Mechanism for propagation of a positive leader

A model of leader breakdown in air is considered. The channel is formed due to heating of the streamer trace in the field of the streamer zone. A prev ious model of a streamer is generalized with allowance for recombination of charged particles. A mathematical model of heating of the streamer trace i s developed. It is demonstrated that, at a given potential, the ignition of the channel is provided by streamers that possess a certain charge and the corresponding propagation velocity. This velocity determines the propagati on velocity of a steady leader. The dependence of the leader velocity on th e cloud potential is found. The results obtained are compared with the data from in-situ observations and laboratory studies. (C) 2000 MAIK "Nauka/Int erperiodica".