Tatsushi Tokioka

AMIP Simulations of the MRI GCM.

This paper summarizes the results of a 10-year integration of the MRI GCMs participating in the Atmospheric Model Intercomparison Project (AMIP). Models are integrated with the lower boundary conditions of the observed SST and sea ice distributions from January 1979 to December 1988. Standard outputs with the 15-layer model are compared to observations and those with the 5-layer tropospheric model. It is shown that some of model deficiencies in the 5-layer model reported in previous papers are improved in the new 15-layer model climatology. Some of the differences in interannual variations in the mid-latitudes responding to the tropical SST forcing between the two models can be attributed to different model climatology.

Effect Of Eurasian Snow Cover On Summer Climate Of The Northern Hemisphere: A GCM Study

Observational studies have shown that Eurasian snow-cover anomalies during winter-through-spring seasons have a great effect on anomalies in atmospheric circulation and climate in the following summer season through snow albedo feedback (Hahn and Shukla, 1976; Dey and Bhanu Kumar, 1987). Morinaga and Yasunari (1987) have revealed that large-scale snow-cover extent over central Asia in late winter, which particularly has a great effect on the circulation over Eurasia in the following season, is closely related to the Eurasian pattern circulation (Wallace and Gutzler, 1981) in the beginning of winter. Some atmospheric general circulation models (GCM) have suggested that not only the albedo effect of the snow cover but also the snow-hydrological process are important in producing the atmospheric anomalies in the following seasons (Yeh and others, 1984; Barnett and others, 1988). However, more quantitative evaluations of these effects have not yet been examined. For example, it is not clear to what extent atmospheric anomalies are explained solely by snow-cover anomalies. Spatial and seasonal dependencies of these effects are supposed to be very large. Relative importance of snow cover over Tibetan Plateau should also be examined , particularly relevant to Asian summer monsoon anomalies. Moreover, these effects seem to be very sensitive to parameterizations of these physical processes (Yamazaki, 1988). This study focuses on these problems by using some versions of GCMs of the Meteorological Research Institute. The results include the evaluation of total snow-cover feed backs as part of internal dynamics of climatic change from 12-year GCM integration, and of the effect of

Parameterization of Subgridscale Mixing Based on Quasi-Geostrophic Turbulence Theory

準地衡風乱流論に基づくサブグリッドスケールの混合のパラメタ表示の一方法を提案する。このパラメタ表示では運動量及び熱に対する水平拡散の係数と同時に、それらに対する垂直拡散の係数も一義的に決定される。 拡散の係数の決定法の他に、拡散の差分表現についても検討を行なう。エンストロフィーがより小さいスケ一ルの乱れの方に流れて行く時の慣性小領域を適切に表現する拡散の差分表現法についても述べる。