Numerical Simulation Of Deep Convective Precipitation In The Eastern Tibet Flateau And Sichuan Basin

Based on the conventional observation data, satellite products and precipitation fusion products, using the mesoscale numerical model (WRF v3.4), a heavy precipitation occurred in the eastern part of the plateau in 2010 and two strong Precipitation process occurred in the Sichuan Basin caused by the plateau convection eastward movement in 2015 and 2016 are comprehensive analyzed and numerical simulated. From the macroscopic weather conditions, the circulation situation and the condition of strong convection, the micro-physical structure and the microphysical transformation of the micro-cloud, the macro-micro evolution characteristics of the two strong convective precipitation are analyzed. At the same time, the microcosmic evolution characteristics and precipitation formation mechanism of the strong convective precipitation cloud in the Sichuan Basin under the influence of the plateau vortex are compared and analyzed. The results show:The three heavy rainfall processes are similar in the weather conditions,both in the favorable weather of the subtropical high pressure northward lifting, cold air with the high latitude short slot transiting, low-level shear line convergence, and the southwest airflow bringing a lot of water vapor. However,the development of the subtropical high in the eastern part of the plateau in Case 15 is more intense than in Case 16. The water vapor in Case 15 is more abundant and the water vapor is more convergent and the precipitation is more.The plateau vortex was gradually weakened in Case 15,and there was a non-connected positive vorticity center in the Sichuan Basin. When the weak plateau vortex was moved to the Sichuan Basin at 8km, make up the middle level of the positive vorticity of the blank, so that the low level positive vorticity center of the Sichuan Basin is connected to the high level positive vorticity center, So that the vertical air flow becomes stronger and cloud development,resulting in heavy rainfall. In the Case 16, the plateau vortex was thick and the intensity was large, and the process of eastward migration was not weakened. In the Sichuan Basin, the high level and low level positive vorticity is weak, and when the strong plateau vortex is moved to the Sichuan Basin, the high level brings ice crystals, and the middle layer brings rich snow crystal. In the favorable weather situation, the low-level vorticity of the Sichuan Basin is strengthened, connected the high-level eastward shift of the plateau vortex, micro-physical transformation of the release of latent heat in the cloud, vertical air to further strengthen the cloud of continuous development, and ultimately produce heavy rainfall.Because of more abundant water vapor in Case 15 than Case 16, there was more cloud water at low level,super-cooled cloud water and ice phase particles existed at higher level, the maximum of the water content of ice in Case 15 was bigger than Case 16. During of plateau vortex moving eastward in Case 16, the convective clouds associated with the plateau vortex transported snow to Sichuan Basin, and the maximum of snow was bigger than Case 15. Snow in Sichuan Basin convection clouds of Case 16 was more abundant,the process of snow conversing to graupel was more active, graupel was more abundant than Case 15.During the precipitation process in the eastern plateau and the Sichuan Basin,the main sources of rainwater are graupel melting and the collection of cloud water by rain water at the first beginning. Graupel mainly comes from the collection of cloud water and rain water by graupel, because plateau vortex moving eastward takes a lot of snow, the conversion from snow to graupel makes an important contribution to graupel sources. Ice comes from cloud water freezing and condensation, but due to less super-cooled cold cloud, cloud water freezing to ice is weaker than condensation, and cloud water freezing to ice is similar with condensation in Case 15.