Observations of narrow bipolar events reveal how lightning is initiated in thunderstorms

Abstract

A long-standing but fundamental question in lightning studies concerns how lightning is initiated inside storms, given the absence of physical conductors. The issue has revolved around the question of whether the discharges are initiated solely by conventional dielectric breakdown or involve relativistic runaway electron processes. Here we report observations of a relatively unknown type of discharge, called fast positive breakdown, that is the cause of high-power discharges known as narrow bipolar events. The breakdown is found to have a wide range of strengths and is the initiating event of numerous lightning discharges. It appears to be purely dielectric in nature and to consist of a system of positive streamers in a locally intense electric field region. It initiates negative breakdown at the starting location of the streamers, which leads to the ensuing flash. The observations show that many or possibly all lightning flashes are initiated by fast positive breakdown.

Spontaneous Emergence of Space Stems Ahead of Negative Leaders in Lightning and Long Sparks

“…Our results thus stress the role in maintaining the corona played by poorly understood processes such as the inception of counterpropagating streamers Luque et al, 2016) or the propagation of successive ionization waves along preexisting channels (Babich et al, 2015;Nijdam et al, 2014;Phelps, 1974;Rison et al, 2016). However, at around 100 ns, the overall conductivity of a streamer channel decays, stalling 10.1029/2019GL082063 the increase in temperature.…”

Observations of the initial stage of a rocket‐and‐wire‐triggered lightning discharge

“…It consisted of three broadband VHF discone antennas placed at the vertices of an equilateral triangle 20 m on each side. The processing code is the same as that developed for the lightning initiation study by Rison et al [2016] and is based upon the analysis techniques of Stock et al [2014]. For this study, the data segments were 128 samples (0.64 μs) in length, and successive segments were displaced 32 samples (0.16 μs) relative to the preceding segment.…”

VHF and UHF Electromagnetic Radiation Produced by Streamers in Lightning

“…The decay rate of the current moment is assumed to be three times of that of streamer deceleration, just as the growth rate of current moment (e.g., ∼ 1.7×10 9 s −1 for case I) being three times of streamer acceleration (e.g., ∼ 6×10 8 s −1 for case I; Shi et al, 2016). We further assume the transition between growth and decay occurs when the propagating streamer reaches the maximum speed ∼ 5 × 10 7 m/s observed for sprite streamers (e.g., Liu et al, 2015;McHarg et al, 2007) or narrow bipolar events (e.g., Rison et al, 2016). We further assume the transition between growth and decay occurs when the propagating streamer reaches the maximum speed ∼ 5 × 10 7 m/s observed for sprite streamers (e.g., Liu et al, 2015;McHarg et al, 2007) or narrow bipolar events (e.g., Rison et al, 2016).…”