Luminosity in the initial breakdown stage of cloud‐to‐ground and intracloud lightning

Abstract

AbstractWe present simultaneously measured luminosity and electric field data from the initial breakdown (IB) stage in seven cloud‐to‐ground (CG) and eight intracloud (IC) lightning discharges along with, in three cases, radar and Lightning Mapping Array (LMA) data. The data were taken in north‐central Florida in 2013 and 2014. Seven CG discharges had an arithmetic mean (standard deviation, SD) IB stage luminosity pulse train duration of 3 ms (2 ms), and within the seven CG discharges, 30 luminosity pulses had the following means (SD): 10% to 90% risetime 25 µs (16 µs), full width at half maximum 68 µs (21 µs), and delay between onset of the electric field pulse and associated luminosity pulse 8 µs (8 µs). Eight IC discharges had a mean (SD) IB stage luminosity pulse train duration of 11 ms (4 ms), and within the 8 IC discharges, 37 luminosity pulses exhibited mean risetimes, widths, and delays of 59 µs (36 µs), 176 µs (70 µs), and 34 µs (20 µs), all significantly greater than in the CG case. The roughly 10 LMA sources associated with each of the three IB stages in 2014 are grouped horizontally within about 1 km2. The mean altitude (SD) of the LMA points during two CG IB stages is 5 km (600 m) and 4.3 km (250 m) and during one IC discharge is 6.2 km (550 m). We discuss the role of optical scattering in delaying and distorting the observed luminosity waveforms.