Electric Field Pulse Trains Occurring Prior to the First Stroke in Negative Cloud-to-Ground Lightning

In this study, we examine the characteristics of electric field pulse trains that are attributed to preliminary breakdown in negative cloud-to-ground lightning discharges and compare them to those of similar pulse trains associated with attempted cloud-to-ground leaders. The data were acquired in 2006 in Gainesville, Florida. The largest pulses in the train can exceed in magnitude the following first return-stroke pulse. The arithmetic mean pulse duration and interpulse interval for pulse trains in negative cloud-to-ground discharges are 4.8 and ${65};mu$s, respectively. The arithmetic mean pulse duration and interpulse interval for pulse trains in attempted cloud-to-ground leaders are 17 and ${73};mu$s, respectively. This implies that pulse trains in ground discharges contain a larger fraction of “narrow” pulses (apparently disregarded in previous studies), defined here as those with durations equal to or less than ${4};mu$s, than the pulse trains in attempted cloud-to-ground leaders. Submicrosecond-scale pulses are observed as part of pulse trains associated with cloud-to-ground discharges, but not with attempted leaders. We also examine the occurrence of pulses of different duration and amplitude in different parts of the preliminary breakdown pulse train of ground discharges. Pulses with larger durations (${≪}hbox{4}$ $mu$s) tend to occur in the initial part of pulse train.