| A large scale and continuous rainstorm occurred in South China on June18～23, 2005, which brought the serious flood disaster for the most provincesof South China. In order to understand the thermodynamic and motivecharacteristics, the structure of mesoscale system and the physics mechanismof this rain-storm process, this paper analyzed the systems of the processusing the measured data, the T213 numeric product and GMS TBB data andcarried on numeric simulation of the high time-space resolution making use ofthe MM5 no-hydrostatic numeric model. Based on the above result,diagnostic analysis was done, and initial conclusions were given out asfollows:(1) The trigger systems of this heavy rainfall process were high-level andlow-level jet and low vortex and shear line, and the direct reason of therainstorm continuation was born and eliminate of MCSs continuously in theconvective cloud system at the south side of low vortex;(2) The stable maintenance of the high-level and low-level jet wasimportant reason that the rainstorm process could keep on. The existence ofthe low-level jet played a decisive role for the water vapor transportation andmaintained the very beneficial vapor condition of the rainstorm area. Theample and stable water vapor mainly came from the Indian Ocean, which wasdifferent from the former rain-storm in south China such as "94.6" whosewater vapor mainly came from South China Sea;(3) It kept strong convection instability in the low level of convectionlayer above rainstorm zone, and kept symmetric instability in the middle andhigh level in the process. The coupling between high-level jest and low-level jet was a kind of motive mechanism that made this rainstorm occurs. Abovethe rainstorm zone, there was some obvious secondary circulations forced byfront-genesis, it might be the trigger mechanism of this rainstorm process.
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