A Diagnosis And Numerical Simulation Of The Eastward Movement Of The Plateau Vortex

An obvious process of plateau vortex occurred in western China,in late July2014.In this paper,we used the NCEP FNL reanalysis data,the ground automatic and CMORPH fusion precipitation data,the weather satellite observation data,and the WRF model to study the plateau vortex process.On the one hand,we analyze the structural changes in the process of the plateau vortex during the eastward shift of the plateau vortex.On the other hand,We analyze the characteristics of the plateau vortex moving out of the plateau and causing heavy rain.Secondly,using the four cumulus convective schemes in the WRF model to simulate and compare the rainstorm process.Finally,Preliminary exploration of the influence of latent heat on the plateau vortex.The main research results are as follows:(1)At 12:00 on the July 28,the plateau vortex was generated in the shear flow field formed by the southerly airflow in the south of the plateau and the central easterly airflow.In the process of the formation of the plateau vortex,the South Asian High Pressure has played a catalytic role.(2)During the process of eastward plateau vortex,the change of vorticity field at500 h Pa reflected the change of vortex intensity of the plateau vortex.It can be divided into two stages: the first stage is the plateau vortex is generated,mature and weakening;the second stage is the plateau is weakening,enhancement,maintenance,disappearance.The vertical distribution of the vorticity,divergence and vertical velocity in the vortex region can reflect the enhancement or weakening of the dynamic characteristics of the plateau vortex.The divergence term in the vorticity equation has the largest contribution to the total vortex source,indicating that the maintenance of the mid-lower cyclonic convergence flow field in the atmosphere is the main influencing factor of the maintenance and development of the plateau vortex.(3)When the plateau vortex develops or is maintained east of the plateau,the cold area on the north side of the 500 h Pa plateau vortex promotes the development of the plateau vortex.The plateau vortex with 500 h Pa~300h Pa is warm,and above300 h Pa is cold.There is a positive correlation between the increase or decrease of the plateau vortex and the change of warmth intensity at 500 h Pa~400h Pa.The changes of the apparent heat source and water vapor sink near the low vortex and the change of the intensity of the low vortex have a good corresponding relationship,reflecting that both play an important role in the development of the plateau vortex.(4)During the rainstrom in the Sichuan Basin,the low-level 850 hPa in the rainstorm area has in the water vapor convergence area,a lot of convective instability energy has accumulated,the positive vorticity has developed,and the vertical upward movement has obviously increased.The water vapour sinking above the storm zone has been maintained and developed,indicating that the latent heat released during precipitation increases,heating the atmosphere,and the atmosphere in turn acts on the maintenance and development of the weather system,which is the reason why the heavy rain may be maintained.However,the vorticity advection is distributed at 700 h Pa in the lower part of the eastern and southeastern vortex during the period of heavy rainfall.Therefore,the positive vorticity in the lower layer develops,the cyclonic convergence in the wind field increases,and the vertical upward movement increases,which promotes convection and causes precipitation.This is the likely trigger of heavy rain.(5)Using the four cumulation schemes of KF,GD,SAS and BMJ in the WRF model to simulate the rainstorm shows: the location of precipitation belt simulated by the four cumulus schemes is more south than the actual situation,and the center of large precipitation is larger than the actual situation.The KF scheme simulates the shape of the precipitation belt relatively better than other schemes.With the increase of the model integration time,the simulation results of the four schemes are not ideal.(6)When the latent heat in the mode was turned off,the plateau vortices disappeared in the early period of the heavy rain,the precipitation significantly weakened,and the vertical structure of the plateau vortex also weakened significantly.It shows that latent heat plays an important role in the development of the plateau votex.