一次暴雨过程中两个降水阶段的差异分析

Diagnostic Analysis in the Difference between Two Stages of a Torrential Rain Process

利用NCEP格点再分析资料和WRF模式输出的高分辨率资料、自动站降水资料、雷达资料对2010年8月14 16日发生在重庆的一次大暴雨过程进行了数值模拟和诊断分析。结果表明:此次暴雨过程分为两个阶段,降水系统主要有两个:第一阶段的主要降水系统是低空切变线;第二阶段的主要降水系统是低空切变线和850 h Pa西南低涡,并且第二个阶段内的降水量较大、持续时间也较长。风垂直廓线的时间演变表明,暴雨发生、发展过程中,中低层强西南风风速的下传和低层切变辐合的存在对中尺度对流系统的增强有着重要的作用;数值模拟分析显示,第一阶段,弱的冷平流影响暴雨区,在低空切变线的作用下,引起气团在水平方向辐合,触发中尺度对流系统的发生、发展;第二阶段,中高层强的冷空气倾入降水区,850 h Pa低涡生成后东移至重庆东北地区,其低涡附近的垂直上升运动与700 h Pa切变线附近的上升运动相耦合,强迫抬升中低层暖湿空气并再次触发降水区域的中尺度对流系统。

With NCEP reanalysis data、WRF model simulated high resolution output data、automatic station precipitation data and radar data、radar data,a diagnosing analysis and numerical simulation is made of a heavy rain in Chongqing from 14 to 16 August 2010. The result indicate that the heavy rain processes which divided two stages,has two precipitation system : the first stage of the main precipitation system is the lowlevel shear line; The second stage of precipitation system are the lowlevel shear line and 850 hpa of southwest vortex,and the second stage of the rainfall is larger and has longer duration. The vertical wind profile of time evolution shows that the heavy rain in the process of development,strong low- level southwest wind speed downlinking and the existence of the low- level shear convergence has a very important role for enhancement of the mesoscale convective system. The numerical simulation analysis shows that in the first phase of the heavy rain process,weak cold advection influence the rain area,under the impact of low- level shear line,cause air mass convergence in horizontal direction and trigger the mesoscale convective system development; in the second stage,the high- level strong cold air poured in precipitation area,the vertical ascending motion near the lowvortex coupling interaction the upward movemen near 700 hpa shear line after the 850 hpa vortex eastward to Chongqing northeast area,which forces the low- level warm moist air to lifting and triggers the mesoscale convective system again.