“8.19”西北东部大到暴雨诊断分析和数值模拟

Diagnosis and Numerical Simulation of "8.19" Heavy Rain in the East of Northwest China

利用MICAPS系统T213资料、NCEP再分析资料及实况观测资料,对2004年8月19日发生在西北地区东部的暴雨天气过程的大尺度环流背景和物理量场进行分析发现:这次暴雨天气过程中西太平洋副热带高压有一次明显的西伸,是一次较典型的副高西北侧西南气流型暴雨。降水水汽主要来自南海和孟加拉湾,中低层的水汽输送十分充沛,并在甘肃河东和宁夏形成辐合。运用三重嵌套的中尺度数值预报模式MM5,对这次暴雨过程进行了两种方案的高分辨率数值模拟,结果表明,运用四维资料同化后的方案在形势和降水预报方面优于未进行资料同化的方案。

Based on T213, NCEP/NCAR reanalyzed and conventional observation data, the general circulation and the physical field of the heavy precipitation on August 19 are analyzed at first. The result shows that this event is a typical southwest flow type caused by West Pacific subtropical high extending westward. The moisture mainly moved from the Bay of Bengal and the South China Sea. The moisture transport in low-and medium-level is very strong and the convergence occurs in Ningxia and east of Gansu Province. Second, with the threeway nested high resolution mesoseale NWP model MM5 to simulate this event by two methods, the four-dimensional data assimilation model is proved to be of quite good quality in circulation and precipitation forecasts.