Simulation of Various Connecting Patterns During the Lightning Connection Process Based on the Stochastic Lightning Leader Model

Considering the observed fact that most upward connecting leaders (UCL) does not branch during downward negative cloud-to-ground (CG) strikes, the simulation scheme of upward positive leaders is modified based on the existing two-dimensional (2D) stochastic lightning model. In addition, two connecting patterns, i.e., the tip-to-tip connecting and the tip-to-lateral connecting (lateral strike) between the downward leader and the UCL are simulated during the process in which lightning strikes tall buildings. Sensitivity experiments are carried out on the connecting process between leaders during the process of lightning striking a tall building by altering the horizontal distance between the initiation point of the downward leader (at a height of 1000 m) and the tall building. Results indicate that when the value of d increases from 0 to 700 m, the probability of a lateral strike for the UCL generally exhibits a trend of first increasing and then decreasing. As the value of d increases, the length of the UCL exhibits an increasing trend, and the ratio of the part of the UCL above the connecting point accounting for the entire length of the UCL upon the lateral strike generally exhibits an increasing trend. The probability of each grounding position is under the influence of the horizontal distance. The UCL initiating from the top of tall structures is longer than that initiating from the ground or the side surface of tall structures. Furthermore, tall structures with different heights are also investigated.