Characteristics of Preliminary Breakdown Pulses in Positive Ground Flashes during Summer Thunderstorms in Sweden

Abstract

This paper presents the characteristics of the preliminary breakdown pulses (PBP) in 51 positive ground flashes recorded during 2014 summer thunderstorms in Sweden. Electric field measurements were conducted remotely using a broadband antenna system (up to 100 MHz) for a recording length of 1 s with 200 ms trigger time. In the analysis, PBP trains were observed in 86% of the cases. Based on the number of trains preceding the first return stroke, the PBP were classified into single and multiple train PBP. Characteristics of the first PBP train were determined and based on the initial polarity of the pulses, three types of PBP were identified. Characteristics of the subsequent PBP trains in the multiple train PBP were also analyzed and they were compared with the first PBP train. Based on the conceptual charge cloud configuration, we found that the inverted dipole is consistent with our observation. We also found that PBP in positive ground flashes during summer thunderstorms in Sweden are weak since the average ratios of the PBP peak to the first return stroke peak lie only between 0.21 and 0.26. Possible reasons for no detection of PBP and the different types of PBP observed were also discussed.

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

“…It is worth noting that from about 20 ms in Figures c and d, a train of positive pulses were recorded, which were produced by the negative leader propagating upward. This explains reports of PB pulses exhibiting both polarities in the literature (Gomes & Cooray, ; Johari et al, ; Zhang et al, ). It also demonstrates that this type of PB pulse results from a negative leader that first propagates downward and then propagates upward.…”

“…On wideband electric field change (E‐change) waveforms, lightning flashes usually start with a series of bipolar pulses called preliminary breakdown (PB) pulses or initial breakdown pulses. Numerous studies have been devoted to the analysis of PB pulse characteristics (Johari et al, , and references therein). With the development of low‐frequency (LF) lightning locating systems, PB pulses in both negative cloud‐to‐ground (−CG) lightning and intracloud (IC) lightning have been located in three dimensions (3‐D), and it is now very clear that PB pulses in −CG lightning and IC lightning are usually produced by negative leaders going downward and upward, respectively, from a negative charge region (Bitzer et al, ; Karunarathne et al, ; Wu et al, ).…”

“…Many studies have found that PB pulses in +CG lightning are much more complicated than those in −CG lightning. While the initial polarity of PB pulses in −CG lightning is usually negative (using the physics sign convention), the same as the negative return stroke, the initial polarity of PB pulses in +CG lightning can be either positive or negative (Gomes & Cooray, ; Johari et al, ; Nag & Rakov, ; Qie et al, ; Schumann et al, ; Ushio et al, ; Wu et al, ; Zhang et al, ). To further complicate this problem, some studies reported observations of PB pulses with no clear polarity (Gomes & Cooray, ; Qie et al, ) and multiple pulse trains with opposite polarities (Gomes & Cooray, ; Johari et al, ; Zhang et al, ).…”

O bserved Electric Field Changes o f Positive Lightning Flashes Preceded b y Preliminary Breakdown i n Padang

“…It is still a mystery how to explain the occurrence of PBP trains in positive CGs. We speculate that in type C, there are different charge configurations in different regions of the PB pulse process [9,17,20] and the leader channel is not in vertical propagation [22,23] and has many branches in the cloud, so that there is more than one PB pulse train prior to the RS, as shown in Figure 4. …”

Comparing the Wave Characteristics of Breakdown Pulses of the Lightning Waveforms in the Himalayan Region

“…The values for both interpulse interval and total pulse duration of positive lightning were half of those of negative lightning flash [ 6 ]. The PB pulses amplitude is about 21 to 26 percent of the first return stroke in the summer thunderstorm in Sweden [ 15 ]. The preliminary breakdown pulses are seen for all types of flashes, either cloud to cloud or cloud to ground at higher latitudes, but it is not observed at lower latitudes.…”