Dynamic Analysis Study On Southwest-vortex Can Increases The South China Rainstorm

This paper use the global reanalysis data of NCEP analyzed the synoptic situation and physics quantity field of a rainstorm process in South China from 13 to 14 June, 2006. Through the diagnosis and analysis, the affections of several weather systems on different scales in the rainstorm process have been illustrated completely. Also use the theories of disturbance wave ensemble under nonzonal basic flow, the dynamical mechanism of the increasing to rainstorm caused by the Southwest-vortex was discussed from meso-scale energy aspect. The main results are yielded as follows:By 1980-1999, 4-9 months, the southwest low vortex affect the south China region rainstorm weather process Pronk investigation and statistics. It's show that:Southwest-vortex influences South China rainstorm mostly in May, June and July, when flood-causing storms appear most frequently during the year. The existence of Eurasian trough, the southward-moving of subtropical high and the ridge over east coast are the circulation background to form southwest- vortex. Simultaneously, large scale of warmer area in lower layer is favorable to the growth and strengthening of southwest-vortex.The subtropical high, trough and ridge moving along the westerlies to transport for water vapor, the cold and warm, jet etc. created the environment condition of large scale upper and low level jet are advantageous to vertical sport and circulation occurrence, also making the high low altitude momentum exchange, promoting the formation of whirlpool. Southwest-vortex and jet are the direct influence systems to rainstorm, there's close relationship among the happening of rainstorm, Southwest-vortex and the vapor flux in the Bengal Bay on the 850hpa, and the minus helicity on the 500 hpa was propitious to the development of low pressure in lower layer. Form these diagnostics, It was confirmed that these variety of physical quantity and the rainstorm process are fit together, various conditions all are advantageous to the occurrence and the development of rainstorm.Effects of nonzonal basic flow with the balance of gradient wind on meso disturbance wave ensemble are investigated. There's a cyclonic Southwest jet in the upper air of South china, under the condition of balance of gradient wind and the Southwest-vortex move to the South china, the gravity wave energy spreads toward the south, which caused the increasing of energy of inertia gravitational wave of South China. And the Southwest-vortex had the positive contribution to the rainstorm of South China, which means it has some increasing effect to the rainstorm.