Abstract:Using conventional meteorological data, regional automatic station precipitation data, NCEP 1°×1° reanalysis data and FY 2E satellite cloud image, evolution characteristics of the circulation situation, causes of the rainstorm and mesoscale features of the continual torrential rain process in Jilin Province from 14 to 17 in August 2013 were analyzed. The results show that in the unusually stable large scale circulation background, the torrential rain was mainly caused by two upper troughs which moved to the east along the same path on the middle latitude frontal zone and repeated impacting Jilin Province.The precipitation process was divided into two major stages. In the first stage, it was severe convective precipitation. θse frontal zone tilted to the south along height unstably and water vapor was abundant, forming large convective available potential energy. In the second stage, however, the rainfall gradually turned to mixed severe precipitation. θse frontal zone tilted to the north with height, the intensity of water vapor transport, precipitation duration and total rainfall amount were significantly stronger than in the first stage. During heavy rainfall, α mesoscale convective cloud cluster or MCC was formed successively and divided into 3 stages, impacting Jilin. In the developing stage of cloud cluster, there was a vertical structure of cyclonic vorticity with the mesoscale convergence on low altitude, anticyclone vorticity with the mesoscale divergence on high altitude, and the rising velocity was obvious. At the same time, the recurring of the wind speed convergence which was in the front of a ultra low level jet at 925 hPa was also the possible mesoscale triggering mechanism of the continual heavy rain.