Mesoscale Structure of Torrential Rain Tropical Cyclone Over Liaodong Peninsula and the Effect of Complicated Topography

Using the NCAR nonhydrostatic mesoscale model MM5,the precipitation associated with typhoon Winnie( 9711) turning to Bohai Sea after landfall and topography forcing was simulated and its meso-scale structures was analyzed based on temperature of Block Body( TBB),disturbed streamline field and vertical velocity.The distributions of TBB display a clear mesoscale structure of convective cloud. The storm rainfall over Liaodong peninsula is closely related to mesoscale convec-tive system and topographic effect. The sensitivity experiments of topographic effect on the changes of precipitation and structure of typhoon Winnie show that:( 1) The local vertical circulations in north and east of Liaodong peninsula are favorable for formation and development of mesoscale convective cloud masses.( 2) Topography plays important roles in precipitation increment. The rainfall over the upwind slopes of the mountains and the precipitation cell intensity are increased with the topographic effect. Contrarily,the precipitation cell intensity is decreased without topographic effect. Heavy rainfall areas are corresponding to convergence zone.( 3) There exists significant increase of easterly wind velocity in the lower layer. Mesoscale cyclonic vortex systems are continuously generated and transported to the south of Liaodong peninsula which is favorable to sustain tropical cyclone( TC) intensity and induce heavy precipitation.( 4) The circulation of typhoon Winnie can be partly changed as the result of topography forcing. The local circulation of typhoon will be enhanced when cyclonic circulation initiated by topography forcing,and the rainfall will be increased accordingly,and vice versa.