Corona envelopes and lightning currents

Laboratory results on coronas and considerations of fundamental electrostatics are used to study the corona envelope around the lightning channel. Calculations predict that immediately after a return stroke, a corona current of the order 2 kA flows for less than a millisecond, that between steps of a stepped leader corona draws a current of about 3 kA, and that at all other times the current governed by the velocity of radial charge motion is less than 1 A. Observed currents in all phases of the lightning discharge are accounted for by longitudinal channel extension, not radial expansion. A speculative picture of the roles of the corona envelope and of channel extension in discrete strokes of lightning is presented.