2016年7月18—20日湖北省特大暴雨过程的中尺度特征分析

Analysis of Mesoscale Characteristics of Torrential Rainfall in Hubei Province During 18—20 July 2016

利用多种常规和非常规观测资料诊断分析了湖北2016年7月18—20日特大暴雨过程的降水特点以及中尺度对流系统(MCS)的发生发展特征和环境场条件,结果表明:此次特大暴雨过程具有很强的极端性,分为梅雨锋南侧暖区降水和梅雨锋面降水两个阶段,都具有较为极端的水汽条件。第一阶段在地面风场辐合的作用下触发了初生对流单体,西南低空急流出现脉动,湿层的增厚促进了强雷暴的发展。新生单体在雷暴上游生成,迅速并入强雷暴,后向传播是其稳定少动的重要原因之一。强盛阶段,强雷暴具有暖云低质心的特征,低层垂直风切变与雷暴偏北风出流的方向配置、中气旋的出现都促进了上升运动,促使强雷暴长时间维持,造成了马良站连续数小时出现高强度降水。第二阶段,环境风平行分量远大于垂直分量,促进了东北—西南向平行层状MCS(PS型MCS)的形成。具有多单体依次排列的特征,新生单体在系统西南侧地面辐合线的作用下不断生成发展,使得PS型MCS增强维持,移动缓慢。马良站受到PS型MCS对流线和西北侧层状回波的影响,小时强降水明显较第一阶段偏弱。

Based on various conventional and unconventional data,precipitation characteristics,generation and development of the mesoscale convective system(MCS)and environment conditions of the torrential rainfall in Hubei Province during 18—20 July 2016 are analyzed in this paper.The results show that this torrential rainfall process was highly extreme.The process consisted of warm area precipitation in the south of Meiyu front and Meiyu frontal precipitation.There were extreme water vapor conditions in the two periods.In the first stage,the primary convective monomers were triggered by the convergence of the ground wind field.The southwest low-level jet showed pulsation.The thickening of the wet layer promoted the development of strong thunderstorm.The new monomers formed in the upper reaches of thunderstorms,and rapidly merged into strong thunderstorm.The backward propagation was one of the important reasons for its stable and moveless.In the strong phase,the strong thunderstorm had the characteristics of warm cloud and low center of mass.The configuration of vertical wind shear in the low layer and the northerly outflow of thunderstorm and the appearance of mesocyclone both promoted the upward movement,causing the long-term maintenance of the strong thunderstorm.It caused high intensity precipitation at Maliang Station for several hours.In the second stage,the line-parallel layer-mean wind component was bigger than the line-perpendicular,which promoted the formation of northeast-southwest parallel stratiform MCS.It had the characteristics of multiple monomers arranged in sequence,and the nascent monomers were continuously generated under the effect of the ground convergence line on the southwest side of the system.Their development made the parallel stratiform MCS enhanced and maintained.The Maliang Station was affected by the parallel stratiform MCS convection line and the northwest side layered echo,and the hourly precipitation was significantly weaker than in the first stage.