一次突发性特大暴雨的中尺度分析和诊断

A mesoscale analysis and diagnose of an extreme bursting torrential rain

利用常规探测资料、TBB资料和NCEP分析资料,对2008年5月27日发生在沅陵西北部的一次突发性特大暴雨天气过程进行了中尺度分析和诊断。结果表明:这次特大暴雨是在有利的大尺度环流背景下发生的,低空西南急流为暴雨区带来了丰富的水汽和不稳定能量;产生暴雨的中βCS云团由两个对流云团合并而成,具有椭圆形结构特征,长时间维持少动,强降水出现在中βCS云团发展最旺盛的地方;在尺度分离的流场上,特大暴雨出现在850 hPa和700 hPa的两条中尺度辐合线之间的低层辐合区内;这次暴雨与暴雨区上空对流层中低层正垂直螺旋度、高层负垂直螺旋度中心的分布和增大减小变化密切相关;非地转湿Q矢量激发的次级环流的存在有利于不稳定能量的释放,促进暴雨发生发展;暴雨区特殊的地形对这次特大暴雨过程有明显的增幅作用。

A mesoscale analysis and diagnose of an extreme bursting torrential rain in northwest of Yuanling on May 27, 2008 is performed by using the routine observational data, TBB data and NCEP reanalysis data. The results show that the heavy rainfall occurrs in the favorable environmental conditions,low-layer southwest jet brings moisture and instable energy for the heavy rain area. The MβCS convective system is formed by two mesoscale convective clusters , it shows an ellipse-shape structure and maintains over the heavy rain area for a long time. The heavy rainfall clusters appear in front of MβCS convective system where the convection development is strong. Mesoscale systems which are corresponding with the activity of rain clusters can be clearly seen from the stream field after filtering, and the heavy rainfall appears in the lower layer convergence between two mesoscale convergence lines of 850hPa and 700hPa . The rainfall relates to the distribution and change of the center of low-level positive vertical helicity and high level negative vertical helicity over heavy rain area. The existence of a secondary circulation forced by the ageostrophic wet Q-vector is propitious to the release of instable energy and plays important roles in the process of the heavy rainfall. The specific topography of heavy rain area results in precipitation enhancement.