Abstract:Based on the conventional observation data, Doppler radar data and NCEP (1°×1°) reanalysis data, the causes for weakened typhoon generated heavy rainfall on 8 August, 2008 (called “0808” process for short) and Meiyu period heavy rainfall on 4 July, 2003 (called “0307” process for short) in Chuzhou, Anhui Province are diagnosed and analyzed. The diagnostic results show that the enhancing of low level jet can prompt heavy rainfall, especially heavy rainfall happening during night. In these two heavy rainfall events there exist secondary circulations, but the modes of their action are different, they both enhance high and low level weather systems. A great amount of water vapor from the weakened typhoon plays an important role in the “0808” process, and a strong water vapor transport is not necessary for producing heavy precipitation. Meanwhile the strong water vapor convergence center of heavy rainfall is located in the boundary layer, and cold air is important for heavy rainfall. During the “0307” process, radar precipitation echoes stay for long time. And the main feature of “0808” process in Doppler radar is that severe storms lead to convective precipitation.