A simulation of the tropospheric general circulation with the MRI atmospheric general circulation model. Part II The July performance.

Abstract

The performance of the July simulation conducted with a five-level atmospheric general circulation model of the Meteorological Research Institute (MRI·GCM-I) is described. The model is the same as was described in Tokioka et al. (1985). The model simulates with reasonable accuracy most of the observed features of the large-scale distributions of sea-level pressure, circulation, divergent wind system and precipitation, although there are some systematic differences in relatively high latitudes in the Northern Hemisphere. Both evaporation and precipitation over the northern Eurasian Continent and Canada are excessive over the observed ones, and a false low pressure belt is found around 70°N. The followings are consistent with this deficiency: wet ground condition, persisting moisture flow from adjacent oceans, preferred condition to generate shallow cumulus convection and less stable stratification than the observed one. In the Southern Hemisphere the model successfully simulates subtropical highs, the circumantarctic low-pressure zone in sea-level pressure and the double-jet structure in the mid-tropospheric westerly wind. The velocity potential and the resultant divergent wind fields clearly demonstrate two major circulation systems in the tropics — the east-west circulation between the western Pacific Ocean and the eastern Pacific Ocean, and the northeast-southwest oriented circulation over the Indian Ocean. Characteristic features of the model-generated diabatic heating field are also discussed.