Numerical Simulation Analysis Of Two Rainstrom Processes In The South Of Tibetan Plateau In Summer

This paper selects two rainstorm processes that occurred in the south of Tibet Plateau in summer,namely the rainstorm process of Linzhi on August 19,2015 and the rainstorm process of Shigatse to Lhasa area on July 7.The precipitation characteristics,large-scale circulation situation,and the development of mesoscale convective clouds are analyzed using various observations.The mesoscale numerical model WRF is used to simulate the two precipitation processes and analyze the structural characteristics of the mesoscale system.Finally,different cloud microphysical parameterization schemes are used for numerical simulation experiments.Therefore,the influence of the selection of microphysical schemes on the simulation effects of two precipitations is analyzed,and the characteristics of the microphysical processes of the two rainstorms are analyzed.The main conclusions are as follows:(1)The synoptic analysis shows that the two rainstorms are divergent at the upper troposphere 200 hPa under the influence of the South Asian high and highaltitude jets.There are transverse shear lines existed in 500 hPa,and the low-level convergence of the plateau vortex is beneficial.The characteristics analysis of mesoscale convective clouds shows that the main cause of the "8.19" rainstorm is the linear convective system with the convergence line,and the main impact system of the "7.7" rainstorm is the mass convection system.(2)The mesoscale numerical simulation and diagnostic analysis of the two rainstorm processes show that there are sufficient water vapor supply during the two rainstorms.The rainstorm zone existed low-level convergence,high-level divergence,and positive vorticity with strong upward motion.The vertical structural features,as well as the favorable atmospheric thermal structure,provide dynamic conditions and thermal conditions for the occurrence and development of the rainstorm process.The “8.19” process is affected by the terrain,and there is obvious subsided airflow,which is more conducive to the continuous development of rainstorm.The distribution of vertical helicity of the “8.19” rainstorm is more favorable to the system.This is also one of the reasons for the greater intensity of the "8.19" rainstorm.The vertical helicity positive value area are correspond to the falling area of strong precipitation.(3)The numerical simulation test was carried out on the two rainstorms of "8.19" and "7.7".In the process of two rainstorms,the distribution of rain bands simulated by different schemes is similar,the trend and area of simulated rain bands are close to the real situation,and the intensity of simulated precipitation is different to some extent.The results of the TS score showed that the scores of the four two-parameter schemes were higher than the other two single-parameter schemes.The overall scores of the Morrison and NSSL schemes in the “8.19” rainstorm were higher,and the overall score of the Morrison scheme in the “7.7” rainstorm was highest.(4)The distribution of solid water condensate in the cloud can correspond well with the falling area of precipitation,and the content of liquid water condensate is less.The maximum value of solid water condensate is mainly located at 300 hPa-400 hPa,which can extend to the top of troposphere.There are some differences in the distribution of water condensate simulated by different schemes.Lin scheme simulates few solid water condensates.The main solid water condensates are graupel particles,and there are more liquid water condensates than other schemes.The other five schemes resulted in the highest concentration of ice particles and the lowest concentration of snow particles,The analysis of the FMSE? of different schemes shows that the two-parameter scheme has less negative effects on the development of cumulus convection.