Modeling the development of the stepped leader of a lightning discharge

A stochastic-deterministic model is presented for the propagation of a down ward-moving leader. Lightning formation is described by a stochastic growth of branching discharge channels which is determined by the electrostatic f ield. The dynamics of the electric field and of the charge distribution ove r the lightning structure are calculated deterministically. The model inclu des the initiation of lightning, a preliminary discharge in a cloud, the pr opagation of a downward-moving stepped leader toward the earth, and the ini tiation and upward motion of a return stroke from the earth's surface. Nume rical execution of the model yields a dynamic picture of the development of the downward-moving leader and of the intracloud discharge structure. The effect of the charge density in the cloud and the parameters of the develop ing channels on the spatial-temporal, current, and charge characteristics o f the stepped leader's propagation are studied. The effect of free-standing structures on the distribution of points on the earth's surface where ligh tning strikes is examined. (C) 1999 American Institute of Physics. [S1063-7 842(99)00904-6].