The Study Of Tibetan MCSs And Synoptic-scale Wave In Southern China Using Satellite Data

Trajectories of Mesoscale Convective Systems (MCSs) over the Tibetan Plateau in summer during 1998 to 2001 are investigated by using Deep Convection Tracking products provided by the ISCCP DX Database and 2A25 vertical profiles of rainfall rate and TRMM 3B42_V6 global grid precipitation productions. The features of MCSs, such as trajectories, activity regions, origin distributions, life cycles, convective intensities, precipitation intensities and diurnal cycle are analyzed. The results show that there are two dominant directions for the MCSs while classified according to their move directions. One active forming region is over Yaluzangbu Valley while the other over the Mountain Hengduang, and the latter is stronger than the former. The average life cycle of MCSs is 37.39 h, and the average convective fraction is 22 percent over East China and Southeast Asia. MCSs develope dissymmetrically, the largest one's developing is the fast one. The peak time of MCSs forming is around 15 LST. Both the intensity of convection and the rate of precipitation increase at night, while both decrease at daylight. The diversities of cloud properties and precipitations are obvious between MCSs lie in the Plateau and plain. The diversities between two kind MCSs are different, it implies that there are more than one mechanisms effected MCSs' development, different environments have different mechanisms. In conclusion, while MCSs moving out of the Tibetan Plateau, their intensities are stronger, their precipitations are beaver.The relationship between Tibetan mobile MCSs and the summer rainfall over China is studied by using Deep Convection Tracking Database from ISCCP, reanalysis data from NCEP/NCAR, and precipitation data from 138 stations. Significant correlation is found between Tibetan mobile MCSs and the rainfall over China. The distribution of correlation coefficient presents to be four zonal bands, which is "—+—+" from south to north, just like the regular pattern of rainbands over China. The intensity of South Asia High, West Pacific Subtropical High and Northeast Cold Vortex are suggested to play their roles on the environment, thus affecting the birth of Tibetan mobile MCSs and rainfall over China.Based on the 6 years TRMM3B42 data for the period of i998-2003, the summer synoptic-scale wave in South China and in the Yangtze River basin are analyzed and compared. Results showed: the synoptic-scale wave in South China is westward, with a range of zonal wave-numbers k=1～9 and frequency f=-0.22～0.12. The range of frequency of the eastward synoptic-scale wave in the Yangtze River basin is f=0.20 to 0.29, with the same zonal wave-numbers as in South China. By the comparing analysis of the latitudinal, longitudinal and seasonal variability of synoptic-scale wave in South China and in the Yangtze River basin, this paper conclude that the summer synoptic-scale wave in South China is induced by the northward moving of the wave in Western Pacific tropical convergence, and the little plateau trough in westerlies is the main factor for the synoptic-scale wave in theYangtze River basin.