Classification And Radar Echo Features Of Rainstorms In Flood Season In Hunan

Rainstorm is one of the most disastrous weather. Long duration, heavy intensity of rainstorm can often cause flooding, which can bring to people’s lives and property and socio-economic harm. To study and forecast of rainstorms is of great significance.Hunan is one of the identities of the rainstorm in China. Based on hourly precipitation data of the97weather stations in Hunan province from May to July in2007-2010, radar data which were got once every6minutes from Changsha radar station and high resolution of FNL (Final Analyses) data which were got from United States national environmental forecast Center (National Centers for Environmental Prediction), to analyze the characteristic analysis of rainstorm in flood season (May-July) in Hunan.The temporal and spatial features of rainstorms were analyzed in the flood season in Hunan. The high occurrence period of rainstorms is from05o’clock to09o’clock and the main peak is at08o’clock. Northwest and southeast of Hunan province, Loudi, Yiyang, Changsha and Yueyang are the strong precipitation areas.The total numbers of rainstorms from May to July in2007-2010and all kinds of rainstorms based on the classification of torrential weather situation were satisfied. There were87rainstorms and719points. 27southwest jets rainstorms were found;9Vortex rainstorms were found;20shear rainstorms were found;6the long distance interaction of Typhoon rainstorm were found.The characteristics of Doppler weather radar of rainstorms in flood season were summarized in Hunan. Jet rainstorm echoes are block or wool which often generate in Western Hunan and moves to the Northeast. The average strength of strong echo Center is49dBZ and its ET is flat; Speed characteristics are presented as a significant southwest, and adverse wind areas can analyze in radial velocity. Vortex rainstorm echoes generate mainly outside of Hunan which move to East. The average strength of strong echo Center is45dBZ and its ET is about to the thickness of Vortex; Speed characteristics are presented as a clear convergence in radial velocity. Shear rainstorm echoes are E-W or NE-SW trend band which generate mainly outside of Hunan.The strength of strong echo Center of warm type shear rainstorms is lower and ET is flatter than cold type shear rainstorm. Speed characteristics of warm type shear rainstorms echoes are presented as veering with height, where in other words exist warm flat flow, and there are gale nuclear on2.4°and4.3°elevation. Speed characteristics of cold type shear rainstorms echoes are presented as backing with height, where in other words exist cold flat flow, and zero speed line appears90°folding angle. Distribution of the long distance interaction of Typhoon rainstorm echo is comma-shaped single. Every single echo is clear, and there aren’t large tracts of low intensity echoes around strong echo center. Echo overall move to West; Positive and negative speed convergence are shown on radial velocity, which indicates convective activity.Three rainstorms were analyzed."100506" and "100513" rainstorms of central Hunan region were analyzed comparatively. It is shown that the characteristics of "100506" rainstorms echo meet the warm type shear rainstorms echoes, and the characteristics of "100513" rainstorms meet Jet rainstorms echoes. The analysis of "100619" rainstorms in Hunan is shown that its echo meet Jet rainstorms echoes and Vortex rainstorms echoes. Echoes are mixed precipitation echoes to Cumuliform cloud mainly, and strong echo to do big contribution to precipitation. SW Jets are shown on radial velocity. Adverse wind areas and heavy rain areas matched very well. Junior convergence and senior divergence provide favorable conditions to maintain widespread precipitation.