持续拉伸型中尺度对流系统发生发展与江苏暴雨分析

Analysis on persistent elongated convective systems and torrential rains in Jiangsu

利用自动气象站、卫星探测资料,NCEP/NCAR 1°×1°再分析资料等,从环流特征,动力、热力和水汽条件等对发生在江苏地区的两次梅汛期大暴雨过程的中尺度对流云团的发生、发展进行了分析。结果表明:这两次中尺度对流云团中均存在持续伸长型的中尺度对流系统(PECS),大暴雨区与T BB<-70℃区域有较好的对应关系,有利的环境场形成的高空辐散、低空辐合和强烈的上升运动是PECS发生发展的重要条件。PECS云团处于200 hPa高空急流入口区右侧、西南低空急流左侧(切变线南侧),呈西南—东北向线状排列,低层暖湿不稳定气流诱发中尺度云团的产生,气旋性涡度场对积云对流活动具有组织和增强作用。当正涡度向垂直方向发展时,附近产生强烈的垂直上升运动,对应着中尺度PECS云团的强烈发展。强烈的对流不稳定有利于中尺度对流系统的发展,也有利于触发暴雨产生。

By using intensive observation data from automatic meteorological stations, NCEP/NCAR global 1 °x 1 ° reanalysis data, satellite sounding data, etc, the genesis and evolution of the meso-scale convective cloud clusters which lead to the two torrential rains in the central of Jiangsu are analyzed in this paper. The result shows there exists persistent elongated meso-scale convective system （PECS） in the two meso-scale convective cloud clusters. Torrential rain areas tend to match with the areas with TBB below -70℃ , and the lower the TBB is, the stronger the precipitation is; the high-level divergence, low-level convergence and strong ascending motion provide favourable important conditions for the meso scale PECS＇ growth. The PECS cloud clusters are located in the right side of the entrance of the jet streamat 200 hPa, and in the left side of the jet stream in lower layer （the south of the shear line）, along the direction from southwest to northeast. The instable warm moist current in lower layer triggers the genesis of meso-β PECS cloud clusters, and the cyclonic vorticity builds up the cumulus convective activity. Mo- reover, the accumulation of vapor and instable energy are the important power source of the meso-scale PECS cloud clusters. The strong development of meso-scale PECS cloud cluster is caused by the strong vertical motion because of the vertical development of the vertical vortex nearby. The stratified instability of atmosphere helps develop meso-scale convective system and leads to torrential rain.