Properties of Trains of Strong Preliminary Breakdown Pulses Which Are Followed by Weak Return Stroke

Abstract:

We analyze characteristics of trains of very strong preliminary breakdown pulses (PBPs). The amplitudes of the largest PBPs exceed more than four times the amplitudes of the following return strokes or non-return stroke like pulses. This could indicate an abnormally electrified storm and a high occurrence of attempted cloud-to-ground leaders.

We measure waveforms of the magnetic-field derivative using a broad-band analyzer with a sampling interval of 12.5 ns coupled with a newly designed magnetic-loop antenna. The analyzed frequency band goes from 5 kHz to 37 MHz. We use numerically integrated waveform records for the analysis of the properties of the trains.

Our dataset consists of 11 trains of magnetic-field preliminary breakdown pulses measured during one single thunderstorm, which occurred close to Rustrel, France in June 2013 and lasted about four hours. All observed trains of PBPs were followed by very week return strokes or non-return stroke like pulses. The lightning detection networks METEORAGE and EUCLID classified 10 of 11 trains of strong PBPs as a negative cloud-to-ground discharge (1), positive cloud-to-ground discharges (3) or intra-cloud discharges (6). The corresponding return strokes were absent in the list provided by lightning detection networks (7) or classified as negative cloud-to-ground (2) or intra-cloud discharges (2). The discharges were located at distances between 69 and 176 km from the receiving site.

We estimate the duration, the number of pulses and the inter-pulse intervals for each individual train. We also estimate the time between the last pulse in the train and the peak of the following return stroke or non-return stroke like pulse. We investigate the variability in the pulse shapes and the differences between the observed trains and the regular trains of PBPs preceding usual negative cloud-to-ground flashes.