On the role of transient currents in the global electric circuit

Abstract

This study examines the way in which different types of lightning, both cloud-to-ground (CG) and intracloud (IC) flashes, drive current in the global circuit. A numerical model of the transient electric field due to CG and IC flashes and their Maxwell relaxation (slow transients) is developed. The electric field (E) and current distributions, the decay time of E, and the total charge transferred to the ionosphere and the ground are calculated. Because of the slow transients, only a portion of the charge neutralized by a flash contributes to the global circuit, with the efficiency depending on the altitudes of the lightning charges. Typical CG flashes have efficiencies of 55-75%, and typical IC flashes have 5-15%. An example from balloon E data has been used to verify the theory. Total current estimations of the combined CG and IC slow transient processes in the global electric circuit range from 50-400 A. Copyright 2008 by the American Geophysical Union.