Diagnostic Study Of Plateau Low Vortex Shear Line Affecting Heavy Rainfall In Yunnan

This paper is based on the MICAPS historical weather map of the China Meteorological Administration from 2012 to 2017,the ERA-Interim of the European Medium-Range Weather Forecast Center(ECMWF),the monthly average analysis data,and the Global Data Assimilation System(GDAS)data provided by the National Center for Environmental Prediction(NCEP).Three low-vortex shear lines of the Tibet Plateau were selected from the measured data of 124 stations in Yunnan,and they were analyzed and compared to discuss the characteristics of the strong precipitation in Yunnan and their differences.Finally,the HYSPLIT model was used.Clustering backward trajectory analysis.The main conclusions are as follows:(1)In the circulation situation,the strengthening of the South Asian high pressure and the 200 hPa position above the plateau low vortex shear are in the west wind rapids.These two factors play a vital role in the development of the plateau low vortex shear,and lack one of the conditions.It is possible that the plateau low vortex shear will not move and develop.The two conditions have a great possibility that the plateau low vortex shear will move and develop,and there is no plateau low vortex shear developed to the eastern part of the Qinghai-Tibet Plateau.The impact is small,and it is likely that the plateau low vortex shear that moves to the eastern part of the Qinghai-Tibet Plateau will have an impact on strong precipitation in Yunnan.In the process of influencing the strong precipitation in Yunnan,guiding the northern Qinghai-Tibet Plateau cold advection into the south and the positive vorticity advancing to Yunnan is an important means for the plateau low vortex shear to affect the strong precipitation in Yunnan.And the plateau low vortex shear affects the strong precipitation in Yunnan,and other weather systems generally cooperate with each other.(2)Plateau low vortex shear dynamic structure characteristics affecting strong precipitation in Yunnan:it has a strong positive vorticity center and its relative humidity center position coincides with it.The vortex inner layer is unstable and the atmospheric height is high.The vorticity distribution area is large.The vertical helicity has a good distribution of rainbands in the strong plateau of Yunnan due to the low vortex shear in the reaction plateau.(3)Plateau low vortex shear affects the source of water vapor in Yunnan's strong precipitation.There are three main routes:1.From the Bay of Bengal,the westward airflow enters Yunnan.2.The water vapor in the South China Sea enters the Yunnan region along the southeast airflow around the western Pacific subtropical high.3.The water vapor on the Qinghai-Tibet Plateau descended from the Qinghai-Tibet Plateau into the Yunnan region.The water vapor in the first two paths has a higher proportion of total water vapor,and the third path has less water vapor.(4)The WRF model simulates the strong precipitation process in Yunnan from June 29 to July 4,2017.