Impact of Dynamic and Thermal Forcing on the Intensity Evolution of the Vortices over the Tibetan Plateau in Boreal Summer

Abstract

The Tibetan Plateau Vortex (TPV) is one of the main weather systems causing heavy rainfall over the Tibetan Plateau in boreal summer. Based on the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) reanalysis datasets provided by the National Aeronautics and Space Administration (NASA), 8 cases of TPV over the Tibetan Plateau generated in June-August with a lifetime of 42 hours are composited and analyzed to reveal the impact of dynamic and thermal forcing on the intensity evolution of TPVs. The results are as follows. (1) The TPVs appear obviously at 500 hPa and the TPVs intensity (TPVI) shows an obvious diurnal variation with the strongest at 00LT and the weakest at 12LT (LT=UTC+6h). (2) A strong South Asia High at 200 hPa as well as a shrunken Western Pacific Subtropical High at 500 hPa provide favorable conditions for the TPVI increasing. (3) The vorticity budget reveals that the divergence is indicative of the variation of the TPVI. The TPVI decreases when the convergence center at 500 hPa and the divergence center at 200 hPa lie in the east of the TPVs center and increases when both centers coincide with the TPVs center. (4) Potential vorticity (PV) increases with the enhancement of the TPVI. The PV budget shows that the variation of the TPVI is closely related to the diabatic heating over the Tibetan Plateau. The increased sensible heating and radiative heating in the boundary layer intensify the ascent and latent heating release. When the diabatic heating center rises to 400 hPa, it facilitates the development of the TPVs.