China Meteorological Administration Training Centre
The Tibetan Plateau transverse shear line (TPTSL) is one of the main weather systems over the Tibetan Plateau. Based on the ERA-5 reanalysis datasets provided by the European Centre for Medium-Range Weather Forecasts (ECMWF), 14 cases of TPTSL which causes heavy rainfall and generates in June-August with a lifetime of 38 hours are selected and composited to reveal the impact of dynamic and thermodynamic forcing on the intensity evolution of TPTSL s. The results are as follows. (1) At 500hPa, the TPTSL generates in the saddle field between the Iran high and the western Pacific subtropical high, and is located in the low-pressure center contoured by 584dagpm and warm center contoured by 272K, to the north of the specific humidity center. At 200hPa, the TPTSL is located in the northern margin of the South Asian High and to the south of the entrance region of the westerly jet stream. (2) The intensity of TPTSL at 500hPa shows an obvious diurnal variation with the strongest at 23LT and the weakest at 13LT (LT=UTC+6h). (3) The vorticity budget reveals that the variation of the divergence at the upper and the convergence at the lower layers over the Tibetan Plateau is indicative of the intensity of TPTSL, and the vorticity at 500hPa gets maximum 3 hours later than that of the convergence. (4) Potential vorticity (PV) increases with the development of the TPTSL. The PV budget shows that the water vapor and diabatic heating play an important role in the generation and evolution of the TPTSL. The enhanced sensible heating leads to an intensified ascent. With sufficient water supply, the latent heating releases and the diabatic heating center rises to the middle layer, which is favorable for the generation and development of the TPTSL.