2015年5月19—20日两广地区暴雨过程数值模拟与诊断分析

Numerical simulation and diagnostic analysis of rainstorm over Guangdong and Guangxi region on 19-20 May 2015

利用NCEP/NCAR 1°×1°的6 h再分析资料和WRFV3.6模式对2015年5月19—20日两广地区一次暴雨过程进行数值模拟,并利用模拟结果对其成因进行诊断分析。结果表明:此次暴雨过程主要受500 h Pa上两槽一脊、副热带高压的共同作用以及850 h Pa上稳定存在的切变线及低涡的影响而成;WRF3.6模式能够较好地模拟出此次过程雨强及雨带分布;利用模拟结果诊断分析表明,副热带高压边缘的暖湿气流和高空大尺度西风槽的干冷气流的交汇,为本次暴雨的产生提供水汽条件;850 h Pa的低空切变线稳定存在于两广地区,并且低层强盛的急流建立起的水汽通道,为暴雨的形成提供了水汽条件和动力条件;本次暴雨过程的上升运动强盛且深厚,有助于低层暖湿空气向上输送,利于暴雨的发生、发展;螺旋度的中低层正中心、高层负中心的结构配置以及ξ_(mpv1)<0,ξ_(mpv2)>0的湿位涡分布表明大气处于极不稳定的状态,有利于对流的发展。

The 1°×1° NCEP/NCAR reanalysis data with temporal resolution of 6 hr and WRF 3.6 model were employed to simulate a heavy rain event in the region of Guangdong and Guangxi during the May 19-20, 2015. The simulation results were used to diagnosis its causes.Analysis results show that the torrential rain event is mainly affected by the interaction among the system of two troughs and one ridge, the subtropical high on 500 hPa, and the shear line and low vortex persistently existed at 850 hPa. WRF3.6 model can well simulate the rainfall intensity and the rainband distribution. Diagnostic analysis with simulation result shows that the convergence between the warm moist air flows on the edge of the subtropical high and the dry and cold airflow from large-scale westerly trough have provided the moisture condition for this heavy rain event. The vapor channel that was established by the low-level shear line persistently existed in the region of Guangdong and Guangxi and strong jet on 850 hPa have also provided for the moisture conditions and dynamic conditions. The upward movement in the heavy rain event is strong and deep, which contributed the transportation of warm moist air upward and the occurrence and development of heavy rain. The configuration of positive center in the low level and the negative center in the high level of spiral degrees, and the distribution of wet vortex with ξmpv1 < 0 and ξmpv2 > 0 also showed that the atmosphere is in an unstable state and was conducive to the development of convection.