On the progression of sequential attempted leaders preceding a subsequent negative stroke in a bipolar lightning flash
Abstract
The present work consists of a detailed analysis of the progression of almost twenty successive attempted leaders that precede a single dart leader that reaches ground, as observed by a high-speed camera set to record 2500 frames per second. This dart leader gave rise to the first subsequent negative stroke in a bipolar flash initiated by a positive return stroke. Evidences suggest that the flash occurred in a region of inverted-polarity structure of a larger thunderstorm. The initiation processes of all the four subsequent negative strokes were clearly visible below cloud base, making it possible to track each attempted leader until the return stroke is produced. The attempted leaders began as regular recoil leaders retracing channel branches previously ionized by the positive leader that created the conductive channel of the initial positive stroke. One important aspect is that they did not clearly propagate progressively towards ground, with some of them not always reaching as far as previous attempted leaders did. Their two-dimensional speeds were estimated to be of the order of 106 m s-1, corresponding to the lower end of the distribution present in literature for both dart and recoil leaders. Approximately 166 ms after the initial positive stroke, one of the recoil leaders touched ground and initiated the first subsequent negative stroke. As far as the authors know, this is the first report of optical observations of this kind of leader behavior. Previous works present in literature have found evidences of sequential attempted leaders from VHF mapping, but this process is commonly hidden by the cloud opacity for optical instruments. The unique visibility features of the thunderstorm in which the analyzed event occurred have made it possible to obtain additional insights into this behavior present in some of the lightning flashes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMAE13B0357C
- Keywords:
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- 3324 ATMOSPHERIC PROCESSES Lightning;
- 3304 ATMOSPHERIC PROCESSES Atmospheric electricity