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- Title
Insights Into Lightning K‐Leader Initiation and Development From Three Dimensional Broadband Interferometric Observations.
- Authors
Jensen, Daniel P.; Shao, Xuan‐Min; Sonnenfeld, Richard G.
- Abstract
We report detailed observations of K‐leaders and the activity between them with the three‐dimensional Broadband Interferometric Mapping and Polarization system (BIMAP‐3D) at Los Alamos National Laboratory. It is found that K‐leaders have a general propagation trend of initial acceleration and then gradual deceleration, and the corresponding very high frequency (VHF) radiation power is exponentially correlated with the leader speed. Based on the 3D development and simultaneous electric field change measurement, some simple K‐leaders can be modeled with time‐evolving point charges at the propagating leader tip and at the stationary origin. We found that the charge magnitude increases during the initial acceleration stage and stays relatively constant for the rest of the development. K‐leaders are observed to interact with other branches; the branches affect the leader's propagation speed, and may affect the charge transfer. After the occurrence of a K‐leader, VHF emissions are quenched for several milliseconds. VHF sources then reappear in an impulsive and scattered manner as "twinkling," and these sources are found not uniquely on the so‐called needles, but also on the main channel. These twinkling sources start near the apparent positive leader tip, and extend back toward the direction of the flash origin at about 105 m/s, while the apparent positive tip continues to extend forward at about 104 m/s. The twinkling extending toward the direction of flash origin appears to initiate the following K‐leader, although it may be interrupted by a K‐leader along a different branch, or simply die out without more K‐leader activity. Plain Language Summary: A K‐leader is a discharge process that occurs at the later stage of a lightning flash. It retraces the path established by earlier discharges and propagates at a high speed of 106–107 m/s. Recently we developed a new system called BIMAP‐3D that can map lightning radio sources in 3D at a spatial resolution of 10 m and at a time resolution of a fraction of a microsecond. We found that K‐leaders commonly speed up from 106 to 107 m/s at the initial stage and then gradually slow down to a stop at their later stage, with associated radio power positively correlated with the traveling speed. Other branches in the lightning flash are found to affect the K‐leader speed as it approaches and passes the branch junctions due to charge redistribution caused by the earlier processes. After the occurrence of a K‐leader radio emissions are shut off for a few milliseconds due to the increased conductivity of the leader. After that, scattered radio sources reappear in an expanding region, both extending the branch and expanding back toward the starting point of the lightning. These apparent twinkling radio sources lead to the start of the next K‐leader. Key Points: K‐leader propagation often exhibits an initial acceleration followed by a gradual decelerationK‐leaders often sharply decelerate and then sharply re‐accelerate as they approach and pass branch junctions in the flash structureA bidirectionally extending region of "twinkling" very high frequency sources leads to the initiation of the next K‐leader
- Subjects
LOS Alamos National Laboratory; ELECTRIC field strength; SPATIAL resolution; THUNDERSTORMS
- Publication
Journal of Geophysical Research. Atmospheres, 2023, Vol 128, Issue 23, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2023JD039104