Analysis and Numerical Simulation for Effects of Vortex and Jet Stream on Heavy Rain in East Sichuan in September 2004

We have analyzed the effects of vortex in the basin and jet stream on heavy rain in the east of Sichuan province in September 2004,and have done numerical simulation.The results show the process of precipitation is related to mesoscale cloud mass,jet stream and vortex activities in mid- and lower- levels,at the same time,and along with to activities of subtropicalhigh pressure and !SHANG DAtyphoon.The vortex in Sichuan basin appeared in the left of lower- jet stream,and the heavy rain in the east of Sichuan occurredin the south of upper level jet stream,there exits strong south-east lower jet stream to south-east of low vortex.Maintaining of positivevortex in the basin is benefitto the development and lasting of the vertical ascending movement over the basin,and provided dynamic condition for heavy rain.Vertical ascending movement was the ligament linking jet stream and basin vortex as well as dynamic driving result in the basin.Thesouth-west jet stream had built before the heavy rain appeared,and heavy rain and basin vortex appeared almost at the same time,as well as the heavy rain,low jet stream and basin vortex weaken together.The high jet stream was progressively increasingbefore and during the process of the precipitation.When the upper leveljet stream weakened,heavyrain was ending.