Signatures of large peak current lightning strokes during an unusually intense sprite-producing thunderstorm in southern England

During the night of 26–27 May 2017, a mesoscale convective system (MCS) rapidly developed over Cornwall and Devon in the South West of England, producing about 3500 lightning flashes in 3 h and 23 sprites. The MCS-type storm was characterised by a circular shape with a size of about 52,000 km² (cloud top temperature lower than - 40 °C) and a local minimum in the CG flash rate (~15 min⁻¹), when most of the sprites were observed. The mean intensity of the sprite parent CG strokes was exceptionally high in this case (+170 kA), while the associated charge moment changes ranged from 600 to 2000C km. Two identical detectors, located at different sites in southern England, measured the quasi-static displacement currents induced on metallic electrodes when exposed to the changing atmospheric electric field produced by the storm's discharges. A series of coincident large amplitude short-peak transients, some of which associated with the sprite-producing strokes, were recorded on these detectors. A multi-instrumental analysis of the lightning events producing transient current “spikes” on the electrodes revealed a significant bias towards large peak currents exceeding 100 kA, but only a minor dependence on the impulse charge moment change (iCMC) for those associated with the sprites. We suggest that the current spikes may be induced by a coupling with the electromagnetic impulse radiated by intense lightning discharges. The ease in discriminating such signatures makes the method suitable for monitoring the occurrence of powerful lightning, potentially associated with night-time transient luminous events (TLEs), thereby avoiding the limitations inherent to optical observations and radio noise affecting other receivers.