The relationship between cloud-to-ground lightning spatial distribution and topography in Guangzhou

According to the Guangdong lightning location system (GDLLS), the data of cloud-to-ground (CG) lightning in Guangzhou from March to October of 2016–2018 are summarized and analyzed combined with digital elevation model (DEM) from ASTER GDEM V2. Frequency and intensity of three years CG lightning decrease gradually. CG lightning in Guangzhou is mainly negative. Negative return stroke percentage of most areas exceeds 80 % except for center part of Guangzhou. Most areas terrain of Guangzhou is plain, and mountainous areas are mainly distributed in five north districts. By dividing CG lightning data located in five north districts into groups according to elevation, return stroke density curve shows an irregular U shape with elevation rise while negative mean peak current and negative stroke percent curves rise on the whole. Comparing terrain and CG lightning data of 7 selected regions, CG lightning activity of mountainous areas is more frequent with higher negative stroke percent compared to flat ground without much terrain relief. Topographic regions with a central low elevation flanked by higher elevations on both sides are termed U-shaped areas. This structural configuration may suggest that atmospheric convection is enhanced within these regions, resulting in higher lightning strike density. Through thunderstorms traversing paths analysis, it is found thunderstorms usually occur in areas with great relief at the junction of mountains and flat ground. And thunderstorms generally move in the direction of the mountains extending. If the thunderstorms are strong enough, they may climb through the mountains. When thunderstorms encounter a U-shaped area, they tend to traverse to it.