2008年7月威海市暴雨过程成因分析

The Causes of Heavy Rainfall in Weihai in July 2008

利用美国环境预报中心(NCEP)/国家大气研究中心(NCAR)1°×1°的6h再分析资料和常规观测资料,对2008年7月19日和24日威海市两次暴雨过程的形成机制进行了天气学诊断分析,结果表明,中高纬度欧亚上空阻塞高压的建立、加强,使得500hPa高度上西风锋区南压,冷空气南下,有利于山东半岛暴雨的加强;造成两次暴雨的天气系统高空为冷涡,低层为切变线或低压;冷空气和暖湿气流在山东半岛附近交汇,使暴雨产生和发展;来自东海-黄海中部的水汽对强降水的维持起重要作用;切变线和低涡暴雨都是低空为散度辐合,高空为散度辐散,但辐合中心高度不同,两类系统的垂直上升运动都到达200hPa,这种配置是暴雨产生的动力条件;山东半岛高能、高湿区的存在是暴雨形成的热力条件。

By employing the NCEP/NCAR reanalysis data and routine observation data, the causes of heavy rainfall in Weihai on 19 and on 24 July 2008 are analyzed. It is shown that the establishment and the maintenance of the blocking anticyclone over Northern Asia lead to the southward movement of the westerly frontal zone and the dry cold air. The changes of the general circulation enhance the torrential rain over Weihai. The rainstorm processes are the result of the joint action of the high-level cold vortex and the low-level shear line or low pressure. It is also revealed that once the dry cold air meets the moist warm air over Shandong Peninsula, the heavy rainfall develops. The vapor comes from the East Sea and Yellow Sea. The vapor convergence comes into existence in Shandong Peninsula and plays a crucial role in the maintenance of the strong precipitation. In the period of rainstorms, the convergence in the underlying bed and the divergence in a high-level are characteristic of a divergence distribution. The convective ascending movement and the strong updraft found over 800 hPa and below 400 hPa provide a favorable dynamic condition for the rainstorms. The sufficient high energy of the potential pseudo-equivalent temperature θse in the rainfall region, the energy frontal zone in the northwest of the high energy area and the moisture provide the thermal condition for the formation of heavy rainfall.