Characteristics Of A Severe Rainstorm On June23,2011in Beijing And Impacts Of Cloud Microphysical Processes

By using data from FNL, Automatic Weather Station, FY-2E satellite, Doppler radar and regular observations, the characteristics of a severe rainstorm on23June2011in Beijing is investigated. The effect of ten cloud microphysics schemes on the location, intensity and starting time of rainfall for the severe rainstorm and the possible reasons leading to precipitation differences are studied using the Weather Research and Forecasting Model (WRFV3.2.1version) with model resolution of6km and2km respectively. Based on the sensitivity experiments of the different microphysics schemes, Lin’s scheme is chosen to study the cloud microphysics structure against with observational data.The results show that the blocking high near Lake Baikal, the upper trough and the subtropical high are the influential large scale systems, the main influence system in middle and lower troposphere is a vortex. The ascending air current in Beijing generated by convergence in the lower troposphere and divergence in the higher troposphere before the heavy rainfall is a favorable dynamical condition for the occurrence of heavy rainfall; vapor transport by vortex and convergence of vapor in Beijing provides abundant vapor for generation and maintenance of the heavy rainfall; the CAPE accumulated and unstable stratification above the rainfall region create favorable energy and stratification conditions. The analysis of radar data indicates that the strong development of meso-β-scale and meso-y-scale convective systems is the main triggering reason for the heavy rainfall.Different cloud microphysics schemes are very sensitive to rainfall location, intensity and starting time. With different cloud microphysics schemes, the very large differences of rainfall amount and location can be found for18h accumulated rainfall. Most cloud microphysics schemes simulate very larger area of the heavy rainfall, but weaker intensity of heavy rainfall center, and the heavy rainfall tends to distribute on the north comparing with that observed. Lin schemes are closer to observed ones in heavy rain location and distribution relatively. The increase of model resolution, for some cloud microphysics scheme, conducive to forecast heavy rainfall intensity but has very little impacts on the scope and distribution of heavy rainfall. The simulated starting times of maximum rainfall intensity by Lin scheme, Thompson scheme and WSM6scheme are closer to that observed, but other schemes have different time delay. Most cloud microphysics schemes have1-2hour advance in starting time. The simulated differences of vertical velocity, hydrometeor mixing ratios and atmospheric humidity profile caused by the differences of conversion process from vapor to hydrometeors in ten cloud microphysics schemes lead to the differences in simulated precipitation.The vertical integrated mixing ratio of cloud, rain, and graupel are higher and those of ice crystal and snow are relatively lower. In different stages of cloud development, vertical integrated mixing ratios are significantly different. Hydrometeors at different locations have different distributions and amounts. Generally, the cloud water and rain water are mainly distributed in the middle and low troposphere, but there are sufficient supercooled cloud water and rain water when the convection is strong.Graupel is mainly distributed in middle and upper troposphere and the mixing ratio is higher than other hydrometeors. Ice crystal and snow are mainly distributed in upper troposphere and the mixing ratio are smaller. Graupel and rainfall in the ground have a similar variation tendency, which shows that the melting of graupel is important to the rainfall on the ground.