2018年8月石家庄市两次强降水分析

Analysis of Two Strong Rainfall Processes in Shijiazhuang City in August 2018

基于高时空分辨率的地面自动气象站资料、多普勒雷达资料、VDRAS反演资料及NCEP再分析资料等,采用中尺度分析和动力学论断方法对2018年8月11、12日两次强降水进行触发机制和中尺度对比分析。结果表明,"8.11强降水"与"8.12强降水"均发生在副热带高压外围西南暖湿气流中,"8.12强降水"伴有蒙古国分裂南下冷空气。强降水对应的雷达反射率因子回波为一条40dBz及以上回波带,回波移动方向与回波带轴向一致,形成"列车效应",径向速度图中风向辐合及"逆风区"与强降雨时段配合较好。强降水触发机制为地面辐合线、露点锋和低压系统;大气层结表现为低抬升凝结高度和自由对流高度、较强对流有效位能和深厚的暖云层;低空急流利于水汽和能量的输送。

Based on the ground automatic weather station data with high temporal and spatial resolution,Doppler radar data,VDRAS and NECP(1°×1°)reanalysis data,the trigger mechanism and the mesoscale features of two successive short-time strong rainfall processes occurred in Shijiazhuang City in August 2018 were analyzed by mesoscale analysis and dynamics method.The conclusions are as follows.These processes both occur against the background of the humid,warm and southwest airflow around the subtropical high.Additionally,only the rainstorm on August 12 is affected by the cold air from Mongolia.A 40 dBz echo strip on Doppler radar image is found over the precipitation areas for both processes,forming the"train effect".The wind direction convergence area and the"windward area"on the radial velocity image are good matched with the period of intense precipitation.The ground convergence line,dew point front and low-pressure system trigger both precipitation events.The ambient conditions are characterized by low lifting condensation level and free convection level,strong convective available potential energy,deep warm layer and warm advection.The low-level jet facilitates water vapor and energy transport.