ANALYSIS OF THE CIRCULATION EVOLUTION AND WATER VAPOR TRANSPORT OF A RARE TORRENTIAL RAIN IN EARLY SPRING, SHANXI

Using synoptic principles,satellite imagery and diagnosed physical quantities,this paper gives a comprehensive analysis of a torrential rain event that occurred in Shanxi province on Feb.20,2004.The results indicate the followings.(1) Its latitudinal circulation evolves quickly to a longitudinal one.(2) The water vapor in the rainstorm area is supplied mostly by a warm moist southwest jet stream in Bay of Bengal on the 700 hPa level and an 850 hPa southerly generated west of tropical low pressures in lower latitudes,and the location of the torrential rain is governed by the part of Shanxi where the southerly jet stream has extended to.(3) As shown in an analysis of the cloud imagery,there is a persistent cloud system of tropical low pressure near the Philippines during the torrential rain,which resembles cloud image features characteristic of large scale summer torrential rains.It is concluded that for the forecast of spring torrential rains in Shanxi,the water vapor and energy transport over lower latitude areas and movements of tropical low pressure cloud systems should be paid attention to besides circulation evolution.