The Characteristics Of The Near-surface Thermal Depression In The Qinghai-Tibet Plateau And Its Influence On The Plateau Vortex

The Tibetan Plateau vortex is a unique weather system that created by the thermal,dynamic and large terrain effect of the Qinghai-Tibet Plateau.Its occurrence,development and eastward migration will have an important impact on precipitation in the plateau and downstream areas of the plateau.In summer,Tibetan Plateau heat low is stable and strong,which promotes the convergence of the surrounding atmosphere to the plateau hinterland and transports the sensible heat to the upper atmosphere of the plateau.This paper discussed the influence of heat low intensity change on the plateau vortex from the climatological point of view.Using the ERA-Interim reanalysis data from 1988 to 2017,the characteristics of the thermal low-pressure structure were refined,and the influence of ground heating on its establishment and development was discussed.The heat low is strongest at its maturity stage,with the longest duration and the widest range,so that the Tibetan Plateau hear low index is calculated during this period,the "Low-vortex objective identification data set of the Qinghai-Tibet Plateau" is used to compare and analyze the characteristics of Tibetan plateau vortex source,path,frequency,intensity,cold and warm nature,area,duration in the summer heat low strong years and weak years,its influence mechanism is discussed.The main findings are as follows:(1)According to the circulation situation,the geopotential height anomaly field and the multi-year statistical analysis of the heat low intensity,the near-surface heat low of the Qinghai-Tibet Plateau is divided into the primary stage(May),the maturity stage.(June-August)and the weak stage(September).The heat low range in the primary stage is small and lack of independence,and it is connected with the low pressure area of India;the heat low in the mature stage is stable and strong,with widest horizontal and vertical range;in the weak phase heat low is rapidly weakened,and the low-pressure zone is narrowed and lifted northward.(2)The thermal low pressure can reach 500hPa-450 hPa,with positive vorticity and negative divergence area.It is controlled by updraft and has a warm and dry structure.The closer to the ground,the warm and dry features are more obvious.In summer,the latent heat released by the precipitation heats the atmosphere above the plateau,which is beneficial to the development of heat low.The strong latent heat in the eastern part of the plateau makes the hot low pressure range eastward.extend.(3)The Tibetan Plateau hear low index of the plateau is significantly negatively correlated with the number of plateau vortices.The frequency of plateau vortex is high(low)while heat low is strong(weak).The source of plateau vortex is concentrated in the central and western regions of the plateau.In heat low strong years,the Tibetan Plateau vortex number origin in the west and middle range of Plateau is more than heat low weak years.Low-level convergence,high-level divergence,strong upwelling over the plateau,making the atmosphere circulation,and water vapor conditions in heat low strong years are more conducive to the generation of Tibetan Plateau vortex.(4)In heat low strong(weak)years,the Tibetan Plateau vortex intensity is stronger(weak),the warm vortex is more(less),and the area is larger(small);the Tibetan Plateau vortex intensity in the initial stage is sensitive to the ground sensible heat,accompanied by the plateau vortex continues to develop eastward,and the influence of ground sensible heat is weakened;In heat low strong years,the western part of plateau has strong sensible heat flux which cooperates with the deep warm and humid center over the eastern part of the plateau,making the warm vortex can keep its high warm core temperature in its whole lifetime.(5)The number of long lifetime Tibetan Plateau vortices(?60h)is relatively high in heat low weak years,which may be related to latent heat and cold advection.The latent heat in the plateau of the heat low weak years is significantly stronger.,The southern and eastern parts of the plateau are mainly controlled by cold advection,which has a positive impact on the generation of long lifetime Tibetan Plateau vortex.