Abstract: The circulation situation,mesoscale characteristics and cloud physics mechanism of precipitation during a short-time rainstorm process in Liaoning province from 20 to 21 July 2014 were studied based on NCEP (National Centers for Environmental Prediction) reanalysis data and high-resolution data output from mesoscale numerical WRF (Weather Research Forcast) model.The results show that the occurrence of the short-time rainstorm is firstly due to the fact that it is in front of the trough at 500 hPa and the shear line at 850 hPa and in the convergence zone of the left-hand side of the low-level jet.At the same time,the pumping action of upper-level jet strengthens ascending movement and a remote tropical cyclone transfers indirectly water vapor to Liaoning area along the west edge of the Pacific Subtropical High.Then,the β-scale cyclone on the ground triggers the precipitation at the storm center.In addition,the intrusion of the cold air has an important effect on the precipitation intensity.The maximum precipitation is collectively caused by the low-level convergence of the southward cold outflows from the sinking movement and southerly warm and humid inflows,and the middle-level convergence of northward and southward inflows.Besides,the γ-scale secondary circulation strengthens the ascending motion.Moreover,the cloud physical mechanisms of precipitation are different between the different periods.More specifically,when the heaviest precipitation occurs,the rainwater content increases rapidly with the growth of graupel particles,and cold cloud precipitation with the melting graupel particles plays a leading role in this rain.The efficiency of cold cloud precipitation is obviously higher than that of warm cloud,which causes easily the short-time heavy rainfall.

Key words: Short-time rainstorm, Numerical simulation, Pumping action, Mesoscale characteristics