高原低涡移出高原的观测事实分析

应用天气学、统计学原理,结合TRMM资料,分析了1998—2004年5—9月移出高原的低涡的活动特征。结果指出:6—8月是高原低涡移出高原影响中国东部天气的主要时段,它与高原低涡在高原上的活动特征及西南低涡移出高原特征均不同;移出高原的高原低涡的涡源主要在曲麻莱附近、德格附近,这与高原上产生低涡的涡源不同;移出高原的高原低涡的移动路径多数是随低槽的活动而向东、向东南移动,这与高原低涡在高原上多数是沿切变线移向东北不同,高原低涡移出高原后,不仅影响中国的范围广,还可能影响到朝鲜半岛、日本;高原低涡移出高原后涡的强度、性质会有变化,在高原以东活动时间长(≥36 h)的高原低涡,移出高原前多数为暖性低涡,移出高原后多数为斜压性低涡,低涡加强、多数可产生暴雨、大暴雨;高原低涡移出高原后移到海洋上,往往因下垫面不同而变化,出海后都有降水加强、多数位势高度下降的现象;移出高原后的高原低涡因东面海上热带气旋活动而少动,与其南面热带气旋活动相向而行,因季风低压少动而少动的现象。

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 Tibetan Plateau during May to September in 1998-2004 are analyzed base on the TRMM data by using the synoptic/statistic methods.The following movement characteristics 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 Tibetan Plateau and then influencing weather in eastern China is from June to August,and their movement characteristics after moving out the plateau differ from those before moving out,and also from those of Southwest low vortices.(2) The major origin of the plateau vortices which move out the Tibetan Plateau is in the vicinity of Qumalai and Dege,different from the origin of plateau vortices which remain over the plateau.(3) The plateau vortices moving out the plateau are usually move eastwards or southeastwards 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 China,but also in the Korea peninsular and Japan.(4) The characteristic and intensity of the vortices will change after moving out 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,and 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 central geopotential height decrease;the vortex may remain stationary,when there are activities of tropical cyclones in the East China Sea or its vicinity;it moves southwards when there is the tropical cyclone in the South China Sea;and it may move slowly or remain stationary when the monsoon low system is inactive in India and the Bay of Bengal.