Positive charge region in lower part of thunderstorm and preliminar process of negative cloud to ground lightning

A new lightning locating technology, called Lightning Mapping Array (LMA), has been developed. The system takes the advantage of GPS technology to measure the times of arrival (TOA) of lightning impulsive VHF radiation events at each remote location. The temporal and 3D spatial development processes of lightning are described by measurements of the system with high time resolution (50 ns) and space precision (50-100 m). The charge structures in thunderstorms and the relationship between the charge structure and lightning discharge processes are revealed. The temporal and spatial characteristics of preliminary breakdown process in negative cloud to ground(CG) lightning discharges are analyzed based on the data of lightning VHF radiation events. The effect of the positive charge region in the lower part of thunderstorms on the occurrence of negative CG lightning discharge is discussed. The results indicate that the preliminary breakdown process with longer lasting time of negative CG lightning discharges is an intracloud discharge process between the negative and positive charge regions located in the lower and middle parts of thunderstorms respectively. It initiated from the negative charge region in the middle part and propagated downward. After entered the positive charge region in the lower part, the lightning channel developed horizontally. The characteristics of preliminary breakdown process are consistent with that of inverted intracloud lightning discharges. The stepped leaders were initiated by the K type breakdown which occurred in the last stage of the preliminary breakdown process and penetrated downward through the positive charge region. The existence of positive charge region in the lower part of thunderstorms is the reason why there is a preliminary breakdown process with longer lasting time in thunderstorms before the first return stroke of negative CG lightning discharges take place. 