冷空气对两例高原低涡移出高原影响的分析

Analysis for the Influence of Cold Air Mass on Two Cases of Plateau Vortex Moving Out of the Tibetan Plateau

利用NCEP再分析资料对2002年8月12～20日托勒涡及2003年7月12～14日诺木洪涡两例高原低涡在冷空气影响下移出高原的斜压性和温度平流进行诊断分析，结果表明：（1）受切变线影响的托勒低涡移出高原时主要受东北方冷空气不断伸入涡区的影响，西风槽前的诺木洪低涡主要受西北方冷空气伸入涡区的影响。（2）高原低涡是在600hPa以上涡柱内斜压性较强、500hPa涡区内斜压性加强情况下移出高原的。不同的是：托勒低涡移出高原，涡柱内对流层中上层斜压性、500hPa涡区内斜压性都比诺木洪低涡弱；托勒低涡涡柱内北冷南暖现象比诺木洪低涡强。（3）高原低涡是在低涡区内大部分受冷平流控制，涡区西部冷平流比东部强时移出高原的；低涡西部的冷平流加强将会使低涡发展加强，在高原以东持续。不同的是：受切变线影响的托勒低涡移出高原时低涡西部冷平流区强度比受西风槽前诺木洪低涡弱；而托勒低涡区冷平流区比诺木洪低涡移出高原时大。

Through the two cases of Plateau vortex moving out of the Plateau during 12-20 August 1998 and 12-14 July 2003, the baroclinic of vortex and temperature advection are studied. The results are as follows： （1） Tole Plateau vortex moved out of the Plateau mainly due to northeast lasting invasion of cold air flow and the Nomhon Plateau vortex moved out of the Plateau mainly due to northwest cold air invasion to the vortex area before the west wind trough. （2） Plateau vortex moves out of the Plateau when there is strong baroclinic condition above 600 hPa in vortex pole and also with strengthened baroclinic condition on 500 hPa in eddy area. But Tole Plateau vortex baroclinic condition in vortex pole and strength ened baroclinic condition on 500 hPa in eddy area are all weaker than the Nomhon Plateau vortex. Tole Plateau with north cold and south warm conditions is stronger than the Nomhon Plateau vortex. （3） Plateau vortex is mainly controlled by the cold air advection in the eddy area and moves out of the Plateau when the west cold air advection is stronger than the east the enhancement of the cold flux in west area will accelerate the development of the Plateau vortexes and will be good to the lasting time of the Plateau vortexes to the east of the Plateau. By influence of the shear line, the moving out of the Plateau Tole votex＇s west region strong cold air advection is weaker than the Nomhon vortex which is influenced by the west wind trough. And the cold air advection area of Tole vortex moving out of the Plateau is bigger than the Nomuhong vortex.