Dynamic and numerical study of waves in the Tibetan Plateau Vortex

Abstract

In terms of its dynamics, The Tibetan Plateau Vortex (TPV) is assumed to be a vortex in the boundary layer forced by diabatic heating and friction. In order to analyze the basic characteristics of waves in the vortex, the governing equations for the vortex were established in column coordinates with the balance of gradient wind. Based on this, the type of mixed waves and their dispersion characteristics were deduced by solving the linear model. Two numerical simulations with triple-nested domains—one idealized large-eddy simulation and one of a TPV that took place on 14 August 2006—were also carried out. The aim of the simulations was to validate the mixed wave deduced from the governing equations. The high-resolution model output data were analyzed and the results showed that the tangential flow field of the TPV in the form of center heating was cyclonic and convergent in the lower levels and anticyclonic and divergent in the upper levels. The simulations also showed that the vorticity of the vortex is uneven and might have shear flow along the radial direction. The changing vorticity causes the formation and spreading of vortex Rossby (VR) waves, and divergence will cause changes to the motion of the excitation and evolution of inertial gravity (IG) waves. Therefore, the vortex may contain what we call mixed inertial gravity-vortex Rossby (IG-VR) waves. It is suggested that some strongly developed TPVs should be studied in the future, because of their effects on weather in downstream areas.