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

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 strengthened 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.