海陆风环流在天津2009年9月26日局地暴雨过程中的作用

The Role of Sea-Land Breeze Circulation in Local Convective Torrential Rain Happening in Tianjin on 26 September 2009

利用常规天气资料、地面加密自动站资料、天津中尺度模式产品资料以及卫星云图和多普勒雷达等资料,对2009年9月26日出现在天津地区的局地暴雨过程进行天气学、动力学诊断分析和中尺度分析。结果表明,本次暴雨的天气尺度主要的影响系统是500 hPa高空槽,中尺度系统是由海陆风环流形成的地面中尺度辐合线。降水前天津市具有较好的热力不稳定条件,较好的能量储备,有利的动力条件,一定量级的水汽辐合,边界层的东风将渤海的水汽输送至天津市,是本次过程的主要水汽来源。天气尺度的积云对流与海风锋的碰撞触发不稳定能量的释放,引发第一阶段的强降水,边界层东风急流再度加强所产生的抬升效应引发第二阶段的降水。中尺度切变线通过提供带状辐合上升运动起着胚胎和组织积云对流的作用,使得降水回波和对流云团沿中尺度切变线发展、加强和移动,产生了明显的列车效应,导致了这场历史罕见的秋季局部暴雨过程,也充分凸显出海陆风环流对本次暴雨的重要作用。

A local torrential rain process occurring in Tianjin on September 26,2009 is diagnosed and a mesoscale analysis of it is performed,based on the conventional and surface densified automatic station observations, data of mesoscale model of TMMB,satellite cloud pictures and Doppler radar data etc.The results show that the heavy rain occurs when the large-scale circulation pattern is adjusted from meridional to zonal.The trough of 500 hPa is the major synoptic scale system in this event,while the main mesoscale systems are surface mesoscale convergence line,humidity frontal zone and sea breeze front visible in Doppler radar imagery,which are driven by sea-land breeze circulation.And a fully developed thermal instability before the occurrence of the torrential rainfall has being established,the synoptic scale environment has considerable energy storage,favorable dynamic condition and moisture convergence from the Bay of Bengal at 700 hPa and the sea to the east of Tianjin at 850 hPa.The collision of synoptic system driven cumulus convection and sea breeze front triggers the release of instable energy,resulting in the heavy precipitation of the first period.The strong easterlies in the boundary layer indicate the essential role of sealand breeze circulation in this torrential rain event.