Peak Currents and Propagation Velocities of Initial Breakdown Pulses in Cloud-to-Ground Lightning Flashes

Abstract:

Initial breakdown (IB) pulses occur at the beginning of lightning flashes. S. Karunarathne et al. [JGR-D, 2013] used modified transmission line models to determine the current risetime, current falltime, current shape factor, current propagation speed, and total charge moment change of individual IB pulses. In this presentation we show model results for series of the first 5 - 7 IB pulses in three separate CG flashes. The current with respect to time of each IB pulse is determined from the measured electric field change (E-change) and its complex conjugate at 4 – 6 sensor sites. The risetimes ranged from 10 to 50 microseconds and the falltimes were 15 to 70 microseconds; the falltime was always longer than the risetime. We used the transmission line model of Uman et al. [Am. J. Phys., 1975] for E-change deduced from Maxwell's equations along with the length of each IB pulse estimated from high-speed video data, and the above mentioned current shape to model IB pulses and calculate peak current as well as velocity. This poster describes how peak currents and current propagation velocities change for successive IB pulses in three developing lightning flashes. Initial breakdown (IB) pulses occur at the beginning of lightning flashes. S. Karunarathne et al. [JGR-D, 2013] used modified transmission line models to determine the current risetime, current falltime, current shape factor, current propagation speed, and total charge moment change of individual IB pulses. In this presentation we show model results for series of the first 5 - 7 IB pulses in three separate CG flashes. The current with respect to time of each IB pulse is determined from the measured electric field change (E-change) and its complex conjugate at 4 – 6 sensor sites. The risetimes ranged from 10 to 50 microseconds and the falltimes were 15 to 70 microseconds; the falltime was always longer than the risetime. We used the transmission line model of Uman et al. [Am. J. Phys., 1975] for E-change deduced from Maxwell's equations along with the length of each IB pulse estimated from high-speed video data, and the above mentioned current shape to model IB pulses and calculate peak current as well as velocity. This poster describes how peak currents and current propagation velocities change for successive IB pulses in three developing lightning flashes.