Analysis On The Features Of Raindrop Size Distribution In Mei-yu Front During 2009-2010

Using the Parsivel laser precipitation Particle Spectrometer, four groups database of raindrop size distributions of heavy rainstorm on Meiyu front at Huainan and Nanjing were observed during summer,2009～2010. Gamma Rain Drop Size Distribution function is assumed and the parameters of the function are determined by moment method. Using Parsivel, radar and surface observation data, micro-structure of heavy rainstorm on Meiyu front were analyzed. The result shows that,(1) The precipitation of Meiyu front is merging cloud precipitation, there are many convective cloud, made up convective rain belt, in the large stratiform region. According to the evolution of raindrop size distribution of heavy rainstorm on Meiyu front, the heavy rain contribute to convective rain cells which was small size convective cloud and did not last long time, about 5 min to 30 min, in the Meiyu front. The rain cell had high concentrations of midsize drops, larger than 1000 m-3. Dm>2.0 mm.(2) According to analysis, there was evidence difference from characteristics of raindrop size distribution between main rain belt and the edge of rain belt, the precipitation of main rain belt had large concentration drops and the size of drops was big, but there was high concentrations of small drops at the edge of rain belt.(3) The raindrops which smaller than 1.0 mm contribute greatly to number concentration, but the raindrops of 1.0 mm-2.0 mm contribute greatly to rainfall rate of Meiyu front, and then the 0.0 mm-1.0 mm, next is 2.0 mm-3.0 mm, the raindrops of D>3.0 mm contribute smallest to rainfall rate of Meiyu front.(4) The raindrop size distribution of Meiyu front are mostly in double-modal character peaks without zero-modal,and then multi-modal,the least is single modal.(5) Diffrence from characteristics of raindrop size distribution, the raindrop size distribution peak diameter of Meiyu front increased with the increasing of rainfall rate, and then decrease. The parameters of Gamma distribution No,μ,λalways increase with rainfall rate. High concentration of larger raindrops contribute to large rainfall rate of Meiyu front.(6) The parameter, Nw and Dm,of raindrop size distribution of stratiform on Meiyu front distributed scattered with rainfall rate which indicate micro-structure of stratiform had characteristics of fluctuation. Except the data from Pukou in Nanjing on July 7,2009, the Nw and Dm of raindrop size distribution of convective cloud on Meiyu front distributed together, log10Nw and Dm was 3.5-4.5 and 1.5-2.3 mm respectively, indicated the characteristics of raindrop size distribution of convective have some similar. The distribution of Nw and Dm of convective were different from result of Bringi et al. (2003) which indicated there were difference characteristics from different precipitation.(7) The parameters of Gamma distributionμandλhad a good two-polynomial function, there is a great significance for calculation of modle and estimated precipitation in radar.(8) According database, we had Z-R relationship of heavy rainstorm on Meiyu front, Z=212R1.38, compared with the Z=300R1.40, the standard Z-R relation underestimated rainfall.