Effects of Horizontal Charge Distribution in Thunderstorm Clouds on Lightning Discharge

The charge structure of thunderstorm and its internal charge distribution is an important subject in the field of atmospheric electricity research, because it has a direct impact on characteristics of lightning discharge. Influences of different charge structures in thunderstorm on lightning discharge are studied in many aspects, such as lightning types, polarity, and scales, however, but there are few quantitative investigations on effects of the horizontal distribution. Therefore, based on the existing stochastic lightning parameterization scheme, a thundercloud model is set up based upon the work of Stolzenburg et al.(1998) revealing charge structure with four charge regions within convective updrafts in thunderstorms and a negative screening layer usually exists at the top of storms. Parameters that control the horizontal distribution of charge is introduced, and then 2-dimensional fine-resolution lighting discharge simulations are performed. Results show that horizontal distribution forms of charge in upper positive region play a key role in lightning discharge, and with forms of charge changes from dense unevenness into single uniform, lightning type changes from positive cloud-to-ground flashes to positive intra-cloud flashes, then into negative cloud-to-ground flashes, and finally into positive intra-cloud flashes in limited cases. When the distribution of charge levels in the main negative charge region tends to be uniform, the type of lightning changes from negative cloud-to-ground flashes to positive intra-cloud flashes, then to positive cloud-to-ground flashes and finally to positive intra-cloud flashes in limited cases. The horizontal distribution of space charge has a significant effect on the propagation of lightning leader. If it is dense uneven, the leader propagates in the center of the charge density, otherwise, the leader can extend more than 10 to 20 km in the horizontal direction. As the horizontal distribution of charge in the charge region tends to be uniform, potential lines between two charge regions are concentrated towards the charge density center, and the potential well extends horizontally, causing the different initial potential values of the lightning trigger points, which result in the generation of different types of lightning and far-spreading lighting leader in the horizontal direction.