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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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An Advanced Model of Lightning M‐Component
Abstract An advanced nonlinear and nonuniform distributed circuit (RLCG) model of lightning M‐component has been developed. The model accounts for the variation of the series resistanceRof M‐component channel due to its heating by the transient current and its subsequent cooling, longitudinal voltage drop along the channel due to the background continuing current, ohmic losses in the channel corona sheath (represented by shunt conductanceG), and variation of series inductanceLand shunt capacitanceCof the channel with height above ground. The model was tested against the channel‐base current and corresponding close electric fields measured for seven M‐components in negative lightning triggered using the rocket‐and‐wire technique. Detailed sensitivity analysis was performed for one M‐component. The influences of height‐varying series inductance and shunt capacitance and the length of in‐cloud channel (representing the excitation source) on the computed current and field waveforms were found to be relatively insignificant, while the influences of ohmic losses in the channel corona sheath and voltage drop along the grounded channel were significant. The effects of background continuing current level and grounding resistance were significant for M‐field, but not for M‐current. Model‐predicted overall power and current profiles below the cloud base are consistent with the observed M‐component luminosity profiles and are drastically different from the observed downward leader/upward return stroke profiles. The characteristic feature of M‐components, the time shift between the current onset and close electric field peak (essentially absent for leader/return stroke sequences), was well reproduced by our model.
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- Award ID(s):
- 1701484
- PAR ID:
- 10459913
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 124
- Issue:
- 4
- ISSN:
- 2169-897X
- Page Range / eLocation ID:
- p. 2296-2317
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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