Broadband Characteristics of Chaotic Pulse Trains Associated With Sequential Dart Leaders in a Rocket‐Triggered Lightning Flash

Abstract

Based on simultaneous measurements of fast E‐field change, very high frequency radiation and channel mapping, channel base current, and high‐speed video, the characteristics of chaotic pulse trains (CPTs) during propagation of dart leaders in a rocket‐triggered lightning were analyzed. The triggered lightning involved 16 subsequent leader‐return strokes traversing in the same grounding channel. At least five dart leaders showed significant CPT signals during its propagation, with much larger intensity than that in normal leader stage at broadband of low‐frequency–medium‐frequency, very high frequency, and visible light band. All CPTs occurred in the final stage of the leader development, within 150 μs prior to the return strokes. The leader velocity and the charge transfer are both related to the instantaneous intensity of CPT, but the relationship is not always solid when the two parameters are considered individually. Nevertheless, the large product of return stroke charge to 1 ms and the velocity of the leader (QV) could be a reliable proxy/indicator for CPT. All CPTs correspond to a larger local QV with a threshold higher than 1 × 107 C · m/s when CPT is determined as chaotic electric field pulses with magnitude larger than 3 std of the magnitude of E‐fluctuation waveform of the whole flash.

Fine Structure of the Breakthrough Phase of the Attachment Process in a Natural Lightning Flash

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The attachment process in cloud-to-ground lightning flashes is a crucial process that eventually switch on the discharge route between the cloud and the ground, acting as a transition from the leader stage with a peak current of 1-2 kA to the return stroke stage with a peak current of several tens of kiloamperes (Pu et al, 2019;Rakov & Tran, 2019). In response to the downward leaders starting from the charged clouds, upward connecting leaders (UCLs) of the opposite polarity are initiated from the grounded objects, extend their channels toward the approaching downward leader and make contact, followed by the collision and return stroke (Saba et al, 2017).

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Activation of Abundant Recoil Leaders and Their Promotion Effect on the Negative‐End Breakdown in an Intracloud Lightning Flash

“…However, the frequent occurrence of recoil leaders was after a strong process that quickly developed through the in‐cloud conducting channel, stuck out of the cloud, and reached the multiple channel extremities. Generally, the chaotic impulsive EM characteristic is related to the leader breakdown process in negative polarity (Pu et al., 2019), considering a bidirectional concept of the lightning development, the positive current wave that lighted up the images maybe the opposite‐end effect due to the in‐cloud breakdown. Its arrival to the positive leader extremity resulted in a transition of the leader propagation from the quiet phase to the active phase producing a lot of recoil leaders.…”

A Rocket‐Triggered Lightning Flash Containing Negative‐Positive‐Negative Current Polarity Reversal During Its Initial Stage

“…The upper limits of the measurable current were 2 and 40 kA, respectively. The minimum distinguishable current of the former shunt was about 9.3 A (Pu et al., 2019; Qie et al., 2017).…”