The Research On The Effects Of Complex Terrain And Heavy Rains In Southwest Vortex

Using WRF mesoscale numerical model, the southwest vortex rainstorm in Sichuan basin happened on July 2-4,2012 is simulated with high resolution numerical experiment based on the WRF-3DVAR assimilation of southwest vortex encrypted data. On the basis of simulation results, southwest vortex structure features in different period of development are analyzed; Then conduct five sensitivity experiments including control test for the two cases of southwest vortex process happened on July 2-4,2012 and July 14-18,2010 to study the topography and thermal affections; Finally conduct control tests and 3 groups of topographic sensitivity experiments for a of southwest vortex rainstorm process in the Sichuan basin happened on 16-18 July 2010 using non-static equilibrium model(WRF) to study the dynamic affections of the complex terrain in the Sichuan basin in the southwest vortex generation, development and mobile period. The main conclusion obtained in this paper summarized as follows:(1) The encryption observation data of southwest vortex simulated by WRF-3DVAR can improved the simulation results; Numerical model WRF mesoscale non-static has good ability to simulate the process of southwest vortex.(2) The southwest vortex is shallow vortex circulation system in its primary period. It is divergence in low-layer and divergence in the high-layer. If the divergence in the high-layer is greater than the convergence in low-later, the southwest vortex will develop rapidly. It has a warm heart structure, because vortex controlled by high-energy moist air in low-layer. The southwest vortex will developed to deep closed low pressure circulation system in its mature stage, high-level divergence intensity is greater than the low-level convergence intensity. Because of cold air invasion in high-layer, cooling significantly in the low and middle layer, the low vortex developed from the warm heart structure to the baroclinic system. In die periods of southwest vortex, low vortex center divergence field configured for high-level convergence over the lower divergence. Because the cold air intrusion caused widespread cooling, low vortex changed to a baroclinic system, warm heart structure disappeared.(3) Don’t consider of latent heat flux and the surface latent heat flux, the deflection is obvious between simulation and the live of surface precipitation. Ground latent heating effect is not a decisive influence on the formation of a southwest vortex, but an important role in maintain the structure evolution, Were it not for the ground of latent heat flux, low vortex intensity is decreased, maintain time will be shorter, and the vorticity over the center of the low vortex, divergence and vertical velocity were altered obviously. The ground thermal plays an important role in the formation of the southwest vortex, not considering the ground thermal, low vortex intensity is weakened; After double the surface sensible heat, southwest vortex developed sharply, low-level convergence and high-level divergence configuration is changeless, low vortex vorticity center enhanced significantly.(4) And the results of sensitivity experiments show that the impact of Tsinling and Ta-pa Mountains on southwest vortex formation is insignificant, but it seems very important when it comes to the maintenance and development of the southwest vortex; and Transverse Mountain Range and Yunnan-Kweichow Plateau would mean a lot to the generation position, intensity and path of southwest vortex. Flow around plateau would form when easterly stream was blocked by the Tibetan Plateau and would have a positive impact on the generation of southwest vortex. What’s more this kind of flow would play an important role in moving of southwest vortex. Except of the southwest vortex, some small local vortices occurred in or around Sichuan Basin are deserved to be noted.