Very Close High-Speed Photographic Observations of a Natural Negative Cloud-To-Ground Lightning Stepped Leader
Abstract
High-speed photographic studies of laboratory negative stepped leaders in air present highly detailed pictures of the stepwise forward propagation of laboratory-scale leaders. Because of the difficulties inherent in obtaining high-speed imaging of natural lightning, especially first strokes, there are relatively few if any comparable high-speed photographic observations of negative stepped leaders in natural lightning. Normal photographic and video observations of natural lightning negative stepped leaders show structural similarities to laboratory negative stepped leaders that are strongly suggestive of common processes. However, because of the electrodeless environment and much larger scale of natural lightning, it is possible that the apparently similar processes may differ in significant ways. To address this uncertainty, we present a sequence of contrast-adjusted frames of a descending natural negative stepped leader obtained with a Photron SA1 at 10,000 frames/sec. These frames show multiple occurrences of short bipolar discharge segments forming just ahead of the tips of branches of a natural descending negative stepped leader. The segments appear to have a structure that is similar to that of a laboratory space leader where a short ionized conducting channel segment is capped on one or both ends by brighter streamer zones just ahead of the main negative leader channel. The faint luminosity of the segments relative to the main leader channel suggests that the segments are electrically floating and lack strong discharge currents, while the relative brightening at the extremities of the segments suggests corona or streamer discharge activity. These segments appear to be physically identical to the step-forming bipolar space leader segments that have been observed in laboratory studies.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMAE11A..04B
- Keywords:
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- 3304 ATMOSPHERIC PROCESSES / Atmospheric electricity;
- 3324 ATMOSPHERIC PROCESSES / Lightning