Abstract: Based on the NCEP/NCAR reanalysis data with the resolution of 1°×1° and the observational precipitation as well as the 3 h interval TRMM precipitation data, a heavy rain process on July 22, 2010 in the south of the middle of the?Yellow River was analyzed using a mesoscale Weather Research and Forecasting model (WRF). The results indicate that this rainstorm is simulated successfully by the WRF model. This rainstorm is generated together by a subtropical high over the West Pacific and a low trough in the Hetao area under a situation of large scale circulation. The abundant water vapor source is from the Indian Ocean and the Southern China Sea. The?mesoscale gravity wave is excited by the upper level jet stream on 200 hPa. According to the divergence field and cloud water distribution, the existence and moving direction of the mesoscale gravity wave could be determined. The reasons that effect of gravity wave on rainstorm generation in the east area of Gansu province are analyzed based on the simulation data. It shows that the mesoscale gravity wave in upper level jet and its absorption in lower atmosphere cause the formation of the rainstorm. According to the wind direction in upper jet and values distributions of the?nonlinear balance?equation (NBE), the area and moving direction of the mesoscale gravity wave could be determined in advance, so the falling area and time of rainstorm could be forecasted.

Key words: Tropical rainfall measuring mission (TRMM), Rainstorm, Numerical simulation, Gravity wave