Large-scale backgrounds and crucial factors modulating the eastward moving speed of vortices moving off the Tibetan Plateau

Abstract

Tibetan Plateau vortices (TPVs) are major rain producer over the Tibetan Plateau, which trigger heavy rainfall in southwestern and eastern China when moving off the plateau. In this work, two groups of TPVs moving off the plateau are selected according to their eastward moving speeds. The features of the atmospheric dynamic and thermodynamic fields associated with the two groups of TPVs are compared, based on the final (FNL) operational global analysis data from the Global Forecasting System of the National Centers for Environment Prediction (NCEP). The results show that the large-scale circulations and heating fields have a close relationship with the moving speed of the TPVs. The TPVs move eastward faster when wider and stronger convergence at 500 hPa, divergence at 200 hPa and the related ascending motion are observed to the east of TPVs. In addition, the stronger and further eastward stretching unstable stratification and water vapor convergence, as well as the more intensive heating field above 500 hPa to the east of TPVs, correspond to larger eastward moving speed of TPVs. Furthermore, the crucial factors modulating the moving speed of TPVs are explored through potential vorticity (PV) budget analyses, in which the physical variables are partitioned into zonal means and disturbances. The convergence of the mean zonal winds and disturbance winds at 500 hPa, as well as the vertical distribution of disturbance heating to the east of TPVs are the crucial factors influencing the eastward moving speed of TPVs, among which the vertical distribution of disturbance heating is the most dominant.