The Formation, Development And Spread Of The Mesoscale System During The Period Of MeiYu Storm Rainfall In 1991

By using MM5, we simulated the rainfall process during the period of 0000 GMT 5 Jul to 1200 GMT 6 Jul 1991 successfully. And the diagnostic analysis was carried out to study the relationship between high and low level jet and rainfall, the relationship between southwest vortex and rainfall, etc. It was found that these elements had a close relationship with the change of rainfall. They had the good homologous relationship with the rainfall.The center of southwest low jet currently lay in the southeast quadrant of southwest vortex. When the baroclinicity of southwest vortex had not been built and where cold front existed, the rain belt may lie in anywhere of the left of southwest low level jet. But when the baroclinicity of low level vortex was strengthened and when warm air came into being, all the rain belts lay in the left and the front of southeast low level jet. The trend of high level jet had great relation to the motion of southwest vortex. When the east of China lay in the region of northwest jet , the southwest vortex was stable because this influence benefited for maintaining the eastern ridge. When the east of China lay in the region of west jet, the ridge moved to the east and the southwest vortex moved to the east rapidly. And when the east of China lay in the region of southwest jet, the southwest vortex was strengthened and moved slowly.We analyzed the meso-scale disturbance field and found that the development and spread of inertia-gravity wave had a close relationship with the development and spread of the rain belt. At the initial stages of precipitation, convection instability was strong in the low level above rain region. Convection instability could inspire inertia-gravity wave. It was benefited for southern spread of inertia-gravity wave in the symmetric instability region of the south of the high layer of rain belt. The southern spread of low-layer inertia-gravity wave was benefited for coming into being of excessive strip rain belt. The appearance of southern spread of inertia-gravity wave in high layer was earlier than the one in low layer. The vorticity and divergence belt take on eight as time processes. The high-layer northeast-southwest vorticity and divergence belt spread towards the south and northwest-southeast vorticity and divergence belt spread towards the north. In the metaphase of precipitation, the high-layer inertia-gravity wave presented indirect circulation posture circling the center of low-layer vortex. .At this time precipitation became stronger and moved towards the east. The north of the low-layer of rain belt was mainly convection instability. So the northern inertia-gravity wave was not easyto develop and to spread. The northern spread of high-layer inertia-gravity wave could result in the development and northern moving of low-layer vortex and precipitation. So we found that convection instability could inspire inertia-gravity wave. Symmetry instability was benefited for spread of inertia-gravity wave and further influenced the development and motion of precipitation. The combining of symmetric and convection instability had great influence on precipitation.