2011年“7·25”山东乳山特大暴雨成因分析

利用常规资料、地面加密资料、多普勒雷达资料和ＮＣＥＰ再分析资料等,对2011年7月25日发生在山东省乳山市一次超历史极值的特大暴雨过程进行分析。结果表明：本次特大暴雨是由高空西风槽、低层切变线与副热带高压边缘的低空急流共同影响所致；由低层前期强盛的低空偏南暖湿气流输送使半岛上空低层高温高湿,形成上干冷下暖湿的对流性不稳定层结；近地面向岸风的侧向辐合产生气旋式切变线，是本次暴雨的启动机制，大暴雨的分布与地面辐合线的走向基本一致。此外，半岛上空超低空偏南急流的加强，使中尺度切变线北抬，进而受乳山倒喇叭口地形影响，发展成了中气旋，产生了强降水超级单体风暴。而强降水超级单体风暴造成的短时强降水，是本次暴雨致灾的重要原因。

Cause Analysis of a Torrential Rainfall in Shandong Rushan on July 25, 2011

Based on regular observation data,surface intensive observation data,Doppler radar data,as well as NCEP reanalysis data,an excessive rainfall over historical maximum occurred in Rushan on July 25,2011 was analyzed.Results showed that: the westerly trough,low level shear line,and the low level jet on the edge of subtropical high were the main causes of the excessive rainfall.The previous strong southerly warm and hot flow transportation made the low level air of Shandong peninsula high temperature and humidity and led to the convective unstable stratification with hot and humid in lower and cold and dry in upper.In surface,the cyclonic wind shear formed by the lateral convergence of the on-shore wind was the initiating mechanism of the rainfall,the distribution of the rainfall consisted with the ground convergence line.Furthermore,intensification of ultra-low level jet over the Shandong peninsula led the mesoscale shear line to rise northward,and a mesoscale cyclone developed under the influence of the inverted trumpet-shaped topography,then a heavy rainfall supercell storm generated.The short-time heavy rainfall caused by the supercell storm was the primary cause of this rainstorm-induced disaster.