Positive cloud to ground lightning return strokes

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Abstract
Several recent papers have reported positive cloud‐to‐ground lightning, but, in our opinion, none provides sufficiently direct evidence that positive return strokes occurred in any given case. Here we present observations that plainly demonstrate the occurrence of positive return strokes in a convective thunderstorm in Florida in August 1982. These observations consist of waveforms of electric field correlated in time with light pulses received through a narrow collimated slit aimed about 1.2 degrees above a level plane and with videotape records of lightning channels. We studied lightning during one 15‐min interval at a range of 20–40 km. During this period we recorded time‐correlated waveforms from three positive return strokes. The 10–90% rise times of the electric fields, 1–5 μs, and of the light pulses, 3–6 μs, were similar to those of negative return strokes in the same storm. The light signals of the positive return strokes began 2–8 μs after the electric fields, consistent with return‐stroke speeds of about 108 m s−1, a value comparable to speeds of ordinary negative return strokes.

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