A subsequent positive stroke developing in the channel of preceding negative stroke and containing bipolar continuing current

Abstract

A bipolar cloud-to-ground lightning flash was observed to exhibit two types of polarity reversal associated with the first two strokes separated by a not unduly long time interval of 70 ms. The first stroke was negative and had a peak current of −101 kA. The second stroke was positive, had a peak current of 16 kA and was followed by a 122 ms long bipolar continuing current. The first two strokes, including the bipolar continuing current, occurred in the same channel to ground, whose imaged 2-D length was 4.2 km. The occurrence of positive stroke in the negative-stroke channel is highly unusual. The 2-D speed versus height profiles for the negative stepped leader of the first stroke and, for the first time, for the positive leader in the previously conditioned, first-stroke channel were examined and the average speeds were found to be 4.7 × 105 m/s and 7.2 × 105 m/s, respectively.