Numerical experiments and dynamic diagnosis of the upper-level jet stream impact on the Tibetan Plateau shear line

Using the NCEP 1°×1° FNL analysis data and the mesoscale model WRF, numerical experiments have been conducted to simulate a Tibetan Plateau shear line process. The study focuses on the impact of the upper-level jet stream intensity on the Tibetan Plateau shear line. In combination with the ω equation, factors affecting the ascending motion in the Tibetan Plateau shear line are also analyzed. The results show that the intensity of the upper-level jet stream has an important influence on low-level wind fields. The increases in jet stream will intensify the wind shear along the Tibetan Plateau shear line, and the shear line will become longer. Meanwhile, the enhancement of the upper-level jet intensity is also favorable for the convergence of water vapor along the Tibetan Plateau shear line. The upper jet can affect positive vorticity, convergence and ascending motion along the Tibetan Plateau shear line by influencing the vertical configuration of lower-level convergence and upper-level divergence. The diagnostic analysis of the ω equation shows that the Laplace term of temperature advection plays a dominant role in the ascending motion along the Tibetan Plateau shear line, and the low-level warm advection is favorable for the development of ascending motion along the shear line. The influence of the variation of upper-level jet stream intensity on the differential term of the vorticity advection is greater than that of the Laplace term of temperature advection, and the enhancement of the upper-level jet intensity will enlarge the positive contributions of the differential vorticity advection term and the temperature advection term, which is more favorable for the development of ascending motion and the maintenance of the Tibetan Plateau shear line.