Dynamic and Thermodynamic Influences of the Tibetan Plateau on the Atmosphere in a General Circulation Model

Abstract

The dynamic and thermodynamic influences of the Tibetan Plateau on the temperature geopotential height, horizontal wind, vertical velocity, cloud and precipitation patterns over eastern Asia am physically investigated employing a general circulation model specifically designed for medium range weather prediction. The model is a modification and improvement of the one recently presented by Liou and Zheng. Efficient and accurate numerical techniques have been devised for the computation of the pressure gradient force and the initial field in the vicinity of mountains in the σcoordinate. In addition, a cumulus convection scheme and a liquid water content prediction equation from which the large-scale precipitation may be evaluated have been developed. Utilizing the NMC objective analysis data covering the period from 13 May to 18 May 1979 and in light of the general circulation model experimentation, we find that incorporation of the mountain and the subsequent diabatic heating effects improves the overall modeling results for the temperature, geopotential height and wind fields, especially in low and middle levels. Without the consideration of the mountain effect, the prediction results from the model in the low level deteriorate and errors propagate into levels aloft. The thermodynamic effects involving radiation, condensation and the vertical transport of sensible heat are found to he very important in the maintenance of the position and intensity of the eastern Asia jet stream. Moreover, the presence of the orographic barrier strengthens the vertical velocity, and the effects of the facing and lee sides of the plateau on atmospheric flows significantly influence the prediction of temperature and geopotential height fields. Finally, it is observed that the formation of cloud and precipitation distributions east and south of the plateau is a direct consequence of the coupling of dynamic and diabatic heating effects caused by the plateau.