fairly big signals and of which observational data are obtainable. I evaluate the models by using their results,and expect to verify points to be improved in parameterization.