Mesoscale Analysis of a Heavy Rainfall Event Along the Huaihe River Valley During 8-9 July 2007

During 8-9 July 2007, several successively developed rainstorms along the Meiyu front produced heavy rainfall in the Huaihe River Valley, which led to the most catastrophic flooding in this region since 1954.Through mesoscale analysis of both conventional and intensive observations from upper air and surface stations, automatic weather stations, Doppler radars, and the FY-2C satellite, the current study examines the developing style and environmental conditions of the mesoscale convective systems (MCSs) that led to the development of the rainstorms. Our analysis showed that this event went through three phases. The first phase of the heavy rainfall (Phase I) was caused by a meso-α-scale wind shear in the lower troposphere during 0200-1700 BT (Beijing Time) 8 July. Phase II was characterized by a reduction in rain rate and the formation of a low-level vortex between 1700 BT 8 and 0200 BT 9 July. In Phase III, the well-organized mature meso-α-scale low-level vortex brought about intensified rains during 0200-0800 BT 9 July. Satellite and radar observations showed a backward development of MCSs (new convective cells were generated at the back of the system) in Phase I, a forward development in Phase III, and a spiral organization of the convective lines in Phase II. The heavy rainstorm systems were initiated continuously along a surface mesoscale dew-point front with a horizontal scale of s300 km (as part of the Meiyu front) in the upper reaches of the Huaihe River Valley near Fuyang City, Anhui Province and then gradually decayed in the middle and lower reaches. It is hypothesized that lifting by strong low-level convergence is sufficient to trigger convection in the high CAPE (convective available potential energy) environment.