长江中下游一次非典型梅雨锋中尺度暴雨过程的分析研究

利用T10 6物理分析资料、地面与高空加密观测资料和TBB资料对 2 0 0 1年汛期一次非典型的梅雨锋中尺度暴雨过程进行天气学和动力学诊断分析 ,并与 1998年典型的梅雨锋中尺度暴雨过程作一些比较。首先分析了该次暴雨过程的大尺度背景场 ,发现与 1998年典型的梅雨锋形势不同的是 ,5 0 0hPa环流形势表现为贝加尔湖地区是阻塞高压 (阻高 ) ,南海季风涌形式不明显 ,南亚高压位置偏东南 ,高空辐散气流较弱。接着对该暴雨系统的结构进行诊断分析 ,揭示了该非典型梅雨锋中尺度暴雨系统的三维结构 ,包括各物理量如涡度、散度、假相当位温、水汽的通量以及湿位涡等的结构特征。分析表明 ,总体来说 ,该次暴雨过程的强度要比 1998年典型的梅雨锋暴雨要弱 ,相应的各物理量的三维结构与 1998年典型的梅雨锋中尺度暴雨系统的三维结构相比有明显差异。

A CASE STUDY ON MESOSCALE HEAVY RAINFALLS WITHOUT MEIYU FRONTAL IN THE RAIN SEASON OF 2001

One case of mescoscale heavy rainfalls without background of evident Meiyu front in the raining season of 2001 was analyzed by both the synoptic and dynamic methods, utilizing data of T106, GMS TBB Data and upper & surface observation data from the field experiments in 1998. The analysis results were compared with that of the typical heavy rainfall system with background of Meiyu front. At first the large-scale and synoptic-scale condition of this heavy rainfall process was investigated and revealed that the flow of 500hPa features with a blocking high in the region of Baikal which lasted about three days, there didn't exist distinct strong southerly wind in the region of South China Sea at low level as heavy rainfall in the raining season of 1998 did, the Subtropical High made a eastern and southern excursion compared with the normal position over the same period, and the divergence flows in the high level were weak. Then, the mescoscale structure characters of the intensive convective system were revealed by analyzing observation data, which indicated that this mesoscale intensive convective system without background of evident Meiyu front showed some different 3D characters compared with the 1998 case with evident Meiyu front background, including the variables of vortex, divergence, equivalent potential temperature, moist potential vorticity etc. Finally this case of heavy rainfalls was explored by means of MPV diagnose and some significant conclusion were drawn for further discussion.