## 3 The Lightning Hazard and Its Spatial and Temporal Activity Characteristics  
When lightning strikes, it generates a range of intense physical phenomena, including powerful electrical currents, potent electromagnetic radiation, severe shockwaves, and extreme heat. These effects have the potential to instantaneously inflict harm on people and property, ultimately culminating in adverse societal consequences [59]. Lightning can generally be divided into two categories. Cloud-to-ground (CG) lightening refers to lightning that hits the ground from thunderstorm clouds, while intra-cloud (IC) lightening refers to lightning that occurs in or between clouds, that is, all lightning that does not hit the ground. In particular, the CG lightning that occurs between clouds and the ground poses the most serious threat to ground objects and human beings. When utilizing lightning location data for the research of cloud-to-ground (CG) lightning, it is imperative to account for the contamination caused by intra-cloud (IC) discharges on the CG lightning detection network. A peak current threshold of <10 kA can be effectively employed as a screening criterion to mitigate the interference from IC discharges [60; 61]. This approach helps ensure more accurate and reliable results from the lightning detection network. Scholars have analyzed the spatiotemporal distribution patterns of IC and CG flashes in Beijing and the surrounding areas using an SAFIR3000 device, a device capable of observing total lightning flashes (Figure 4). The results indicate that CG lightning is primarily concentrated in the northeastern part of Beijing, northern Tianjin. The maximum density of CG flashes is approximately 30 flashes/km\({}^{2}\)-a. The spatial distribution of CG flashes is generally similar  
Figure 3: Schematic diagram of the initial process of triggering lightning with a wired rocket during the triggered lightning experiment: Field Experiment Base on Lightning Sciences, China Meteorological Administration [44]. The symbol + represents positive charge, and the symbol \(-\) represents negative charge. to that of cloud IC flashes, yet the maximum density of CG flashes is significantly lower, reaching only about 5 flashes/km\({}^{2}\)-a [62]. Overall, current research primarily focuses on analyzing the spatiotemporal characteristics of cloud-to-ground (CG) lightning flashes [36; 37; 39; 63; 64; 65; 66; 67; 68]. The lightning location data collected by the lightning detection network installed at the Korean Meteorological Administration (KMA) have been used to study the CG lightning activity over and around Seoul, the largest metropolitan city in South Korea, for the period of 1989-1999 [63]. [PERSON] et al. [65] selected the lightning location data in Beijing from 2007 to 2008 to calculate the distribution of lightning density, and used the geographic information system (GIS) to assess the risk of lightning disasters in Beijing. The results showed that the risk of lightning disasters in urban areas in Beijing was generally high. [PERSON] et al. [66] selected Baltimore, as a representative of large cities in the United States, to conduct detailed research on the characteristics of lightning activity in the vicinity of the city. Given the complex and diverse terrain in China, there are significant regional differences in the characteristics of lightning activity [36; 37]. Scholars have found that the Taihang Mountains in the west and the Yanshan Mountains in the north are areas with high concentrations of CG lightning, by analyzing lightning detection data [67]. The location data of lightning in Beijing from 1995 to 1997 was analyzed and it was found that lightning was mainly distributed in the east, south, southeast, north, northwest, and other directions [36]. [PERSON] et al. [68] utilized the data from the China Meteorological Administration lightning location network to delve into the temporal and spatial patterns of ground lightning activity in Beijing.