高原涡与西南涡相互作用暴雨天气过程的诊断分析

利用动力诊断方法,对2008年7月20~22日高原低涡与低层西南低涡相互作用引发西南低涡强烈发展和四川大面积特大暴雨天气发生机理进行了诊断分析。分析表明：高原涡与西南涡涡心之间的纬向距离在5个纬度的时候,两者上升气流都在500 hPa以下,当两者继续东移,在经向上耦合的时候,二者同时得到发展,西南涡中心的上升气流达到300 hPa,而高原涡中心的上升气流突破200 hPa;西南涡在低层出现初期,在一定程度上制约了高原涡的发展,随着两者在经向方向发生耦合,上下涡度平流不同造成垂直差动,将激发500 hPa以下的上升运动与气旋性涡度加强,使得500 hPa与700 hPa涡心正涡度值的增大近1倍。并且涡前的正涡度变率使得高原涡发展并东移,待垂直耦合后,高原涡与盆地涡相互强迫作用促使气流上升运动加强也是导致高原低涡与西南低涡共同发展的一种机制。

Diagnostic Analysis of Vorticity in a Heavy Rain Event under Interaction of Plateau Vortex and Southwest Vortex

With the momentum diagnosis method, an analysis is made of the interaction between plateau vortex and southwest vortex during a heavy rain event in Sichuan on 20 to 22 July 2008. The results show that when the latitudinal distance between plateau vortex center and southwest vortex center was 5°, the updrafts in both vortexes were confined within 500 hPa; when moved eastward and coupled longitudinally, they both developed, with the updraft of the southwest vortex center reached 300 hPa and that of the plateau vortex center reached 200 hPa. The southwest vortex restricted the development of the plateau vortex in some way at the early stage when it appeared in the lower atmosphere. When they were coupled longitudinally, the vertical difference caused by the different vorticity advections between the upper and lower levels excitated the updrafts under 500 hPa and strengthened cyclone vorticity, and then the positive vorticity at 500 hPa and 700 hPa increased by two times The change rate of positive vorticity facilitated the plateau vortex to move eastward. After coupled longitudinally, the interaction of the plateau vortex and basin vortex strengthened the updrafts. As a result, the plateau vortex and southwest vortex influenced each other and developed together.