Abstract:Radar echo characteristics of the vortex shaped mesoscale convective system (MCS) that produced heavy rain in Jianghan Plain of Hubei Province on 18 June 2011 and the possible causes of MCS structure are analyzed by using Doppler radar data, conventional observations and dense surface observations and the radar 4D Var wind retrieval data. The results show that: (1) Heavy rain producing vortex shaped MCS echoes in mature stage showed multiple spiral convective echo belts with cyclonic curvature, surrounded by stratiform cloud echoes and evolving into the cold and warm frontal structure as a result of invasion of cold air. Echo merger and vorticity train effect are the main characteristics of motion in producing severe precipitation. (2) The vortex shaped MCS which was in favorable environment was the result of severe development of boundary layer mesoscale vortex system in the transition zone of western Hubei mountain and Jianghan Plain. (3) The formation of the mesoscale vortex system was closely related to the development of the surface reverted warm trough, rainfall in the front of the southwest vortex and special terrain. Strong convergence of airflows from different directions was the main mechanism of the development in its earlier stage. The late development might be related to latent heat release, for the vortex circulation developed upward to 700 hPa.