High-speed photographs of lightning at close range

Abstract

Time sequences of lightning photographs were taken at a range of about 100 meters, covering fields of about 10 by 15 meters. Film frames were exposed for 2 μ sec at intervals of about 100 μsec. Analysis of these records has yielded accurate determination of the lightning channel diameter, changes in brightness with time, and changes in the geometry of the channel within individual return strokes and from stroke to stroke within a single flash. Three films successfully exposed show that the diameter of the stroke is typically from 30 to 120 mm, that the stroke brightness usually decreases monotonically from a time within 50 μsec of its onset (but may fluctuate in brightness in some cases). Within a single stroke the shape of the channel ordinarily remains constant, but changes do occur from stroke to stroke within a single flash.