In 2004 Chongqing "9.5" Heavy Rain And The Southwest Vortex Of Numerical Simulation

In this dissertation, a severe heavy rain process in east of SichuanBasin in Sep. 2004 was analyzed. Firstly, the environmental fields ofthe precipitation were diagnosed. Then, numerical experiment by MM5, anon-hydrostatic mesoscale model, was conducted to reproduce this process.Based on the mentioned-above successful simulation, we adopted the modeloutput data with high resolutions, to study the structure of SouthwestVortex in the mature stage. Finally, in order to study the role of "Sangda"typhoon, we also conducted the sensitivity experiment by filtrating thetyphoon.During the heavy rain process, the vapor come from the south-eastair current of South China Sea, and the air current reached Sichuan Basinby passing through the west of western Pacific subtropical high pressure(WPSH). After its formation, Southwest Vortex situated at the east ofSichuan Basin about 72 hours. The reason why Southwest Vortex situatedwas mainly the north-west moving of typhoon. When "Sangda" typhoon movedto north-west direction, WPSH was cut and the cut high pressure inmainland obstructed the east moving of Southwest Vortex. Meanwhile, thedeepen trough in the upper level(400～500hPa) maybe had positive roleto the development of Southwest Vortex.By using MM5 model, we simulated the synoptic process during 4～6Sep 2004. During 4～6 Sep 2004, Southwest Vortex(SW) was in its maturestage, so we analyzed the structure of SW by using the model output datawith high resolutions. The high pressure in east of SW blocked movingof SW. The study indicates that in the developing period of the low-levelSouthwest Vortex, there was a vortex in the middle-level all along,however, the center position of the middle-level vortex was on the southof the low-level vortex, and the development of the former was differentfrom the later. The development of the middle-level vortex was not"increase or decrease" simply, but the positive vorticity presentedincrease-decrease-increase again characteristic, the stage of the mostincreasing was different from the low-level vortex. It means that theupper vortex and the low vortex were not folded simply or coupledsynchronically.In the sensitivity experiment, we find that SW moved to east and northand the moving distance was about 3.5 degrees. The rainfall alsoevidently decreased, and the distribution of rainfall had changed. Thesensitivity experiment shows that "Sangda" typhoon had important roleto the stagnation of Southwest Vortex and the heavy rainfall.