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Imaging Step Formation in In-cloud Lightning Initial Development with VHF Interferometry
  • Yunjiao Pu,
  • Steven A. Cummer
Yunjiao Pu
Duke University
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Steven A. Cummer
Duke University

Corresponding Author:[email protected]

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We investigate sequential processes underlying the initial development of in-cloud lightning flashes in the form of initial breakdown pulses (IBPs) between 7.4–9.0 km altitudes, using a 30–250 MHz VHF interferometer. When resolved, IBPs exhibit typical stepped leader features but are notably extensive (>500 meters) and infrequent (~1 millisecond intervals). Particularly, VHF radio features indicating space stems and space leaders are identified, evidencing the conducting main leader forming. We observed five distinct phases within an IBP stepping cycle: the emergence of space stems with discrete VHF pulses at previous streamer zone edges, the conversion to a space leader, the fast VHF propagation along the space leader, an immediate transition to fast breakdown into undisturbed air, and a decaying corona fan. These measurements illustrate clearly the processes involved in the initial development of in-cloud lightning flashes and provide insights into other processes known to occur simultaneously, such as TGFs.
26 Sep 2023Submitted to ESS Open Archive
30 Sep 2023Published in ESS Open Archive