OBSERVATIONAL ANALYSIS ON THE MOVEMENT OF VORTICES BEFORE/AFTER MOVING OUT THE TIBETAN PLATEAU

Characteristics of the activities of the plateau low vortices moving out the Tib etan Plateau during May to September in 1998-2004 are analyzed base on the TRMM data by using the synoptic/statistic methods. The following movement characteris tics and observational facts of the intensity change of the plateau low vortices moving off the Tibetan Plateau have been obtained. （1） The major time period in a year for plateau low vortices moving out the Ti b etan Plateau and then influencing weather in eastern China is from June to Augus t, and their movement characteristics after moving out the plateau differ from t hose before moving out, and also from those of Southwest low vortices.  （2） The major origin of the plateau vortices which move out the Tibetan Platea u is in the vicinity of Qumalai and Dege, different from the origin of plateau vo rtices which remain over the plateau. (3) The plateau vortices moving out the plateau are usually move eastwards or so u theastwards with troughs, while those remaining over the plateau frequently move northeastwards along the shearline. After moving off the plateau, the plateau vortex may not only impacts weather in a large stretch of downstream areas in Ch ina, but also in the Korea peninsular and Japan.（4） The characteristic and intensity of the vortices will change after moving o ut the plateau. The vortices, which remain active for 36 h after moving out, are mostly warm low vortices before and mostly become baroclinic after moving out, a nd then strengthen, bring about torrential rain or heavy torrential rain. （5） After moving out the plateau, the vortex may change its behavior: When moving over the sea surface, its precipitation will mostly strengthen, and its centr al geopotential height decrease; the vortex may remain stationary, when there ar e activities of tropical cyclones in the East China Sea or its vicinity; it move s southwards when there is the tropical cyclone in the South China Sea; and it m ay move slowly or remain stationary when the monsoon low system is inactive in I ndia and the Bay of Bengal.