A Study On The Mechanisms Of The Rainstorm In The Preflood Season In South China

The activity rules of southwest vortex, especially flood vortex influencing South China are, when moving paths in southeast and south-southeast appear in June, the southwest vortex causes the preflood season at increased risk. The typical affect systems of South China preflood are subtropical high, high and low level jet, etc. In order to select a typical South China preflood process, the 1°×1°NCEP reanalysis data from 13 to 14 June, 2009 was used. This article analyzed the synoptic situation and physics quantity field of the selected rainstorm process in South China by southwest vortex.Though synoptic meteorology analysis and physical field diagnosis, in the beneficial circulation background conditions, The primarily influence system in this process is southwest vortex, west Pacific subtropical high pressure and high and low level jet. Low pressure is actively in Northeast land nearby Bengal. The low level jet conveys water vapor, combined with energetic middle cold air activities, high-level nari field. The high-low configuration is a very good indicator to rainstorm. In this process, the troposphere middle-level cold air is strong in east of the Southwest China. The cold air flows south above the warm air. The instability enhances following strong rainfall.During rainfall, north Guangxi has the strong water vapor transmission and convergent, not only in the south for water vapor input, in its west most cases for water vapor input. From Bengal via indo-china peninsula of vapor transmission of water vapor main source, another part from Nanhai; Generally, rainfall ozone with vortex positive vorticity area is good, and the corresponding on the positive vorticity area of south airflow to occur during great rainfall. From heavy rains formed dynamic conditions look, south, north cold air level warm-moist air flow strengthening south emplacement, cold and warm airflow merger and produce cyclones circulation, be helpful for the development of the vortex strengthens. Boundary layer wind speed of convergence of Guangxi rainfall is very important. And from a thermal condition look, rainfall ozone heating is mainly caused by the latent heat of condensation. Non-adiabatic heating maintenance and development of vortex play an important role.