The Structural Characteristics Of The Shear Line Of The Qinghai-Tibet Plateau And Its Relationship With The Non-adiabatic Heating Of The Plateau

The article used the ERA-Interim reanalysis dataset of 4 times a day in June—August 1981—2016 with a resolution of 1 °× 1 °,based on three parameters which are the meridional shear of zonal wind,the zero line of zonal wind speed and the relative vorticity,and the automatic identification of the meridionally-oriented shear lines over the Tibetan Plateau(MOSLs),a total of 13 cases of MOSLs between 33-35 °N were selected.The structure and evolution characteristics of MOSLs and the distribution and evolution characteristics of the non-adiabatic heating in the vicinity of MOSL was studied based on the synthetic analysis technique.The complete form vertical vorticity tendency equation was used to diagnose and study the mechanism by which non-adiabatic heating affects the evolution of MOSL,the study showed that:(1)MOSL was located in the range of 80°—100°E in the main body of the plateau.The life history was nearly 4 days.The east-west trend was horizontally distributed at500 h Pa and the horizontal scale could reach 2000 km.The vertical direction extended to 480 h Pa above the plateau.Thickness up to 2km;The circulation background of MOSL was the circulation situation of the two-trough and two-ridge at high latitude at 500 h Pa,and the Western Pacific Subtropical High(hereinafter referred to as the WPSH)and the Iranian high were distributed on both sides of the Qinghai-Tibet Plateau.On the dynamic field,the strike direction of MOSL was consistent with the axis of the 500 h Pa positive vorticity belt,corresponded to the non-divergence zone,there were strip-shaped vorticity positive value area and the rising motion area near shear line;The positive vorticity zone near the plateau cross-cutting line could extend to 350 h Pa vertically,and the ascending motion extended to 200 h Pa,but the shear line was only about 480 h Pa,which was a shallow and baroclinic weather system,and exhibited the characteristics of tilting north with height.On the thermal field,MOSL was located near the temperature zero line;There was a high pseudo-equivalent temperature center between 600-500 h Pa on the south side of MOSL,which had a very obvious characteristics of high temperature and high humidity.The evolution process of MOSL was accompanied by the westward movement of the WPSH.When the development of the shear line was enhanced,the ascending motion in the vicinity increased,and the range and intensity of the positive vorticity band increased;When the dry cold air invaded MOSL,it would cause the shear line strength to weaken or even die.(2)The distribution and evolution of adiabatic heating affected the development and evolution of MOSL.In the vicinity of MOSL,the adiabatic heating intensity and relative vorticity intensity showed significant diurnal variation characteristics;The adiabatic heating of the whole layer integral near the shear line was characterized by the distribution of“south high and low north”,the maximum value of adiabatic heating of the atmosphere was near the height of 400 h Pa;When the layers in the vertical direction of the atmosphere were transformed into adiabatic heating,and the maximum value of adiabatic heating increased,the shear line then developed and strengthened.During the evolution of MOSL,adiabatic heating intensity evolution in was ahead of the shear line for 6 hours,so it had certain indication significance for the shear line strength change;In the process of the development of MOSL,the temperature vertical conveying process of adiabatic heating contributed the most.(3)In the contribution that affected the local variation of vorticity near MOSL,the spatial non-uniform heating effect was the largest.The height of the spatially non-uniform heating effect was positive at 600—500 h Pa near MOSL,the distribution and evolution characteristics of the vertical non-uniform heating effect were consistent with the spatial non-uniform heating effect,the maximum value of the vertical non-uniform heating effect was located at 500 h Pa;Horizontal non-uniform heating effect was dominated by zonal non-adiabatic heating.The vertical non-uniform heating effect near the shear line was enhanced and closed to the shear line,which was conducive to the development of the shear line.Therefore,the vertical non-uniform heating effect was one of the mechanisms for the development of MOSL;The increase of the latitudinal non-uniform heating gradient provided conditions for the formation of the front near MOSL.(4)MOSL was a water vapor gathering belt,when the convergence of water vapor to the shear line was enhanced,the development of the shear line was enhanced;The distribution of plateau atmospheric moisture sink in the whole layer near MOSL was characterized by the distribution of “south high and low north”;When moisture sink in the southern margin of the plateau developed to the north and reaches to the eastern section of the shear line,shear line was enhanced synchronously;When the water vapor was transported from the lower layer to the middle and upper layers,the shear line is also developed simultaneously;In the evolution process of MOSL,the vertical transport of specific humidity is the main contribution.