| Study has been made on a heavy rain system caused by Southwest Vortex happened in the eastern part of Sichuan and the western part of Chongqing on July 17,2007 by using tropical measure mission data combined the NCEP/NCAR FNL reanalysis data firstly. According to the orbit observations of TRMM satellite, the horizontal and vertical structure, the thickness of rain as well as the spectrum distributions of surface precipitation rate of this heavy rain system, and combined with the sounding data for further analysis of the vertical structure of precipitation, to explore the feasibility study of the precipitation structure of Southwest Vortex. Then comparative study has been made on the three dimensional structure, distribution of the rain top and precipitation profiles of two precipitation system caused by Southwest vortex which happened in Sichuan and Chongqing on 17 July,2007 and Tibetan Plateau Vortex which happened in the west part of Sichuan on 21 July,2008 respectively based on TRMM data, combined with the NCEP reanalysis data, summarizes the common feature and differences of two vortex systems and explain the reasons by using the dynamic theory. The following are the main conclusions that were obtained:(1)Analysis of the precipitation occurring on July 17,2007 caused by Southwest Vortex showed that:abundant moisture supply from Bay of Bengal and the combine of the high cold advection and low warm advection are an important factor affecting the precipitation. In horizontal structure,the heavy rain system was consisted of a main cloud and several scattered precipitation clouds, which was convective precipitation and characterized by high precipitation intensity and wide precipitation range. Although the number of convective rains is less than the stratiform rains detected by precipitation radar equipped by TRMM satellite, the former is the 7 times of the latter and convective rains contribute much more rainfall to the total than stratiform rains for the stronger rainfall rate of convective rams. The rainfall intensity spectral distributions of convective rains mainly occurred in 1-50 mm·h-1, the rain rate of almost 90% of the stratiform rains concentrated 10 mm·h-1 below and the rainfall intensity spectral distributions of stratiform rains mainly occurred in 0-20 mm · h-1.(2)In vertical structure of Southwest Vortex precipitation system occurring on July 17,2007:the rain top of heavy precipitation system can reach to 16km from the surface. The most precipitation rate occurred in the atmospheric 2-6km above the ground and the distributions of precipitation rate in both vertical and horizontal was inhomogeneous. The coalescence growth progress of cloud drop play an important role in the lower troposphere to precipitation. Whether stratiform and convective precipitation caused by Southwest Vortex, the precipitation under height of 6km contributed most, in different heights, the contribution of total precipitation was inversely proportional to the height.(3)Combined sounding data to study the vertical structure of heavy rain system of July 17,2007 can be concluded:Tropopause layer occurred in above the 100hPa pressure levels, which coincide the maximum rain top height in vertical section of strong rainfall centers researched by TRMM data. Moisture mainly concentrated in 7.5km below, which resemble with high value centers of precipitation rate obtained from vertical sections across of the main precipitation cloud captured by TRMM satellite located in2-7km. Above the 400hPa, False quite potential temperature θse is increased with the increase of the height, indicates the convection is stable, in other words,the height of convective cloud developed is relatively high.(4)Comparative analysis of three dimensional structure, distribution of the rain top and precipitation profiles of Southwest vortex and Tibetan Plateau vortex heavy rain system happened in Sichuan and Chongqing and on July 17,2007 and the west part of Sichuan on 21 July,2008 respectively find that.:the two precipitation processes were occurred in the southwest-northeast direction of the moisture convergence zone, clouds located in the southeast of Southwest Vortex. In horizontal, the two precipitations processes are all consisted of a main precipitation rain band and several scattered precipitation clouds, and the rainfall intensity and scope of Tibetan Plateau Vortex are much large than those of Southwest Vortex. The common feature of the two mesoscale precipitation systems detected by precipitation radar (PR) is that most of precipitation are stratiform precipitation which is characterized by large scope and weak intensity in precipitation, but the contribution of convective rains to the total rainfall is much large, the ratio and the contribution to the total rainfall of convective precipitation in Southwest Vortex is larger than it in Tibetan Plateau Vortex.(5)Similarities and differences of vertical structure between two precipitation system of low vortex are showed:the rain top of the two heavy precipitation systems is increased with the increase of surface precipitation rate, and the maximum rain top is close to 16km, but rain top of Southwest Vortex is higher Than Tibetan Plateau Vortex, which indicate that the convective than that of Tibetan Plateau Vortex. The progress of collision and growth of rain drop and the latent heat release were mainly occurred blow the height of 8km. But the change of precipitation of Southwest Vortex is greater than that of Tibetan Plateau Vortex, and the former is greater than the later for the contribution of rainfall at 8-12km height to total precipitation. |
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