Spatial And Temporal Distribution Of Lightning Over Guangxi Based On Observations From Lightning Mapping Imager Onboard Fengyun Satellite

Lightning is a common natural discharge phenomenon between clouds,between clouds and ground,or between different parts of the cloud’s body.As a sign of strong convective activity,there is a close relationship between lightning and the natural environment.The analysis of the spatiotemporal distribution characteristics of lightning and the study of the relationship between the spatiotemporal distribution characteristics of lightning and the natural environment are of great significance for understanding the law of lightning activity and improving the abilities to prevent damages and harms from lightning strikes.As an area with a high incidence of lightning activities,Guangxi has lightning activities in the whole region.Therefore,improving the awareness of lightning activities can help improve the government and people’s capabilities of disaster prevention and mitigation related to lightning strikes,and reduce the damage to life and property caused by lightning activities.This thesis mainly analyzes the lighting observations from groundbased lightning observation network Advanced Direction and Time-of-arrival Detecting(ADTD)and the Lighting Mapping Imager(LMI)aboard the Fengyun-4A(FY-4A)geostationary meteorological satellite,and discusses the spatiotemporal distribution characteristics of lightning as well as the influence of topography and geomorphology on the spatiotemporal distribution characteristics of lightning in Guangxi Zhuang Autonomous Region,discuss the similarities and differences between FY-4 Lighting Mapping Imager and ADTD in Guangxi lightning observation,and summarize the spatial and temporal distribution pattern of lightning activity in Guangxi..The main conclusions of this thesis are as follows:(1)Lightning activity in Guangxi occurred all over the region,and the high-incidence area are concentrated in the southeast of Guangxi in the area of Liuwandashan Mountain-Darong Mountain-Goulou Mountain-Yunkai Mountain-Dagui Mountain,the Youjiang River Valley in central Baise and the Zuojiang River Valley in the middle of Chongzuo,the Shiwandashan Mountain in Fangchenggang and the Qinzhou Bay,and the mountainous areas of Hechi-LiuzhouGuilin in northern Guangxi.The spatiotemporal distribution of lightning activities shows pronounced variation and characteristics in different years and seasons.The lightning frequency varies greatly in the three years from 2018 to 2020,with 2019 having the most lightning.The active period of lightning is from April to August,which corresponds to the rainy season in Guangxi.Lightning can occur throughout the day,even between 8 a.m.and 12 p.m.with a small amount of lightning activities.Usually,lightning is mainly active from the afternoon to the early hours of the next day.Flashes often become active in the early afternoon with peak in the afternoon.At night,lightning activities are stronger in northwestern and northern Guangxi.(2)The two types of lightning data show unity in the spatial and temporal distribution of Guangxi.In terms of time,LMIE detects more lighting activities than ADTD data in the nighttime.Spatially,the density distribution of ADTD is relatively scattered,and the density distribution of LMI is more continuous and spatially wider.In the northern part of Hechi-Liuzhou-Guilin,the Baise Youjiang River Valley,and the Chongzuo Zuojiang River Valley,the LMI detected more intense lightning activity.The two types of lightning data showed a discontinuous correlation.The correlation coefficient between the two lightning bolts was higher in the area with higher lightning density.Where the density of lightning is low,the correlation between the two types of lightning observations is low.As a traditional ground-based lightning instrument,ADTD lightning observer has a relatively complete observation ability for ground lightning.The LMI on board the FY-4satellite observes the total flash in the whole area from a space-based perspective,and the observation capability will be relatively comprehensive.(3)There was an annual variation in the lightning incidences related to altitude,with the lightning density being high at low altitudes in 2018,and high at medium and high altitudes in2019 and 2020.Additionally,the lightning density also has annual differences over the different slopes.Lightning density is higher in the slope of 0-2° in 2018,and is the same between 2-10° in2019,and is high with 10-15° in 2020.In terms of the lightning density related to elevation and slope,there was a well agreement between ADTD and LMI observations.There are similarities and inconsistencies in the density ratio of the two types of lightning data related to the underlying surface.During the three years’ period from 2018 to 2020,the lightning density ratio of forest was always higher than area ratio of forest,but the density of cultivated land was always lower.Natural grassland sees low lightning density in all years,except for a slightly higher proportion of density detected by ADTD and LMIG in 2020.LMI data has a high proportion of lighting density over water areas,while ADTD has low proportion of lighting density over water areas during the same period.(4)The causes of lightning activity in Guangxi vary from geographical location and different seasons.The high incidence of lightning activity coincides with the time of the flood season in South China,which should be caused by the active warm and humid air masses in Guangxi during the rainy season,when the active convective activities were caused by the interactions of cold and warm masses.In spring,warm and humid air currents meet cold air to cause convection,while summer is affected by monsoon and subtropical high pressures and typhoon activities.In the Zuojiang and Youjiang River Valleys,intensive lightning activity is prone to form due to changes in solar radiation and the uplift of air currents affected by topography.In Shiwandashan Mountain,it is more likely to form convections due to thermal properties difference between the land and the sea,warm and humid airflow on the sea surface being blocked and lifted by the mountains.These convection usually bring lightning.Lightning often starts to be active in the early afternoon of the day until the early morning of the next day.The reason is that the underlying surfacee is heated by solar radiation in the afternoon,which causes strong convection after the temperature rises.