Distribution Characteristics And Causes Of Different Types Of Low Vortices On The Qinghai-Tibet Platea

Tibetan Plateau Vortices are important weather systems that affect precipitation over the Tibetan Plateau and downstream weather.Based on the reanalysis data provided by ECMWF and the soil moisture and sensible heat flux data provided by the Global Land Assimilation System dataset(GLDAS),the basic spatiotemporal variation characteristics of the Tibetan Plateau Vortices are determined using objective identification methods.This study clustered the Tibetan Plateau Vortices by different dynamic circulation types by SOM classification and explored the dynamic circulation background of the classified Tibetan Plateau Vortices in the midwestern Tibetan Plateau and their relationship with thermal factors,such as sensible heat and soil moisture.The main conclusions are as follows:(1)The Tibetan Plateau Vortices are mainly distributed in the midwest Tibetan Plateau,and the interannual change in this region is significant.And from the higher time resolution,it can be seen that the number of Tibetan Plateau Vortices shows strong diurnal variation.The results showed that Tibetan Plateau Vortices in the midwest Tibetan Plateau exhibited an increasing trend from May to August,its climate trend rate had increased by 1.3 per 10 y.(2)Both the dynamic and thermodynamic conditions could stimulate the generation and development of Tibetan Plateau Vortices.Tibetan Plateau Vortex occurrence is affected by various dynamic factors and circulation types.The SOM cluster analysis of circulation classified four circulation patterns affecting Tibetan Plateau Vortices: shortwave trough type,longwave trough type,shear line type,and plateau anticyclone type.The numbers of shortwave trough type and longwave trough type were the first and second largest.In terms of spatial distribution,shortwave trough type and longwave trough type often occurred in the central Tibetan Plateau,while the shear line type and plateau high pressure type usually appeared in the southeastern.Shortwave trough type and longwave trough type Tibetan Plateau Vortices occurred in front of the trough,but the circulation system of the longwave trough type Tibetan Plateau Vortices was deeper.The shear line type Tibetan Plateau Vortices were controlled by two high-pressure anomalies in the eastern and western regions at 500 h Pa,which affected the atmospheric instability and were conducive to the generation and development of Tibetan Plateau Vortices.Plateau anticyclone type had no notable trough,shear,or disturbance effects in the circulation,which requires further exploration of their mechanism.(3)Thermal factors,sensible heat,and soil moisture affect the formation of Tibetan Plateau Vortices over the Tibetan Plateau.Shortwave trough type,longwave trough type,and shear line type Tibetan Plateau Vortices were positively abnormal with the sensible heat flux,whereas the plateau anticyclone type Tibetan Plateau Vortices were negatively abnormal with the sensible heat flux.As a key factor modulating heating over the Tibetan Plateau,soil moisture was a negative anomaly in the shortwave trough type and longwave trough type Tibetan Plateau Vortices;the shear line had a positive relationship with the soil moisture.The soil moisture in plateau anticyclone type portrayed west-increase and east-decrease anomaly patterns.In most cases,the Tibetan Plateau Vortex frequency was positively correlated with the sensible heat and negatively correlated with the soil moisture.The model simulation confirmed this view.On the one hand,the change of soil moisture affects the intensity of the Tibetan Plateau Vortex.In the key areas of the Tibetan Plateau,the intensity of the Tibetan Plateau Vortex decreased with the increase of soil moisture.On the other hand,the change of soil moisture can also change the temperature gradient through the soil moisture gradient,affecting the location of the Tibetan Plateau Vortex.