## 7 Influence of Tall Structures on Atmospheric Electrical Activity  
Modern cities are increasingly dotted with towering structures, which not only attract nearby downward CG flashes, but also initiate upward CG flashes at their summits, influencing lightning discharge characteristics. Since the 1930s, various research teams across the globe have installed optical, electromagnetic, or current detection equipment  
Figure 10: Characteristics of lightning activity in high-density building areas (**a**), characteristics of lightning activity in low-density building areas (**b**) [28]. on or adjacent to prominent high-rise structures, such as the Empire State Building in the United States, Canada's National Tower (CN Tower), the Ostankino TV Tower in Russia, the Santis Tower in Switzerland, the iron tower in Mt. San Salvatore, the Meteorological Tower in Beijing, China, and the Guangzhou Tower in China. These locations have facilitated observations and research on lightning strikes to high buildings [105; 106; 107; 108; 109; 110; 111; 112]. During the passage of a thunderstorm cloud overhead, the local electric field at the tips or corners of tall buildings is enhanced, making them more susceptible to lightning strikes, while the probability of lightning strikes to surrounding low-rise buildings or flat surfaces decreases relatively. [PERSON] and [PERSON] [113] proposed a method to calculate the flash-to-ground distance based on the characteristics of negative polarity long-gap discharges and established the electrical geometric model, which led to the development of the rolling ball method for analyzing the shielding performance of buildings. However, the rolling ball method's criteria are not applicable to taller buildings, whose height exceeds the radius of the rolling ball [114]. Some scholars have evaluated the impact of tall buildings on nearby CG flash activity by analyzing the CG flash densities around them. [PERSON] [115] used CG flash localization data to analyze the lightning activity around two iron towers in South Africa, which were 250 m and 220 m tall and separated by a distance of 5.2 km. The study found that the lightning density within a 2.5 km radius of the towers was higher than that in the annular region between 2.5 km and 10 km, suggesting that the towers have an attraction effect on lightning. With a total height of 600 m, Guangzhou Tower is the tallest tower in China. [PERSON] et al. [116] compared the location of the lightning return stroke within 1 km of the Guangzhou Tower before and after its completion, concluding that the number of CG flashes around the Guangzhou Tower increased significantly after its completion (Figure 11). The process of initiating and developing the upward leader is a key factor influencing the location of lightning strike points. Therefore, research on this process is crucial for understanding the physical processes of lightning and disaster prevention [117]. However, in natural lightning, the upward leader is usually triggered when the downward leader approaches the ground. The luminous intensity and electromagnetic radiation of the upward leader are weaker than that of the downward leader, making optical observation and radiation source localization difficult. As a result, it is currently challenging to directly detect the upward leader in natural lightning. With its controllable location, predictable occurrence time, and the ability to measure the current, the artificial triggering lightning experiment has become a vital tool for studying natural lightning. The initial phase of this experiment, where the upward leader is initiated and the initial continuous current is generated, parallels the process seen in lightning strikes triggered by tall buildings [51; 52]. Prior research has shown that when the experimental rocket reaches a height of several hundred meters, a breakdown at the top of the conductor produces an upward leader. The upward leader in artificial lightning is self-triggered and develops upward from the ground.