黔西南一次低涡切变型暴雨的中尺度分析

Mesoscale Features of a Rainfall Triggered by Low-vortex Shear in the Southwest of Guizhou Province

利用常规观测资料、FY-2E TBB资料、自动站降水资料及1°×1°NCEP再分析资料,对发生在黔西南2014年6月9日的暴雨过程进行了分析,结果表明:本次暴雨过程主要是由低涡切变造成的,低涡切变东南移的过程中,黔西南地区低层辐合明显加强,触发了中尺度对流系统的发生发展。暴雨过程强度大,持续时间短,有典型的中尺度特征。两个大暴雨中心是由两个MCS产生的,都是沿低涡前侧的切变线移到暴雨中心上空的,降水主要出现在MCS的中部冷云区及梯度大值区。雷达回波资料显示此次过程是由多个对流单体发展、合并,形成混合性片状回波,回波在东南移的过程中逐渐减弱消散。暴雨发生前及发生时整个黔西南地区中低层有强烈的辐合上升运动,中高层为下沉运动,黔西南低层的θse为高值区且等值线密集,整层湿层深厚,动力强迫上升运动加强了低层能量和水汽的向上输送,促使中尺度对流系统的发生发展。

Based on the Conventional observation data, satellite data, automatic station precipitation data ,and NCEP/NACR reanalysis data,the rainstorm process during 20：00 9 June to 20：00 10 June in the southwest of Guizhou province was analyzed. The results are as follows：The rainstorm process is mainly caused by the low vortex shear. Low-level convergence improved remarkably around the southwest of Guizhou province trigging the development of the meso-scale convective system when the low vortex shear shift to southeast. The surface rainfall obviously showed meso-scale spatial and temporal distribution feature. low vortex cloud inspired the mesoscale convective system, precipitation emerged mainly in the center in the cluster area or edge of MCS. when and before the storm occurring in the whole southwest of Guizhou province region. There was a strong convergence ascending motion in the lower level, the high-level sank,high divergence, low-level convergence,the wet layer deep, when the air flow to the most powerful formed a cyclone type circulation in the vertical direction, the vorticity is increased obviously, dynamic force upward movement strengthen the lower energy and water vapor upward transportratio. As the shear line shift to the southeastern, water vapor convergence weaken, low level sank, the unstable layer decreases ,and obvious downward extension of neutral layer, the mesoscale convective system weakens and shifted to southeastern.