2012年白银市一次局地暴雨天气过程诊断分析

Analysis of the formation of a Local Midsummer Rainstorm in 2012 in Baiyin

利用MICAPS系统中常规地面和高空资料、T639数值预报产品以及FY-2卫星云图资料，对2012年8月17日白银市局地暴雨天气过程的成因进行了诊断分析．结果表明：（1）高空低槽东移南压是暴雨产生的大尺度环流背景，低层切变线、低涡是暴雨发生的触发机制，低空显著西南气流为暴雨过程建立了水汽输送通道；（2）低层水汽辐合形成比湿为11～13g／kg高湿区，为暴雨提供了充沛的水汽条件；（3）低层正涡度中心、散度上正下负的配置，强上升运动为暴雨提供了动力条件；（4）K指数〉40℃、θse高能舌使得大气不稳定层结增强，为暴雨的出现提供了热力条件和能量条件；（5）多个中启尺度对流云团沿700hPa低涡切变发展合并北上，是此次局地暴雨产生重要原因．

Based on the conventional surface and upper air data of the MICAPS system, the numerical forecast product T639,and FY-2 satellite cloud picture,the analysis of the formation of a Local Rainstorm were made,which hit Baiyin,Gansu on August 17,2012. The results show that,eastward and southward high-altitude low trough was the large-scale circulation background, the low-level shear line and vortex were the trigger mechanism of the rainstorm, and significantly southwesterly low-altitude airstreams estab- lished the water vapor transport channel for the rainstorm process; the low-level moisture convergence formed the high humidity area of specific humidity 11--13 g/kg,providing abundant water vapor conditions for the storm; low level vorticity center, positive up and negative-down divergence, and strong upward movement provided the dynamical condition for the storm;the K index （〉40℃） and the high energy tongue of 0se made atmospheric stratification more unstable,providing thermal conditions and energy con ditions for the emergence of the rainstorm; multiple fl-scale convective clouds merged and moved northward along the 700 hPa vortex shear,being an major reason for the generation of the storm.