低层偏南气流对一次暴雨过程的动力作用分析和数值模拟

Analysis on Dynamic Effects of Low-Level Southerly Airflows on One Rainstorm Process and the Numerical Simulation

利用常规观测资料和NCEP再分析资料,对2010年7月22—25日四川盆地西部出现的一次暴雨过程进行了诊断分析。结果表明:暴雨出现在对流层低层南海至四川盆地一直维持偏南气流的环流背景下,暴雨与这支偏南气流的风速演变密切相关,降雨强度随南风气流的增强而增强,南风气流增强所形成的风速辐合及正涡度平流是暴雨的主要动力触发因子,暴雨与低层辐合和正涡度平流区域有很好的对应关系。WRF数值模拟试验进一步表明:850 hPa层3 h风速演变对中尺度对流系统的发展具有很好的指示意义,在3 h风速增大区域的下风方,未来3 h对流云团将迅速发展;盆地西部形成的气流辐合与其西侧的高原地形密切相关。

By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22--25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low-level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty con- sistent with the low-level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that： the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely re- lated to the topography of plateau.