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Abstract Using visible‐range and infrared (3–5 μm) high‐speed video cameras, we observed luminosity transients that reilluminated decayed branches of two close (2 to 4 km) negative stepped leaders in Florida. Leader branches were energized via stepping at their tips and, as a result, were most heated near their lower ends, with the hotter sections being connected via cooler sections to the trunk. In the modeling of lightning leaders, usually a single tip is considered. In contrast, in the present study, many (up to 30 per major branch) tips were active at the same time, forming a network‐like structure with a descending multitip “ionization front” whose transverse dimensions were of the order of hundreds of meters. The front exhibited alternating stepping, with each step necessarily generating a positive charge wave traveling from the leader tip up along the channel, like a mini return stroke. We inferred that the step‐related waves can cause luminosity transients in the remnants of decayed negative branches at higher altitudes. Such reactivated branches, in turn, may facilitate further leader stepping at lower altitudes, as first reported by Stolzenburg et al. (2015,https://doi.org/10.1002/2014JD022933). The reactivation process is likely to involve multiple steps, as evidenced by a large number of active tips (some tens per 50‐μs frame) and corresponding electric field pulses occurring at time intervals of 2 μs or less. Additionally, our observations suggest that a transient in one decayed branch can trigger (or assist with triggering of) a transient in another branch.
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Evidence and Inferred Mechanism of Collisions of Downward Stepped‐Leader Branches in Negative Lightning
Abstract Using visible‐range and infrared (3–5 µm) high‐speed video cameras, we observed collisions of adjacent branches in downward negative stepped leaders. Typically, a lagging (chasing) branch (CB) approached a leading branch (LB) from aside at about 90° angle and connected to the lateral surface of the LB within some tens of meters or less of its tip. We infer that collisions can be facilitated by the attracting force of upward moving positive‐charge wave associated with stepping at the leading branch tip. Outcomes of branch collisions differ. The chasing branch may be absorbed by the LB, rebound, or temporarily bridge two branches. It appears that a heavily branched negative stepped leader creates a highly structured and rapidly changing electric field pattern inside the volume it occupies. We observed abrupt changes in the direction of branch extension, suggesting that the direction of local electric field can differ significantly from the ambient.
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- Award ID(s):
- 1701484
- PAR ID:
- 10446494
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 48
- Issue:
- 11
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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