The electrical processes in the intervals between the strokes of a lightning discharge

Abstract

A new electric fluxmeter has been used to record the fields of thunderclouds in the intervals between 388 strokes of 105 flashes to ground at various distances. Most of the inter-stroke interval is found to be occupied by a slow j field-change, which is negative when nearer than 5 km. and positive when further than 12 km. From this and other information from individual discharges, the j process is interpreted as one which links the positively-charged branched top of the lightning-channel successively with fresh regions of negative charge higher and higher within the cloud and so gives rise to separate strokes. Linkage is usually effected by upwardly-directed positive streamers. It is suggested that the charged regions involved in separate strokes form a single continuous column extending nearly vertically and sometimes over 6 km. in length. A mechanism is proposed to account for the intermittent discharge of this column and evidence adduced from field-change records in support of it. As some of the negatively-charged regions lie between 3⋅5 and 9⋅0 km. above ground and the freezing-level in these storms was at a height of 3⋅7 km., charge-separation must occur in the ice and snow region. Many flashes at a distance show a large, slow, final positive field-change which may be due to a discharge of positive electricity from the top of the cloud to the upper air.