Analysis On Microphysical Characteristics Of Convective And Stratiform Cloud Precipitation In Beijing

Convective cloud precipitation and stratiform cloud precipitation are the most important precipitation in Beijing summer. From the macroscopic view, convective cloud precipitation has high precipitation intensity but persist no more than3hours with several km in width. Stratiform cloud precipitation persist1-2days with more than100km. Using1044raindrop samples which were obtained from2003to2008,in northwest of Beijing to contrastive analyze raindrop spectrum of convective cloud precipitation and stratiform cloud precipitation. Gamma raindrop size distribution function assumed and the parameters of the function are determined by moment method. Using radar and surface observation data, micro structure of Convective cloud precipitation and stratiform cloud precipitation were analyzed. The result shows that,(1)According to analysis, there was evidence difference from characteristics of raindrop size distribution between Convective cloud precipitation and stratiform cloud precipitation, Convective cloud precipitation had normal concentration drops and big size drops, but there was a high concentration of stratiform cloud precipitation with small size drops.(2)The raindrops which smaller than1.0mm contribute greatly to number concentration, but the raindrops of1.0mm-2.0mm contribute greatly to rainfall rate of Convective cloud precipitation and stratiform cloud precipitation, and then the0.0mm-1.0mm, next is2.0mm-3.0mm, the raindrops of D>3.0mm contribute smallest to rainfall rate of Convective cloud precipitation and stratiform cloud precipitation.(3)The raindrop size distribution of Convective cloud precipitation are mostly in double-modal character Peaks without zero-modal, and then multi-modal, the least is single modal. The raindrop size distribution of stratiform cloud precipitation are single modal mostly in without zero-modal, and then multi-modal, the least is double-modal character Peaks. (4)Both the rising of the size and the concentration of the raindrop can enhance the precipitation in the convective or stratiform cloud precipitation of Beijing. It is well-founded in observation that increasing the condensation nucleus can enhance precipitation through seeding hydroscopic nucleus into the cloud.(5) Differences from characteristics of raindrop size distribution, the raindrop size distribution Peak diameter of Convective cloud precipitation and stratiform cloud precipitation increased with the increasing of rainfall rate and then decrease. The parameters of Gamma distribution No,μ,λ always increase with rainfall rate. High concentrations of larger raindrops contribute to large rainfall rate of convective cloud precipitation and stratiform cloud precipitation. The parameters of Gamma distribution μ and λ had a good two-Polynomial function; there is a great significance for calculation of model and estimated precipitation in radar.(6) According database, we had Z-R relationship of convective cloud precipitation and stratiform cloud precipitation, Z=223R1.56, Z=115R1.07compared with theZ=300R1.40the standard Z-R relation under estimated rainfall.