华南一次典型回流暖区暴雨过程的中尺度分析

利用地面常规气象观测、FY-2E卫星TBB、多普勒天气雷达资料以及NCEP/NCAR 1°×1°再分析资料,分析了2013年5月8日发生在华南的一次暖区暴雨过程的中尺度特征。结果表明：（1）该过程发生在出海变性高压脊后部,较强的超低空东南急流遇到喇叭口地形作用形成地面辐合线产生辐合抬升是此次暴雨的启动机制;该过程未受冷空气影响,属于华南回流型暖区暴雨过程。（2）4个β中尺度对流系统（MCS）连续生成、东移发展是造成本次暴雨过程的直接原因,其中,第一个MCS持续时间最长达6 h,先前MCS消亡的同时在其西南侧又新生MCS,造成多个对流系统经过同一地区形成类似的＂列车效应＂。（3）不同于以往华南暖区暴雨个例水汽集中在850 h Pa或925 h Pa,此个例水汽主要来源于950 h Pa超低空东南急流,该急流使低层能量得以维持;中层小股干冷空气侵入为MCS发展和维持提供了有利条件;垂直螺旋度反映了深厚涡度柱与强烈上升运动的耦合,为暴雨发生提供了动力机制。（4）分析区域自动站风场资料可知,阳江-恩平一带夜间增强的东南风在有利地形下与陆地静风或东北风形成中尺度辐合线,使移入的小尺度对流云团加强并形成MCS,而MCS后侧出流与来自海洋上的东南气流形成新的中尺度辐合线又触发新的MCS,其后向传播特征明显。

Mesoscale analysis of a typical heavy rain event caused by returning flow in the warm sector in southern China

Data from conventional surface ohservations, FY-2E satellite, Doppler weather radar and NCEP/NCAR reanalysis with 1°× 1° resolution were used to analyze mesoscale features of a heavy rain event in the warm sector which occurred in Southern China on 8 May 2013, Results are as follows. （1） This event occurred at the back of high pressure ridge transformed over the sea. It is triggered by the ascending movement resulted from the surface convergence line caused by topographic effect where a strong extreme low-level southeast jet stream met hell mouthed terrain. The event hence belongs to a heavy rain by returning flow in the warm sector in southern China because it was not affected by cold air. （2） Successively originating, moving eastwards and strengthening of four β-mesoscale convective systems （MβCS）, in which the first MβCS lasted for 6 hour, are the direct cause that led to this event. A new MβCS originates in the southwest side of an earlier MβCS when it dissipates, which result in several going through the same area and hence forming a ＂train effect＂. （3） Being different from a heavy rain case in the warm sector in southern China earlier whose water vapor concentrates at 850 hPa or 925 hPa, the water vapor in this event comes mainly from the extreme low-ahitude （950 hPa） southeast jet stream, which maintains energy in the low-level. Intrusion of the weak dry and cold air in the middle level has provided a favorable condition for the development and maintenance of MCS. The large vertical helicity, which shows the coupling between deep vorticity column and strong ascending movement, has provided dynamic mechanism for occurrence of heavy rain. （4） Analysis of wind field data at the regional AWSs showed that the mesoscale convergence line formed by strengthening southeasterly located in Yangjiang to Enping area in the nighttime and ground northeasterly （or breeze） makes small scale convective cloud clusters strengthen to MCS. The new mesoscale convergence line is formed by