A Simulation of the Tropospheric General Circulation with the MRI Atmospheric General Circulation Model

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Abstract
A performance study of the tropospheric general circulation with the MRI (Meteorological Research Institute)•CM is presented for January. The MRI•CM is basically identical to the UCLA•GCM (Arakawa and Mintz, 1974; Arakawa and Lamb, 1977) with minor changes to both the dynamical and physical processes of the model. The resolution of the model is 5° and 4° in longitudinal and latitudinal directions, respectively. The top of the model is located at 100mb and the atmosphere is divided into 5 layers. Both the sea surface temperature and the sea ice distributions are specified based on the climatological data, while other variables are determined within the model either prognostically or diagnostically.The model has succeeded in reproducing basic characteristic features of the general circulation. Simulations are especially good in the tropics except that the mixing ratio of water vapor near the surface is underestimated in the model. Overall characteristics of the southern hemisphere are also simulated well. On the other hand some systematic disagree-ments between the model and the climatology are found in the vicinity of the Tibetan Plateau*. Northerly is too strong near the surface along the eastern coast of China, and easterly is also too strong in the southern periphery of the Plateau. This anticyclonic flow is cold and dry, and thus enhances evaporation in the Bay of Bengal and precipitation over the equatorial Indian Ocean. It is suggested that the effects of small scale mountain ranges should not be underscored because they determine low level flows and thus the heating distribution through the air mass transformation process over the warm ocean.Another notable defect is the poor simulation of the Aleutian low both in its position and intensity. This is consistent with the too low static stability in high latitudes due to the excessively cold temperature in the upper part of the model in high latitudes. The maximum decrease in the static stability is found in the area from Alaska to the north-western part of Canada, in agreement with the extensions of low pressure area in that direction.Arakawa and Schubert's (1974) theory is adopted in parameterizing penetrative cumulus convection. Thermal and dynamical roles of the parameterization are studied through budget analyses of heat and zonal momentum in low latitudes.