Ratio of leader to return stroke electric field change for first and subsequent lightning strokes

Abstract

The ratio of leader to return stroke electric field change versus distance is presented as a function of stroke order for 218 first and subsequent strokes in 70 cloud‐to‐ground flashes which occurred near Tampa, Florida, in 1979. The measured leader to return stroke field ratio tended to be more negative as the stroke order increased, implying that the charge sources for successive strokes were, on average, progressively farther from both the observer and the ground strike point. Sixteen percent of all flashes analyzed contained at least one leader‐return stroke sequence with a negative net electric field change; that is, a ratio that is less than −1. These strokes were observed at distances from 2.5 to 11.6 km, with 56% farther than 8 km. They exhibited a strong tendency to occur late in a flash, with 89% occurring after the fourth stroke. The geometic mean initial electric field peak normalized to 100 km for strokes with a ratio less than −1 was found to be 1.1 V/m, 2.6 times lower than for all subsequent strokes in our data base.