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In this study 29 initial breakdown pulses (IBPs) from four intracloud (IC) lightning flashes are modeled using data from five or more electric field change (E-change) sites. For each flash the first 5–9 located IBPs are investigated. For each IBP the modeling first extracts the IBP current waveform from the E-change data by matrix inversion and then determines the best channel length and current velocity to match the IBP data. Derived IBP quantities of total charge, charge moment, peak current, peak radiated power, and total energy are calculated. Resulting IBP vertical lengths varied from 27 m to 1300 m; most values were 100–500 m. Current velocities ranged over 4.0–20.0 × 107 m/s, with most values 10–16.5 × 107 m/s. Two of these IC flashes had two “extraordinary” IBPs each with very large E-change amplitude and multiple subpulses; these four extraordinary IBPs had longer current rise times than fall times and charge moments of −3.45 to −20.06C km. Subpulses of classic IBPs were coincident with, and likely caused by, smaller current pulses superimposed on the main IBP current. Overall, most of the 29 IC IBPs had peak current amplitudes <120 kA and total (negative) charge <2C, while the four extraordinary IB pulses had peak currents of 217–359 kA and total charges of −8.4C to −71.7C. The four extraordinary IBPs all have the characteristics of Energetic In-cloud Pulses (EIPs), which are thought to be the radio signals of events producing terrestrial gamma-ray flashes (TGFs). The extraordinary IBPs may have caused double-pulse TGFs and overlapping TGFs.

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Available for download on Sunday, October 15, 2023