Dynamics Study On The Relationship Between Plateau Shear Line And Plateau Vortex

Based on the atmospheric motion equations and the European Center(ECMWF)ERA-interim reanalysis data,this paper first use barotropic equations in the z coordinate system,and then analyze shear wave and vortex wave containing terrain slopes and without considering terrain slope and the relationship between them in theory,thus,the relationship between the shear line and the low vortex is obtained.Secondly,considering the water vapor conditions,using the atmospheric motion equations and divergence equation,this paper analyze and discuss the stability of the disturbance involved with the transverse shear line(TSL)over the Tibetan Plateau(TP)and the dynamical mechanism of the Tibetan Plateau vortex(TPV)induced by the TSL under the condition of vapor convergence then verify it.Finally,analyze the interaction mechanism between shear line and low vortex,then use the motion coordinate system,discuss the factors which affect the shear line,the low vortex meridional and zonal movement,the following conclusions are drawn:(1)The fluctuations caused by the zonal wind speed shear on both sides of the plateau shear line include shear wave,inertial wave and gravity external wave,which belong to the two-way scattered wave,the wave velocity is related to the basic airflow and the basic airflow shear,and is also related to the ground rotation parameters,the Newton sound velocity,the terrain slope,and the wave number k.The instability of the fluctuation on the shear line is related to the wave number,and the fluctuation of the small wave number is prone to unstable development,the contribution of terrain slope to stability fluctuation depends on the zonal distribution of the basic flow.Vortex wave instability is a special case of shear wave instability,and under certain conditions,the shear wave instability will induce the instability of the vortex wave.The unstable development of the disturbance on the plateau shear line can promote the occurrence and development of the plateau vortex,which is closely related.(2)The TSL is an important background field of TPV.The TPV induced by the transport of water vapor which located in the south of the TSL is associated with the adjustment of divergence field caused by the unbalanced of atmosphere,which is favorable for the formation of TPV in the position where the convergence is enhanced,the center of the TPV corresponds to the positive center of unbalanced items and the periphery of the TPV is negative area of unbalanced items.When the southwest wind increased and move toward the east or northeast,the center of the unbalanced term increases and moves toward the northeast,and the vortex moves to the same direction.(3)When the shear line develops toward the low vortex,the shear deformation and the expansion deformation increase the interaction between the shear line and the low vortex.The shear line gradually develops into a cyclonic circulation and further forms a closed low vortex.When the low vortex forms,the shear deformation plays a major role,and when the low vortex develops,the role of the shear deformation and expansion deformation are equivalent.Shear deformation which makes the vorticity increase and is conducive to the formation of spiral convergence and rising structure,and the expansion deformation makes the convergence enhance which is favorable for the formation of the closed low vortex,and the inclined structure of deformation field determines the structure of the low vortex is the same.When the deformation and vorticity conversion index VDI value increases,indicating the interaction between the vortex and the shear line is enhanced,which is conducive to the formation and development of the vortex system,the vortex always moves toward to the center of the VDI.(4)The shear line moves toward to the direction where the convergence is enhanced,and the movement trend of shear line and the vortex are consistent in the meridional direction.The strong cold air is favorable for the shear line moves southward,when the warm and humid southwest airflow is weak,or the subtropical high ridge line is southward,or the anti-cyclone in the north of the shear line and the vortex strengthens and move southward,and the shear line is located in the high-altitude jet inlet zone and is accompanied by the southward movement of the jet stream,which are all beneficial to the shear line southward movement.(5)When a cyclonic circulation is formed on or near the transverse line,generally accompanied by the enhancement of southwest wind in the south of the shear line,then in this case the cyclonic circulation is always eastward movement,the eastward shift of the cyclonic circulation is accompanied by an increase in its strength,which is conducive to the formation and development of low vortex.