FORMATION AND EVOLUTION ANALYSIS OF THE MESOSCALE VORTEX GROUP IN THE MIDDLE AND LOWER REACHES DURING MEIYU OF THE YANGTZE RIVER

The Meiyu process in the middle and lower reaches of the Yangtze river on 22 June 1999 was analyzed in this paper using the dense observational data and the high-resolution out put of numerical simulation.The results show the heavy rainf all process was due to some meso-γ-scale disturbances formed in the mesoscale convergence line almost simult aneously in the boundary layer.Such meso-γ-scale vortex was located in the boundary layer initially,and the duration is a fewhours.The clarity of the cyclonic circulation is also different in the boundary layer,the cyclonic circulation of the disturbance in this paper is mostclear at 0.91 sigma level.