Comparison Analysis of Circulation Features of Different Moving Tracks of Long-Life-Cycle Plateau Vortexes Moving out of the Plateau
Using the upper-air observation data and the corresponding daily average NCEP reanalysis data, this paper first statistically analyzed the plateau vortexes which could live 3 days or longer after moving out of Tibetan Plateau in summer from 2000 to 2010. According to their different moving track, the vortexes were divided into three groups which are moving eastward, northeastward and southeastward. The results show that in July long-life-cycle vortexes moving out of the plateau move eastward far more than northeastward and southeastward, and the vortexes moving southeastward are more than those moving northeastward. However, in August, the vortexes moving southeastward are far more than those moving northeastward and eastward. Then by selecting the cases of different moving tracks, we analyzed the general circulation in the mid-upper troposphere, pointing out the common features and differences of the general circulation and temperature advection at 500 hPa and the circulation at 200 hPa. The findings indicate that the position and shape of West Pacific subtropical high influence the long-life-cycle plateau vortex moving out of the plateau at 500 hPa significantly, and the strength of the subtropical high decreases in the order of the tracks moving eastward, northeastward and southeastward. The southeastward track over the IndianBurma Region is affected by monsoon depression while the eastward and northeastward tracks are affected by the Indian monsoon trough, namely to south of 25°N of the southeastward track there is a relatively lower geopotential height which is favorable for the plateau vortex to move southward. Under the 200 hPa circulation background, the eastern end of the 1252 dagpm South Asia high is by west in the order of eastward, northeastward and southeastward tracks. For the eastward track cases, the eastern end of South Asia high is obviously by east, causing the westerly flow to guide the plateau vortex to move eastward. And for the southeastward track cases, the northern boundary of the South Asia high over the Tibetan Plateau and north-west flow after high trough at 110°E guide the plateau vortex to move southeastward. Cold air is also an important factor for the development of these long-life-cycle plateau vortexes. The corresponding relationship exists between the moving direction of the temperature advection zone and the moving tracks of long-life-cycle plateau vortexes moving out of the plateau.