Contrast Analysis on Background Circulation of Plateau Shear Line Moving Out and not Moving Out of the Tibetan Plateau

Using the NCEP reanalysis data,based on the contrast analysis of the background circulation impacting on plateau shear line moving out and not moving out of the Tibetan Plateau in summer from 2000 to 2004 are analyzed.The result indicates that,the situation of 'two troughs and one ridge' is stable in middle and high latitudes on 500 hPa,which helps the the genesis of plateau shear line.The meridional circulations with the East Asian Trough along 32°~49°N are beneficial to plateau shear line moving out the Plateau.And East Asian Trough and the west westward extension of Pacific Subtropical High are significantly in the circulation background of plateau shear line moving out of Tibetan Plateau comparing with plateau shear line not moving out of the Tibetan Plateau.On 200 hPa troposphere layer,the existence of South Asian High is beneficial to the generation of plateau shear line,and South Asian High of plateau shear line moving out the Tibetan Plateau is stronger than that not moving out of it.And stronger of the upper jet stream is beneficial to plateau shear line to move eastward.In the middle troposphere the warm advection is very important to generation of the plateau shear line.On the Tibetan Plateau,positive vorticity advection in the middle troposphere is very important to generation of the Plateau shear line.Positive vorticity advection of plateau shear line moving out of the plateau is stronger comparing with plateau shear line not moving out of the Tibetan Plateau.