Abstract: In order to understand the triggering and developing mechanism of Mesoscale Convective System (MCS) in the Tianshan Mountains,the causes of MCS in a short-time severe precipitation process under the background of Central Asian vortex in the Ili Valley of Xinjiang,China were analyzed deeply.Based on the hourly precipitation data,the temporal spatial distribution characteristics of the precipitation were obtained.The cloud pattern and radar characteristics of MCS were analyzed according to FY-2G satellite TBB products and Doppler weather radar data.The results indicated that M_βCS in this area had obvious characteristics of nocturnal and backward propagation,being formed over the mountain areas and developed,enhanced and retained for a long time period over the plain areas.The continuous occurrence of strong echo zone,adverse wind region and ultralow level jet on the radar map illustrated the enhancement of local convection.Moreover,the rainfall intensity of representative stations was analyzed with corresponding TBB and radar echo,which showed that the spatial and temporal distribution of rainfall intensity was proportional to the TBB gradient,ET and VIL respectively.Using sounding,surface wind field and ERA-Interim reanalysis data,the largescale circulation background and mesoscale characteristics of MCS was analyzed,which concluded that enhanced local convective activity triggered the formation of MCS in the front of deep Central Asian vortex,and the multi-channel water vapor transport and long-time water vapor convergence in the middle and low levels,the atmospheric instability stratification,and convergence and vertical shear of wind field in the low and middle levels,the increase of θ_se between the upper and lower level and the enhancement of warm advection in the lower level provided better dynamic,thermal conditions and water vapor for the development and retainment of MCS.

Key words: CentralAsia vortex, MCS, shorttime severe precipitation