2012年盛夏山东西部一次短时强降水天气的形成机制

摘要

利用常规观测资料、自动站加密观测资料、卫星云图和雷达资料，对2012年7月4日山东省西部一次短时强降水的天气形势、物理量条件、云图和雷达回波特征进行分析。结果表明：在有利降水的大尺度天气系统背景下，低层冷空气和中尺度天气系统造成了本次短时强降水天气；低层925 hPa和1000 hPa的充沛水汽和辐合上升运动有利于强降水天气的发生，正涡度中心对应强降水中心；地面辐合线和低压环流造成本次短时强降水天气；中尺度对流云团和地面中尺度系统相对应，其位置和维持时间与强降水的落区和时间基本一致。雷达组合反射率因子＞45 dBZ的强回波区与强降水落区基本吻合；雷达平均径向速度产品逆风区中辐合流场的出现和维持及回波顶高的上升对应地面中尺度气旋式环流的形成和维持；逆风区中辐散流场的出现和维持及回波顶高的下降，对应地面中尺度气旋式环流的减弱；短时强降水出现的初期，垂直累积液态水含量出现了一个峰值，峰值出现时间提前于较强降水时段。%The paper analyzed the weather situation,physical quantity condition and the characteristics of satellite cloud images and ra-dar echo on July 4 2012 in western Shandong Province by using conventional observation data,intensive observation of automatic weath-er station as well as satellite images and radar data.The results show that this short-term strong precipitation was caused by the lower cold air and the mesoscale weather system under the background of the propitious large-scale weather system.Abundant water vapor and the strong convergence ascending motion on the level of 925 hPa and 1 000 hPa were conducive to the occurrence of strong precipi-tation.The positive vorticity center was corresponding to the strong precipitation center,and the surface convergence line and cyclonic circulation touched off the short-term strong precipitation.The satellite cloud images and radar data revealed the occurrence and de-velopment of the mesoscale weather system.The position and the maintain time of the mesoscale convective cloud cluster were consist-ent with the mesoscale system,and the same as the short-term strong precipitation.Strong radar echo region with composite reflectivi-ty factor more than 45 dBZ corresponded with the area of the short-term strong precipitation.Appearance and maintenance of the con-vergence flow field in radar radial velocity product were associated with the mesoscale cyclonic circulation,as well as the echo top height rising.While appearance and maintenance of the divergence flow field,and decline of the echo top were associated with weake-ning of the mesoscale system.The peak of the vertical accumulated liquid water contend appeared at the early stage of the short-term strong precipitation,and the peak value occurred before the stronger precipitation.