短时强降水的多尺度分析及临近预警

利用安徽省1995—2010年逐小时降水量资料,统计了不同强度的短时强降水的时空分布特征,并分析典型短时强降水过程的环境背景场特征,建立了短时强降水的三种概念模型,总结出有利于其发生的大尺度影响系统。通过分析物理量得知,短时强降水发生时大气水汽充沛、湿层深厚,厚的暖云层保证了云粒子在降水系统的下沉气流里较少的被蒸发,而中等强度的对流有效位能和高的KI指数值有利于高降水效率的产生。短时强降水的雷达反射率因子有"低质心结构"和"高质心结构"两种结构特征。而径向速度场上的中小尺度风速切变、辐合、气旋式辐合则是强降水回波在某地维持和发展的重要原因。强降水发生前半小时边界层急流显著增强,也是短时强降水临近预警的一个重要指标。

Multi Scale Analysis and Nowcasting of Short Time Heavy Rainfall

Hourly precipitation data at 79 stations in Anhui Province during 1995 to 2009 were used to statistically compute the spatial and temporal distributions of short-time heavy rainfall with different intensity. Then the environmental background characteristics of typical short-time heavy rainfall were obtained so as to build three conceptual models of short-time heavy rainfall and abstract large-scale systems beneficial to its occurrence.By using the statistical analysis of physical parameters,conclusions can be drawn as follows. When short-time heavy rainfall occurs,the atmospheric water vapor is abundant and there are wetthick layer and warm-thick cloud layer,the latter ensures cloud particles from being evapored in the downdraft airflow of system.At the same time,moderate convective CAPE and higher KI index are beneficial for the appearance of high-efficiency precipitation.On the other hand,there are two structural characters of radar reflectivity factor,i.e.,the low-quality core structure and high-quality core structure.The important reasons for maintenance and development of heavy precipitation echo in some areas are attributed to small and mesoscale wind shear,convergence and cyclonic covergence zone.In addition,the boundary layer jet enhanced significantly half an hour before heavy rainfall is another important indicator of nowcasting of heavy rainfall.