Abstract : 2G.2
The mean circulation field analysis of the Tibetan Plateau vortex moving out of the Plateau
Institute of Plateau Meteorology, China Meteorological Administration, Chengdu
By using the NCEP reanalysis data, the moving out of the Tibetan Plateau vortices activity characteristics in each month in summer from year 1998 to 2004 is analyzed. Furthermore, the comparison analysis of the monthly mean geopotential height, geopotential height difference distribution, temperature, wind field between the more vortex moving out of the Plateau June, July and August and less vortex moving out of the Plateau rule is gotten. The different characteristics between the Plateau vortex over the Plateau and the vortex moving out of the Plateau and the mean circulation field characteristics of the Plateau vortex moving out of the Plateau were acquired. All this had offered a scientific background for the prediction of the Plateau vortex which lead to the storm rainfall.
The main active time of the Tibetan Plateau vortex moving out of the Plateau is during May to August. This is different with the Plateau vortex active time over the Plateau, which is most often in May and less in August. Also this is different with the southwest vortex which moving out number is double in July than August.
The characteristics of more Plateau vortex moving out of the Plateau on 500hPa are: Bengal gulf trough is leaning to north or Subtropical High is extending west clearly, southwest air flow can influence the east area of the Tibetan Plateau; Southwest air flow and northwest can encounter or trough or shear line is active in east of Plateau and with cold air advection invasion.
The characteristics of more Plateau vortex moving out of the Plateau on 500hPa are: The South Asia High clearly extends to east and be stronger; The west wind is stronger; The east area of Plateau is controlled westnorth air flow before the South Asia High.
Key words: The Plateau vortex, moving out of the Plateau , mean circulation field.