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

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^-1 within 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.