郑州市两次短时强降水过程的环境条件和中尺度特征对比

Comparative analysis on environmental conditions and mesoscale features of two short-time heavy rainfall events in Zhengzhou

为了探求不同天气影响系统和垂直风切变下中小尺度系统造成的城市短时强降水过程的预报预警特征,以2007年8月2日和2008年7月11日发生在郑州市的两次短时强降水过程为例,利用常规观测资料以及河南省区域自动站、雷达探测资料等,对其大尺度环境条件和中尺度特征进行了对比分析。结果表明：以露点锋为触发机制的强降水超级单体和以锋区造成边界层辐合线为触发机制的混合性降水回波,虽然其雷达回波表现形式不同,但在地面中小尺度系统的作用下,都产生了1~2 h雨量达100 mm·h-1左右的短时强降水;地面辐合中心和高温高湿中心为短时强降水提供了动力抬升、热力不稳定能量和水汽条件;不同的0—6 km和0—2 km高度垂直风切变导致不同的对流回波形式,产生相同强度的短时强降水;短时强降水的降水效率不仅与云中降水粒子的大小有关,还与其数密度有关,即降水强度既与降水回波强度有关,也与其降水云中的滴谱分布有关;两次短时强降水过程分属于强对流型和热带降水型。结合地面加密站观测资料中小尺度分析与雷达探测产品分析,可对此类短时强降水发生提前预警。

The objective of this study is to explore the forecasting and warning characteristics of short-time heavy rainfall events in urban area which are caused by meso- and micro-scale synoptic systems under different circulation patterns and vertical wind shears. Taking two events occurred in Zhengzhou, Henan province on 2 August 2007 and 11 July 2008 as examples, the authors comparatively analyzed the large-scale environmental conditions and mesoscale features of the two events by using conventional meteorological observations, intensive automatic weather station observations and Doppler weather radar data in Henan. The results indicate that both the heavy rainfall supercell triggered by dew point front and the mixed precipitation echoes triggered by boundary layer convergence line in frontal zone generate short-time heavy rainfall of 100 mm·h-1within 1-2 h under the effect of meso- and micro-scale synoptic systems in ground level, although their radar echoes showed differences. The ground convergence center and the high temperature and humidity center provide dynamical lifting, thermodynamic instability and water vapor conditions for the formation of short-time heavy rainfall. Short-time heavy rainfall with the same strength can be induced by different vertical wind shear of 0-6 km and 0-2 km height which lead to the difference in convective echoes.Precipitation efficiency of short-time heavy rainfall is not only related to the size of precipitation particles in the cloud but also to their number density. Namely, the precipitation intensity is not only related to the precipitation echo intensity but also to the distribution of droplet spectrum in the precipitation cloud. The two short-time heavy rainfall events belong to the strong convection type and the tropical precipitation type, respectively. Two types of short-time heavy rainfall can be early warned on the basis of meso- and micro-scale analysis of observations from intensive automatic weather station and radar observations.