Progressive lightning. VII Directly-correlated photographic and electrical studies of lightning from near thunderstorms

Abstract

An analysis has been made of the direct correlation of luminous and electrical field-changes produced by thirty-seven lightning discharges to ground. These discharges comprised 199 separate strokes, most of which were within a distance of 6 km. A new form of drum camera and a camera shutter operated by the first leader were employed, and many records were obtained in daylight. When compared with results previously reported for flashes at distances of 10 km. or more, the following major differences are found: negative field-changes from near leaders, absence of electrical effects of first leader steps and hook-shaped field-changes during the period immediately following the return stroke. The hook field-changes are shown to be associated with components in the continuing luminosity of the channel of the type investigated by Malan & Collens and to be due to subsidiary discharges in this channel. These 'M' components carry negative charge to ground in quantities between one-fifth and one-hundredth of those carried by main strokes. The height of the lower negative charge in these thunderclouds is found to be from 4 to 9 km. During a discharge to ground, no rapid discharges occur within the cloud or elsewhere than in the cloud-ground channel. A fairly slow discharge of the upper positive charge in the thundercloud appears to occur to the upper air immediately after the lower negative pole has discharged to ground.