Numerical Simulation Of The Influence Of The Altitude Of The Atmospheric Boundary Layer Of The Qinghai-Tibet Plateau On The Plateau Vortex

Based on the CERA-20 C data from European Center and the plateau vorticity data set which are counted based on ERA-Interim data,this paper analyzes the climatic characteristics of the diurnal variation of the boundary layer height over the Qinghai-Tibet Plateau from 1981 to 2010.Based on the characteristics of the plateau vortex in the diurnal variation of 1981 ~ 2010 statistical analysis.Influence of the height of boundary layer on Tibetan Plateau Vortex's formation in summer was further explored through correlation analysis and other methods,and verified using WRF3.7.1 mode.The main research results of this paper are as follows:(1)The high BLH value area of the Qinghai-Tibet Plateau is in an area with an altitude of more than 5000 m,where Nyima and other places are the diffusion source of the high value area of the boundary layer.From 9:00 to 12:00 local time,the increase of BLH was 948.67m/3h;from 15 to 18,the drop was 760.02m/3h,15:00 was the maximum,and the 30-year average maximum was 1982.764 m.The maximum was up to 2901.21 m,high and low at night.The BLH on the west slope of the plateau is the largest in spring and autumn,the hinterland is the largest in winter,and the BLH on the east slope is low,with a small variation.The spring plateau hinterland is in a melting period of snow,taking away surface heat,and the spring air surface temperature is lower.The height of the boundary layer is negatively correlated with surface air temperature in spring,while the relative humidity in summer is wavy,and the minimum value of relative humidity gradient corresponds to the top of the boundary layer.The height of the boundary layer is higher in spring than in summer.When the height of the boundary layer is the highest,the plateau boundary layer usually alternates between ascending motion and subsidence motion,providing certain dynamic conditions for the development of the boundary layer.(2)The generation and dissipation of plateau vortices are different at different times.The most frequent time for plateau vortex generation is local time at 18 o'clock and local time at 21 o'clock,accounting for 72.36% of the total;the plateau vortex dissipates the most time at 06 o'clock local time and place.At 12:00,the total proportion is 63.49%.The main origin of the plateau vortex is north of the Tibetan Plateau,and northern Tibet is particularly concentrated.The most frequent occurrence of high altitude vortex at 18 o'clock corresponds exactly to the time at which the height of the boundary layer decreases most rapidly.The northern part of the northern Tibetan Plateau where the source is generated corresponds to the most rapid zone where the height of the boundary layer decreases.It can be seen that there is a significant negative correlation between the height of the boundary layer and the formation of the plateau vortex.According to the conservation theory of the potential eddy,when the height of the boundary layer decreases,the height of the atmospheric column increases,and the vorticity increases accordingly.On the one hand,the appearance of the weather process will disperse the development of the boundary layer.On the other hand,the height of the boundary layer will decrease rapidly after the evening,and the convective process will be rapidly weakened.The atmosphere will be in a stable state,which is more conducive to the generation and development of mesoscale weather systems.(3)Using WRF3.7.1,a typical eastward migration plateau vortex was numerically simulated in 2016.The control experiment can well simulate the formation,development and dissipation of the plateau vortex,and simulate the precipitation during the development of the plateau vortex.Increasing the critical Ri index can increase the height of the boundary layer,and the height of the boundary layer is smaller at the increased height of the daylight than at night.The vortex of the plateau is formed at night and matures to reach a large value of vorticity.However,in the convective phase where the boundary layer of the day time is highly developed,the vortex of the plateau vortex is slightly reduced even during the development and maturation.At the same moment,the plateau vortex movement path selects the area where the boundary layer height is relatively low to move.In the control experiment,the plateau eddy area appears as a deep low-level convergent high-level divergence,accompanied by a strong upward movement,which is conducive to the development of the plateau vortex,and the dissipative process is the opposite.After the increase of the height of the boundary layer,the divergence of the high-level divergence at the time of the formation of the plateau vortex is not obvious and there is no obvious vertical movement process.In the mature stage,the low-level convergence is shallow and the vertical movement shows a complex rise.The sinking movement is not conducive to the development of the plateau vortex.Experiments show that the increase of the height of the boundary layer will destroy the divergence distribution of the high-level divergence at the lower level,and the complex layer of rising and sinking movements in the boundary layer will inhibit the development of the vortex.