移出与未移出高原的高原切变线背景环流对比分析

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

利用NCEP再分析资料,采用对比分析方法,对2000-2004年汛期(5～9月)青藏高原(下称高原)上高原切变线活动过程进行了普查和分类,并对移出与未移出高原的高原切变线的生成日,移出高原的高原切变线的移出日与未移出高原的高原切变线的强盛日的背景环流特征场进行了对比分析。结果表明,500hPa层上,两槽一脊的背景环流形势有利于高原切变线的生成。较深的32°～49°N东亚大槽有利于切变线移出高原主体。移出高原切变线背景环流中的西太平洋副热带高压要比未移出的西伸明显。在对流层200hPa层上,南亚高压的存在有利于高原切变线的生成,移出高原的高原切变线上空的南亚高压强度要比未移出的强,而且相对较强的高空急流有利于高原切变线的东移。暖平流对高原切变线的生成有很重要作用,较强的暖平流有利于高原切变线移出高原主体;高原北部存在的较大正涡度平流有利于高原切变线的移出。移出高原主体的高原切变线在高原北部500hPa层上的正涡度平流要比未移出的强。

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.