Impact of the Vertical Velocity Field on Charging Processes and Charge Separation in a Simulated Thunderstorm

A three-dimensional (3D) charging-discharging cloud resolution model was used to investigate the impact of the vertical velocity field on the charging processes and the formation of charge structure in a strong thunderstorm. The distribution and evolution of ice particle content and charges on ice particles were analyzed in different vertical velocity fields. The results show that the ice particles in the vertical velocity range from 1 to 5 m s-1 obtained the most charge through charging processes during the lifetime of the thunderstorm. The magnitude of the charges could reach 1014 nC. Before the beginning of lightning activity, the charges produced in updraft region 2 (updraft speed 13 m s-1) and updraft region 1 (updraft speed between 5 and 13 m s-1) were relatively significant. The magnitudes of charge reached 1013 nC, which clearly impacted upon the early lightning activity. The vertical velocity conditions in the quasi-steady region (updraft speed between -1 and 1 m s-1) were the most conducive for charge separation on ice particles on different scales. Accordingly, a net charge structure always appeared in the quasi-steady and adjacent regions. Based on the results, a conceptual model of ice particle charging, charge separation, and charge structure formation in the flow field was constructed. The model helps to explain observations of the lightning hole phenomenon.