Locating Preliminary Breakdown Pulses in Positive Cloud‐to‐Ground Lightning

Abstract

This paper provides the first concrete evidence that preliminary breakdown (PB) pulses of either polarity in positive cloud-to-ground (+CG) lightning are produced by negative leaders. Three-dimensional location results of PB pulses in 46 +CG flashes are analyzed. The majority (40) of the +CG flashes started with positive PB pulses (+PBPs), the same polarity as the positive return stroke. Location results showed that +PBPs were produced by leaders propagating upward, which were determined to be negative leaders based on PB pulse polarities. Similarly, for the negative PB pulses (ÀPBPs) found in six +CG flashes, location results showed that they were produced by leaders propagating downward, and we determined that these were also negative leaders. Upward negative leaders producing +PBPs in +CG lightning are very similar to those in intracloud lightning. They usually propagate upward before turning in a horizontal direction. Downward negative leaders producing ÀPBPs in +CG lightning are more complicated. They usually move back upward after a period of downward propagation. Positive leaders could not be detected, but their possible propagations are analyzed along with possible charge structures for different types of PB pulses. We also demonstrate that PB pulse studies based on single-site records are potentially unreliable.Plain Language Summary Lightning flashes usually start with a train of bipolar pulses called preliminary breakdown (PB) pulses. In negative cloud-to-ground (ÀCG) flashes, PB pulses usually have negative initial polarity, the same as the negative return stroke. However, in +CG flashes, PB pulses with either polarity have been observed by many studies. PB pulses in +CG flashes are usually explained by the movement of positive leaders because a positive leader connecting the ground is always necessary for a +CG flash. In this study, we provide the first concrete evidence that PB pulses of both polarities are produced by negative leaders. Specifically, positive PB pulses are produced by upward-propagating negative leaders and negative PB pulses are produced by downward-propagating negative leaders. Possible charge structures for different types of PB pulses in +CG flashes are also discussed.

Velocities of Positive Leaders in Intracloud and Negative Cloud‐to‐Ground Lightning Flashes

“…As evidence for the discussion (section ), overall velocities of downward positive leaders in +CG flashes are also briefly analyzed. As reported by Wu et al (), 46 +CG flashes were observed inside or near the network of the FALMA during the summer of 2017. Positive leader velocities were roughly estimated by dividing the 3‐D distance by the time difference between the first source of a flash and the first return stroke.…”

Origin of an Uncommon Multiple‐Stroke Positive Cloud‐to‐Ground Lightning Flash With Different Terminations

“…On one hand, VHF lightning mapping array location results show that many +CGs terminate below the stratiform region but originate from the convective area of the thunderstorm (Lang et al, 2004;Lu et al, 2009;van der Velde et al, 2014). On the other hand, the +CG flashed that started with a PB process as reported by Wu et al (2018) tend to have a rather small horizontal distance (less than 5 km, estimated from the figures) from the initiation location.…”

“…They speculated that the PB acts as a downward positive leader from the upper positive charge region. By mapping 46 +CGs preceded by a PB pulse train, Wu et al (2018) considered that the PB of either polarity is produced by the propagation of negative leaders rather than the propagation of positive leaders. They further suggested that all +CGs seem to start with a PB, which is sometimes weak, and that the initial lightning leader develops bidirectionally between a large positive charge region and a small negative charge region below.…”

Characterization of Multitermination CG Flashes Using a 3D Lightning Mapping System (FALMA)

“…The time-of-arrival technique was applied for locating the pulses on the electric field change (E-change) waveforms (obtained with the 12 fast antennas). As shown in Reference [10], using FALMA, we could do 3D mapping for all lightning occurring inside a network, and the estimated horizontal location accuracy for locating return strokes (RSs) was around 20 m. So far, the data obtained by FALMA in 2017 have been used for several scientific studies [11][12][13]. To characterize the 205 MTFs, we chose the following seven parameters, with four (parameters 1-4) of them having previously been used by other authors and the remaining three (parameters 5-7) being counted for the first time in this study.…”