Characteristics Of Severe Convective System Over Yunnan Plateau And Its Relationship With Lightning Activity

Based on the data of global lightning positioning network(WWLLN),Yunnan ground flash positioning network(LLS),radiosonde data,Fengyun satellite data and radar data,this paper explores the temporal and spatial distribution characteristics of lightning activities in Yunnan Province from 2010 to 2018,focusing on the cloud top brightness temperature(TBB)and radar echo parameters of different types of severe convective systems in Gaoyuan area of Yunnan Province from 2017 to 2019 The main conclusions are as follows:(1)On the whole,the spatial distribution of lightning activity in Yunnan province is more in the south than in the north and more in the east than in the west,which is closely related to the topography and climate region of Yunnan province.Lightning occurs frequently in the gentle and open Yunnan-guizhou plateau and the southern river valleys,while lightning activity is rare in the hengduan mountain area and alpine valleys,indicating that the slope of the terrain is more conducive to the occurrence of lightning than the altitude.In summer,the east asian monsoon deep in the interior makes the lightning in the east Yunnan region with high latitude,and the lightning activity in most areas in the north of central Yunnan shows a single peak monthly distribution.In spring and autumn,due to the influence of the southwest monsoon,the lightning peak appeared in the southern Yunnan region at a lower latitude,and the distribution of lightning activity months also presented a bimodal pattern.(2)In summer,Yunnan was affected by the shift of the subtropical high to the west and northward,and combined with the low-pressure cyclone center,shear line and amplitude line near the formation,as well as the high-energy and high-humidity conditions formed by the peripheral southeast monsoon and southwest airflow,the uplift dynamic conditions and water vapor conditions conducive to the occurrence of strong convection were formed.The type of the strong convective system is closely related to the movement of the subtropical high from west to north.When the sub-high line passes through the interior of Yunnan,the strong convection is arranged in a strip along the outside of the sub-high line,forming a multi-cell thunderstorm or squall line system.When the secondary height completely covers Yunnan,the convective system is mostly monomer thunderstorms.The location of the sub-high line also affects the moisture transport on the ground.The advection inversion at low altitude can promote the convection,while the radiation inversion at high altitude can inhibit the development of the convection.The ground flash activity of the strong convection system occurs frequently near the sub-high line,shear line and convergence line,and the occurrence of extreme weather is also related to the density distribution of ground flash.The ground lightning activity is mainly concentrated in the plateau area of Yunnan province.(3)The density distribution of positive and negative ground flicker has a good correlation with the cloud top temperature in the convective system.In the region of-40?-60?,the ground flash frequency increases with the decrease of TBB,and the corresponding TBB of negative ground flash is lower than that of positive ground flash.A region with a large temperature gradient at the top of a cloud.It is worth noting that,under the combined action of topography and monsoon,lightning of summer thunderstorms in central yunnan often occurs on the east and south sides of convective clouds.Positive and negative ground lightning activity can characterize the evolution of strong convective system,strong convection system of the four types,positive and negative to flash frequency and TBB over time and the changing rule of basic consistent,negative to dominate,showed activity in the early stage of the development stage and mature stage,is to flash less and basic became active in the mature stage.(4)The reflectivity intensity of thunderstorms on the Yunnan plateau is generally weak compared with that in the central,eastern and southern regions of china,which is consistent with the research results on the intensity of thunderstorms on the qinghai-tibet plateau.In terms of spatial distribution,the ground flash is mainly concentrated in the strong echo region with combined reflectance of 35?50dbz.The combined reflectance area of 35 dbz,40dbz and 45 dbz increases or decreases with the increase or decrease of the basic anywhere flash frequency.The strong echo of cr>30dbz is mostly concentrated at the leading edge of the thunderstorm system.The height of negative ground flash is higher than that of positive ground flash,and the height range of positive ground flash is larger than that of negative ground flash.The density of negative ground flash is basically uniformly distributed above and below 15 km,while the density of positive ground flash mainly occurs near the height of 13 km.(5)In flash frequency change,lightning and high echo area and echo top has a good corresponding relation,and relevance to echo top high than echo area,lightning frequency and strong echo area for the highly correlated,the changes of average correlation coefficient can reach 0.82 ? 0.89,and echo top height is significant correlation,the correlation coefficient between 0.58 ? 0.78.The size of correlation coefficient r mainly depends on the size of echo intensity and the increase or decrease of lightning frequency,and has no obvious correlation with the type of thunderstorm.The increase of the lightning frequency is more consistent with the change rule of the increase of the radar echo factor.When the growth(decrease)rate of the local flash number is less than the change rate of the echo area(Echo Top),the correlation between the two decreases.