四川盆地西部两次暖区暴雨过程分析

Analysis of Two Warm-Sector Heavy Rain Processes in Western Sichuan Basin

利用地面、高空观测资料、卫星和多普勒雷达资料、ERA-Interim再分析资料,对2012年8月17日(12·08)和2017年7月16日(17·07)四川盆地西部两次暖区暴雨过程的环境条件、中尺度对流系统、雷达回波特征和动力抬升条件等预报着眼点进行了对比分析。结果表明:两次过程均出现在低层偏南暖湿气流和地面热低压之中,12·08暴雨发生在副高边缘,水汽输送条件更好,对流持续时间更长,17·07暴雨发生在高空低涡切变后部,高层冷平流使得位势不稳定更强,对流强度更剧烈;12·08暴雨中尺度对流系统沿副高外围自南向北缓慢移动,具有明显列车效应,其强回波质心高度较低,属于积状云为主的混合性降水,17·07暴雨中尺度对流系统在高空低涡后部偏北气流引导下自北向南快速移动,其强回波质心高度较高,属于积状云降水;地面辐合线为对流的发生发展提供了较好的动力触发条件,两次过程强降水均随着地面辐合线的生成而发生,且强降水中心出现在中尺度辐合线附近,并随着辐合线而移动。

By using the ground and upper-air observational data,Doppler radar data,FY-2 Esatellite observational data and ERA-Interim reanalysis data,the environmental conditions,mesoscale convective systems,the characteristics of Doppler radar reflectivity,the dynamic-lifted condition,and forecasting hints are analyzed and compared between two warm-sector heavy rain processes occurred on 17 Aug 2012 and 16 July 2017 in the Western Sichuan basin.The results show:(1)Both processes happened under the background of low-level warm-moist flows and ground thermal lows;the"12.08 "heavy rain occurred on the edge of the subtropical high pressure system;the moisture transport condition was better;and the heavy rainfall maintained longer.The"17.07" heavy rain happened behind the upper vortex-shear,the upper cold advection was more obvious,convective unstable energy was more abundant,and the convective system developed stronger.(2)The mesoscale convective system moved slowly on the edge of the subtropical-high pressure and had obvious train-effect during the"12.08 "heavy rain;the centroid height of the strong echoes was lower,so it was a kind of mixed precipitation dominated by cumulus clouds,but the mesoscale convective system moved quickly in the high-level north winds during the"17.07" heavy rain,and the centroid height of the strong echoes was higher,so it belongs to cumulus precipitation.(3)There was a good correlation between the heavy precipitation and the mesoscale convergence line:the ground convergence line provided the enough dynamically lifted condition for the heavy precipitation;both heavy precipitation events happened along with the generation of the convergence line and moved around the convergence line.