与低空急流相伴的暴雨天气诊断分析

Diagnostic study on the torrential rains coupling with the lower southwest jets in Yunnan

摘要: 对1998年5月～2002年5月7例与低空急流相伴的云南全省性暴雨过程进行了合成诊断分析.结果表明:临近暴雨发生时,西南低空急流的形成应是云南暴雨产生的主要原因,暴雨天气通常出现在低空急流北侧风矢呈气旋性弯曲、风速递减的梯度十分明显的区域内;低空急流对于水汽和能量的输送起非常重要的作用,它一方面为暴雨的产生提供了所需要的大量水汽,另一方面又使得暴雨区低层大气增湿增暖,从而引起对流不稳定加强,为暴雨的发生提供大量的不稳定能量.湿位涡分析表明,暴雨发生前,冷暖空气在云南交汇,使大气温湿结构发生变化,θe等值面坡度加大,当低空急流移向对流不稳定区时,便有气旋性涡度剧烈发展,导致暴雨天气的发生.

Abstract: Seven cases of the torrential rain coupled with the lower jets during Feb.1998-May,2002 in Yunnan are composite analyzed.The results show that the lower south-west jets is the main cause of torrential rain;Torrential rains usually occurred in the north of the lower jets where are characterized by cyclonic winds and lapse of wind speed;lower jets have an important effect on the transportation of the moisture and energy for the torrential rain.Some useful results by using the concept of moist potential vorticity are also obtained in this paper.