低涡与急流对“04.9”川东暴雨影响的分析与数值模拟

Analysis and Numerical Simulation for Effects of Vortex and Jet Stream on Heavy Rain in East Sichuan in September 2004

2004年9月3日～5日川东出现了大范围的强暴雨过程,本文分析了这次暴雨过程的云图特征和环流形势,并利用MM5中尺度数值模式对本次暴雨进行了二重嵌套模拟,分析及模拟结果表明,本次降水过程与中尺度云团、高低空急流和对流层中低层涡旋活动密切相关,同时还与副热带高压活动和'桑达'台风活动相关.盆地涡出现在低空急流的左侧,而川东强降水发生在高空急流的南面、低涡东南侧与西南低空急流大风出口区之间.盆地正涡度维持有利于盆地上空垂直上升运动的发展和维持,对暴雨的发生提供了动力条件.垂直上升运动是高低空急流和盆地涡联系的纽带,也是盆地涡动力驱动的结果.分析结果还表明,西南低空急流在暴雨出现前建立,暴雨和盆地涡同时出现,而暴雨、低空急流和盆地涡几乎同时减弱.高空急流在过程前和过程中是逐步加大,当高空急流出现剧减时,预示暴雨即将结束.

We have analyzed the effects of vortex in the basin and jet stream on heavy rain in the east of Siehuan province in September 2004, and have done numerical simulation. The results show the process of precipitation is related to mesoscale cloud mass, jet stream and vortex activities in mid- and lower- levels, at the same time, and along with to activities of subtropical high pressure and “SHANG DA” typhoon. The vortex in Sichuan basin appeared in the left of lower- jet stream, and the heavy rain in the east of Sichuan occurred in the south of upper level jet stream, there exits strong south-east lower jet stream to south-east of low vortex. Maintaining of positive vortex in the basin is benefit to the development and lasting of the vertical ascending movement over the basin, and provided dynamic condition for heavy rain. Vertical ascending movement was the ligament linking jet stream and basin vortex as well as dynamic driving result in the basin. The south-west jet stream had built before the heavy rain appeared, and heavy rain and basin vortex appeared almost at the same time, as well as the heavy rain, low jet stream and basin vortex weaken together. The high jet stream was progressively increasing before and during the process of the precipitation. When the upper level jet stream weakened, heavy rain was ending.