Abstract:By using 1°×1° NCEP/NCAR daily reanalysis data and conventional meteorological observation data, the Isentropic Potential Vorticity (IPV) theory was adopted to analyze the heavy rainstorm event during 24-25 September, 2009 in Huaihe River Valley. Results show that the mesoscale low vortex system of the lower troposphere in Huaihe River Valley had a close relation with the occurrence and development of this heavy rainstorm. The movement and intensity variation of high value center of 315 K IPV revealed the development of the mesoscale low vortex system, whose moving direction was consistent with the rain band's. The precipitation area was mainly located in the right side of high value center axis of IPV, where the strong Southwest jet appeared. Simultaneously, the dry cold air corresponding to the 345 K isentropic surface moved to the front of warm wet area. In the active period of development of the rainstorm, an obvious positive isentropic vorticity advection existed from the upper to the lower level of troposphere over the rainstorm area in Huaihe River Valley. The invasion of dry cold air led to the development of low vortex, the enhancement of convergence ascending motion and the increasing of heavy rain, which may be the significant triggering mechanisms for the heavy rainstorm.