A unified engineering model of the first stroke in downward negative lightning

Abstract

Each stroke in a negative cloud-to-ground lightning flash is composed of downward leader and upward return stroke processes, which are usually modeled individually. The first stroke leader is stepped and starts with preliminary breakdown (PB) which is often viewed as a separate process. We present the first unified engineering model for computing the electric field produced by a sequence of PB, stepped leader, and return stroke processes, serving to transport negative charge to ground. We assume that a negatively charged channel extends downward in a stepped fashion during both the PB and leader stages. Each step involves a current wave that propagates upward along the newly formed channel section. Once the leader attaches to ground, an upward propagating return stroke neutralizes the charge deposited along the channel. Model-predicted electric fields are in reasonably good agreement with simultaneous measurements at both near (hundreds of meters, electrostatic field component is dominant) and far (tens of kilometers, radiation field component is dominant) distances from the lightning channel. Relations between the features of computed electric field waveforms and model input parameters are examined. It appears that peak currents associated with PB pulses are similar to return stroke peak currents, and the observed variation of electric radiation field peaks produced by leader steps at different heights above ground is influenced by the ground corona space charge.

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

“…In most previous IBP modeling studies (e.g., da Silva & Pasko, ; Karunarathne et al, ; Kašpar et al, ; Nag & Rakov, ; Nag & Rakov, ; Shao & Heavner, ), IBPs have been modeled using smooth IBP current waveforms that produce smooth bipolar pulses without any of the subpulses commonly detected on the leading side of the waveform (e. g., Weidman & Krider, ; Stolzenburg et al, ). To be able to include subpulses, we determine the IBP current waveform I ( t ) from the IBP E‐change measurements.…”

Initial breakdown and fast leaders in lightning discharges producing long‐lasting disturbances of the lower ionosphere

“…Among all lightning flashes, IB pulses were rarely observed in VLF (with >8 dB SNR) at distances greater than a few hundred kilometers, as will be discussed in the next section. Based on this criterion, we have classified the IB radiation reported in this paper (observed at distances greater than a few hundred kilometers) as “intense.” Recent experimental and modeling studies indicate that peak currents producing IB pulses may be as large as several tens of kiloamps [ Karunarathne et al , ; da Silva and Pasko , ; Kolmašová et al , ], flowing over channels with lengths on the order of a few hundred meters to a kilometer [ Stolzenburg et al , , ; Karunarathne et al , ; da Silva and Pasko , ; Nag and Rakov , ]. Such large currents have been demonstrated to produce initial breakdown observable at a distance of 600 km [ Kolmašová et al , , ].…”

“…For detailed information regarding the physical nature of IB, we refer the reader to the recent experimental works of Campos and Saba [2013], Stolzenburg et al [2013Stolzenburg et al [ , 2014, and Wilkes et al [2016]. Recent efforts in modeling currents in initial breakdown processes include the works of Karunarathne et al [2014], da Silva and Pasko [2015], and Nag and Rakov [2016].…”

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

“…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.…”