Numerical experiments of the impact of Qin-Ba mountainous terrain on a rainstorm caused by southwest vortex

By using the CFSv2 reanalysis data and mesoscale model WRF V3.7.1,numerical experiments of a rainstorm caused by southwest vortex have been conducted.The study focuses on the impact of Qin-Ba mountainous terrain on the rainstorm.The results show that the topography is not conducive to the vortex moving to northeast by the blocking effects on vortex and on northerly and southerly flows along both sides of the mountain.Under the influence of the moisture transfer and vertical motion,the topography has changed the intensity and distribution of the rainfall.With the increasing of terrain height,rainfall begins to increase and rain belts move westward.The blocking effects of the topography make the moisture gather in the Sichuan basin,forming the strong convergence of the moisture flux on windward slope.The location and intensity of rain belts are consistent with the convergence region of moisture flux.Vertical motion forced by the topography is relatively strong on windward slope.Topographic uplift plays a dominant role while the frication convergence of a boundary layer also takes a considerable proportion.The heavy rain belt lies to the south of the ascending motion center,leading the formation of a local vertical circulation between the wake descending motion center which is outside the rainstorm region and the strong ascending motion center which lies to the north of the rainstorm region on windward slope.Thus the circulation can influence the interaction between vortex and shear line and the evolution of the rainstorm process.