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Abstract High‐speed video records of a single‐stroke positive cloud‐to‐ground (+CG) flash were used to examine the evolution of eight needles developing more or less radially from the +CG channel. All these eight needles occurred during the later return‐stroke stage and the following continuing current stage. Six needles, after their initial extension from the lateral surface of the parent channel core, elongated via bidirectional recoil events, which are responsible for flickering, and two of them evolved into negative stepped leaders. For the latter two, the mean extension speed decreased from 5.3 × 106to 3.4 × 105and then to 1.3 × 105 m/s during the initial, recoil‐event, and stepping stages, respectively. The initial needle extension ranged from 70 to 320 m (N = 8), extension via recoil events from 50 to 210 m (N = 6), and extension via stepping from 810 to 1,870 m (N = 2). Compared with needles developing from leader channels, the different behavior of needle flickering, the longer length, the faster extension speed, and the higher flickering rate observed in this work may be attributed to a considerably higher current (rate of charge supply) during the return‐stroke and early continuing‐current stages of +CG flashes.
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High‐Speed Video Observations of Needles in a Positive Cloud‐to‐Ground Lightning Flash
Abstract High‐speed video data were used to analyze the initiation and propagation of 36 needles and their associated 306 flickering events observed in a single‐stroke positive cloud‐to‐ground (+CG) flash. The needles occurred during the return‐stroke later stage and the continuing current, within approximate 10 ms after the onset of the +CG return stroke. They initiated near the lateral surface of the predominantly horizontal channel and extended almost perpendicular to that channel. Flickering events are recoil type streamers (or leaders) that retrace the channels created by needles. Flickering events can be repetitive and are classified into four categories based on different scenarios of their occurrence. Needles are caused by the radial motion of negative charge from the hot core of the positive‐leader channel into the positive corona sheath surrounding the core, when the core is rapidly recharged (its radial electric field reversed) by the return‐stroke process and during the following continuing current.
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- Award ID(s):
- 2114471
- PAR ID:
- 10363026
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 2
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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