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Abstract Our basic knowledge of downward positive lightning leaders is incomplete due to their rarity and limited ability of VHF mapping systems to image positive streamers. Here, using high‐speed optical records and wideband electric field and magnetic field derivative signatures, we examine in detail the development of a descending positive leader, which extended intermittently via alternating branching at altitudes of 4.2 to 1.9 km and involved luminosity transients separated by millisecond‐scale quiet intervals. We show that the transients (a) are mostly initiated in previously created but already decayed branches, at a distance of the order of 100 m above the branch lower extremity, (b) extend bidirectionally with negative charge moving up, (c) establish a temporary (1 ms or so) steady‐current connection to the negative part of the overall bidirectional leader tree, and (d) exhibit brightening accompanied by new breakdowns at the positive leader end. One of the transients unexpectedly resulted in a negative cloud‐to‐ground discharge. Both positive and negative ends of the transients extended at speeds of 106–107 m/s, while the overall positive leader extension speed was as low as 103–104 m/s. Wideband electric field signatures of the transients were similar to K‐changes, with their millisecond‐ and microsecond‐scale features being associated with the steady current and new breakdowns, respectively. For transients with both ends visible in our optical records, charge transfers and average currents were estimated to be typically a few hundreds of millicoulombs and some hundreds of amperes, respectively.
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Dart‐Leader and K‐Leader Velocity From Initiation Site to Termination Time‐Resolved With 3D Interferometry
Abstract Simultaneous data from two interferometers separated by 16 km and synchronized within 100 ns were collected for a thunderstorm near Langmuir Lab on October 23, 2018. Analysis via triangulation followed by a least squares fit to time of arrival across all six antennae produced a three‐dimensional interferometer (3DINTF) data set. Simultaneous Lightning Mapping Array data enabled an independent calculation of 3DINTF accuracy, yielding a median location uncertainty of 200 m. This is the most accurate verified result to date for a two‐station interferometer. The 3D data allowed profiling the velocity of multiple dart leaders and K leaders that followed the same channel. 3D velocities calculated from the in‐cloud initiation site to ground ranged from 3 × 106to 20 × 106 m/s. Average velocity generally increased with subsequent leaders, consistent with increased conditioning of the channel. Also, all leaders showed a factor of 2–3 decrease in velocity as they proceeded over 15 km of channel. We speculate that the velocity decrease is consistent with energy lost in the reionization of the channel at the leader tip. This paper includes an appendix providing details of the triangulation technique used.
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- PAR ID:
- 10448064
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 126
- Issue:
- 9
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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