Studying Sequences of Initial Breakdown Pulses in Cloud‐to‐Ground Lightning Flashes

Abstract

The properties of the first 5–12 classic initial breakdown pulses (IBPs) of three cloud‐to‐ground (CG) lightning flashes were determined using a modified transmission line model. As part of the modeling, the current with respect to time of each IBP was determined from the measured electric field changes at multiple sites using three theoretical methods called Hilbert transform, Hertzian dipole, and matrix inversion. In the transmission line modeling the length of each IBP was estimated from high‐speed video data of the IBPs. The modeling provided the following properties of the larger classic IBPs in each flash: peak current, velocity, total charge, charge moment, radiated power, and total energy dissipated for successive IB pulses in three developing lightning flashes. For the main initial leader channel in the three CG flashes (and for one long branch), IBP peak current was largest for the first or second classic IBP and declined mostly monotonically with successive IBPs. For the same channels, IBP current velocity was smallest for the first classic IBP and increased mostly monotonically with successive IBPs. The smallest velocities were (2.0, 2.5, 2.5, 3.0) × 107 m/s, respectively, while the largest velocities were (9.2, 12.2, 11.5, 12.0) × 107 m/s, respectively. These data support earlier hypotheses that it is the classic IB pulses during initial leader of normal negative CG flashes that change the nonconductive air into an ionized path that is sufficiently long and conductive to start the stepped leader.

Two Propagation Scenarios of Isolated Breakdown Lightning Processes in Failed Negative Cloud‐to‐Ground Flashes

“…Typical in-cloud currents, which generated the strongest isolated breakdown pulses, are similar for both types. These currents are reported by Météorage around 20 kA, and they do not differ 10.1029/2020GL090593 from peak currents, which emitted the most intense PB pulses preceding -CG discharges in Florida, USA (Karunarathne et al, 2020). Typical initiation altitudes (3.5 km, similar for both types) correspond to the region between the main negative and lower positive charge centers, where -CG discharges are initiated .…”

The Mechanism of the Origin and Development of Lightning From Initiating Event to Initial Breakdown Pulses (v.2)

“…Stolzenburg et al (2014) hypothesized that the initial leader (the IBPs) heat the initial leader channel with each successive IBP and that this heating eventually causes the initial leader to transition to a stepped leader with a hot, conducting channel. Recently, Karunarathne et al (2020) presented model results for sequences of IBPs that support this hypothesis. Plasma networks may also be developing in other cells of the EE volume, distant from the first IBPs, and they may also contribute to the series of IBPs.…”

“…i4. Classic IBPs have range-normalized (to 100 km) amplitudes averaging about 1 V/m (Smith et al, 2018) and estimated peak currents of 1-165 kA (Betz et al, 2008;Karunarathne et al, 2014Karunarathne et al, , 2020. High-speed video cameras reveal that there is a bright burst of light with each classic IBP (Campos & Saba, 2013;Stolzenburg et al, 2013Stolzenburg et al, , 2014.…”

“…The important data supporting the conclusions of this paper are included in the main text. More detailed data are available through Andreev et al 2014; Karunarathne et al (2014Karunarathne et al ( , 2015Karunarathne et al ( , 2020; Kolmasova et al (2019); Kostinskiy et al (2015aKostinskiy et al ( , 2015bKostinskiy et al ( , 2018; ; Marshall, Schulz, et al (2014); Marshall et al (2019); and Stolzenburg et al (2013Stolzenburg et al ( , 2014.…”

“…The physical process causing an IEC is unknown, but apparently, the effect is to separate and accumulate enough charge to cause the first classic IBP. Classic IBPs have range‐normalized (to 100 km) amplitudes averaging about 1 V/m (Smith et al, 2018) and estimated peak currents of 1–165 kA (Betz et al, 2008; Karunarathne et al, 2014, 2020). High‐speed video cameras reveal that there is a bright burst of light with each classic IBP (Campos & Saba, 2013; Stolzenburg et al, 2013, 2014).…”