Luminosity of initial breakdown in lightning

Abstract

[1] Time correlated high-speed video and electromagnetic data for 15 cloud-to-ground and intracloud lightning flashes reveal bursts of light, bright enough to be seen through intervening cloud, during the initial breakdown (IB) stage and within the first 3 ms after flash initiation. Each sudden increase in luminosity is coincident with a CG type (12 cases) or an IC type (3 cases) IB pulse in fast electric field change records. The E-change data for 217 flashes indicate that all CG and IC flashes have IB pulses. The luminosity bursts of 14 negative CG flashes occur 11-340 ms before the first return stroke, at altitudes of 4-8 km, and at 4-41 km range from the camera. In seven cases, linear segments visibly advance away from the first light burst for 55-200 ms, then the entire length dims, then the luminosity sequence repeats along the same path. These visible initial leaders or streamers lengthen intermittently to about 300-1500 m. Their estimated 2-D speeds are 4-18 Â 10 5 m s À1 over the first few hundred microseconds and decrease by about 50% over the first 2 ms. In other cases, only a bright spot or a broad area of diffuse light, presumably scattered by intervening cloud, is visible. The bright area grows larger over 20-60 ms before the luminosity fades in about 100 ms, then this sequence may repeat several times. In several flashes, a 1-2 ms period of little or no luminosity and small E-change is observed following the IB stage prior to stepped leader development.

Modeling initial breakdown pulses of CG lightning flashes

“…In several CG flashes, typical downward negative stepped leader developed (after a delay and dark interval of several milliseconds) from near the lower end of the initial leader. Stolzenburg et al [2013a] also showed that each luminosity burst was time correlated with a large-amplitude IBP, whose duration was typically 20-40 μs. Marshall et al [2013] used the array of E-change sensors described in Karunarathne et al [2013] and PBFA locations to study IBPs in IC flashes.…”

“…Both Stolzenburg et al [2013a] and Karunarathne et al [2013] found that the initial negative leader of CG flashes moves negative charge downward.…”

“…Our goal is to determine some of the physical parameters of the IBPs. As described briefly above, Stolzenburg et al [2013a] provided detailed comparisons of video data to E-change data of the negative initial leader in several CG flashes. In data having a 20μs frame rate and 19.6μs image exposure, Stolzenburg et al [2013a] found the following sequence of luminosity and E-change events in each downward extension of the initial leader:…”

“…Watson and Marshall [2007] introduced MTLEI with exponentially increasing current to model narrow bipolar pulses. The video data of Stolzenburg et al [2013a] indicate that the current in IBPs decreases with distance traveled from the new extension back along the previous luminous path, so we choose the MTLL and MTLE models from previous studies. According to high-speed video images presented in Stolzenburg et al [2013a], it appears that the brightest point of the initial leader occurs just above the bottom of the channel.…”

A Study of Preliminary Breakdown and Return Stroke Processes in High-Intensity Negative Lightning Discharges

“…Rakov and Uman [3] stated that the PB process can be viewed as a sequence of channels extending in seemingly random directions from the cloud charge source with one of them evolving into the stepped leader propagating to ground. More recent studies of preliminary breakdown by Stolzenburg et al [4,5], who used high-speed video and electric field records, indicated that the PB luminosity bursts were correlated with the PB pulses in the corresponding electric field records and suggested that each PB pulse was caused by a substantial current surge traversing a channel segment of the order of hundreds of meters in length. Nag and Rakov [6], via modeling, estimated the PB pulse peak currents to be of the order of tens of kiloamperes, comparable to or even exceeding the corresponding return-stroke peak current.…”