Characteristics of a rocket‐triggered lightning flash with large stroke number and the associated leader propagation

Abstract

A negative lightning flash with 16 leader-return stroke sequences, triggered in the summer of 2013 using the classical rocket-and-wire triggering technique, was examined with simultaneous two-dimensional (2D) imaging of very high-frequency (VHF) radiation sources, channel-base current measurement, broadband electric field waveforms and high-speed video images. A total of 28.0 C negative charge was transferred to ground during the whole flash, and the charge transferred during the initial stage was 4.9 C, which is the weakest among the triggered lightning flashes at the SHandong Artificially Triggering Lightning Experiment (SHATLE). The peak current of 16 return strokes ranged from 5.8 to 32.5 kA with a geometric mean of 14.1 kA. The progression of upward positive leader and downward negative (dart or dart-stepped) leaders was reproduced visually by using an improved short-baseline VHF lightning location system with continuous data recording capability. The upward positive leader was mapped immediately from the tip of the metal wire during the initial stage, developing at a speed of about 10 4 m/s without branches. The upward positive leader and all the 14 negative leaders captured by the 2D imaging system propagated along the same channel with few branches inside the cloud, which might be the reason for the relatively small charge transfer. The 2D imaging results also show that dart leaders may transform into dart-stepped leaders after a long time interval between successive strokes.

Features of Upward Positive Leaders Initiated From Towers in Natural Cloud‐to‐Ground Lightning Based on Simultaneous High‐Speed Videos, Measured Currents, and Electric Fields

“…The results are compatible with those presented by Yokoyama et al () and Gao et al () for negative CG lightning. It is interesting to note that the estimated two‐dimensional speeds are still similar to those reported for positive leaders of negative upward lightning, 0.081 × 10 6 m/s according to Wang et al (), and of negative rocket triggered lightning, 0.038 × 10 6 m/s to 0.21 × 10 6 m/s in the works by Sun et al () and Biagi et al (), respectively.…”

“…In three other events, the pulses observed in the measured current were correlated with the pulses of the close electric field. Sun et al () identified VHF sources at the tip of a propagating upward positive leader in a sole negative triggered lightning and also observed pulses of current in the initial continuous current. Though no correlation was observed between the pulses of current and VHF radiation, they presumed a stepwise propagation of the positive leader.…”

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

“…The signals from each antenna were bandpass filtered to 25-90 MHz and recorded with 16 bit resolution at a sampling rate of 200 MHz continuously for 2 s. The recorded time series waveforms were postprocessed utilizing generalized cross-correlation time delay algorithm [Sun et al, 2013[Sun et al, , 2014Stock et al, 2014], applied to sequences of overlapping data segments from the time series waveforms. It consisted of three broadband VHF discone antennas placed at the vertices of an equilateral triangle 20 m on each side.…”

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

“…The last gray panel shows the overlapped locations of all radiation sources of F1302. Detailed propagating characteristics of each leader have been discussed in Sun et al (). Here we show them again to facilitate our understanding of what happened inside the cloud when CPT occurred.…”

“…The channel base current, VHF radiation and channel mapping, fast E‐field, and high‐speed video images in this study were obtained during a classical rocket‐triggered cloud‐to‐ground lightning flash F1302 in SHAndong Triggering Lightning Experiment (SHATLE). The flash F1302 was triggered at 21:37:12 UT on 2 August 2013 and had a large return stroke number of 16 (Lu et al, ; Sun et al, ). The satellite image of the SHATLE is shown in Figure .…”