A Comparative Study On The Atmospheric Circulation Characteristics Of Plateau Vortices In The Years With Frequent And Less Frequent Occurrences

The plateau vortex is a unique weather system on the Qinghai-Tibet Plateau.It often appears in the summer and is one of the main precipitation systems on the plateau.Sometimes the plateau vortex that has removed out of the plateau will bring heavey rain and other severe weather to some areas.Therefore,studying the plateau vortex has a certain significance for the weather forecast.Based on Lin Zhiqiang's plateau vortex dataset,this paper analyzes the characteristics of plateau vortex generation from 1986 to 2015,studies the differences of atmospheric circulation in june of the plateau vortex multi-year and less-year by using the reanalysis data and regional climate model.Then find the relationship between the plateau vortex and some weather systems,and analyzes the possible causes of these differences,draws the following conclusions:(1)From 1986 to 2015,an average of 69 plateau vortices were generated per year,showing an increasing trend,with more occurrences from May to August,most in June,and second in July.In July,the plateau vortex averaged 13.2 per year,mainly distributed between 75°-100°E and 28°-36°N.The number of plateau vortices generated in the west of 90°E accounted for 74.68%,which is the concentrated area of plateau vortex formation.(2)In multi-year,South Asia high pressure is located above the Qinghai-Tibet Plateau on average,and the intensity is relatively large.The South Asia high-pressure center is located on the Iranian plateau with a small intensity in less-year.The 500 hPa Qinghai-Tibet Plateau is a north-ridge-and-south-trough pattern circulation,and the western Pacific subtropical high westward ridge point is eastward,the Iranian high-pressure intensity is weak.The north ridge of the Qinghai-Tibet Plateau is weak in less-year,and the western Pacific subtropical high west ridge is westward,with strong intensity and strong Iranian high pressure.The anticyclone circulation in the northern part of the Tibetan Plateau and the configuration of the southern cyclonic circulation are conducive to the formation of plateau vortices.The Qinghai-Tibet Plateau is characterized by updrafts,low-level convergence,high-level divergence.In multi-year year,more moderately low-level convergence and high-level divergence in the mid-western part of the Qinghai-Tibet Plateau,and its corresponding ascending motion is also strong,the entire layer of atmospheric heat sources is strong,the layers in the vertical direction of the central and western parts of the Qinghai-Tibet Plateau are heat sources.In less-year,the entire layer of atmospheric heat sources is weak,and the lowerlayer in the vertical direction of the central and western regions is the heat source,and the upper layer is the heat sink.(3)The atmospheric heat source on the Qinghai-Tibet Plateau may has impact on the movement and maintenance of the South Asian high pressure.The increase of atmospheric heat sources in the Qinghai-Tibet Plateau is relatively fast,which is conducive to the movement of the South Asian high-pressure center to the Qinghai-Tibet Plateau;the strong atmospheric heat source increases the intensity of the South Asian high pressure,and is also conducive to the maintenance of the South Asian high-pressure center in the western part of the Qinghai-Tibet Plateau.The South Asia High Pressure Center is on the Qinghai-Tibet Plateau,which is conducive to the formation of low-level convergence and high-level divergence on the Qinghai-Tibet Plateau.The strong South Asia high-pressure center maintains on the Qinghai-Tibet Plateau and enhances its ascending motion below.The increase and decrease trend of the ascending motion is the same as the vertical change trend of the atmospheric diabatic heating.In multi-year,due to the early formation of the India-Bangladesh Bay low,more water vapor was transported to the Qinghai-Tibet Plateau.(4)By using regional climate model simulation,the characteristics of the plateau vortex generated in July of 1999(multi-year)and 2015(less-year)are roughly consistent with the statistical results.In multi-year,the ground heat source is strong in the early stages.The sensible heat on the ground has a certain influence on the formation of the plateau vortex,but mainly affects the atmospheric circulation.In multi-year,Tibetan Plateau has strong relative humidity in the plateau vortex-prone area,strong ground latent heat,and weaker outgoing long-wave radiation,indicating that under strong convection,the heat exchange of water vapor increases the convective instability in the middle and lower layers,and further enhancing the cyclonic circulation in the lower layer.It is an advantageous background condition for the generation of plateau vortices.