Time and space correlation between sprites and their parent lightning flashes for a thunderstorm observed during the HyMeX campaign

During the night of 22–23 October 2012, together with the Hydrology cycle in the Mediterranean eXperiment (HyMeX) Special Observation Period 1 campaign, optical observations of sprite events were performed above a leading stratiform Mesoscale Convective System in southeastern France. The total lightning activity of the storm was monitored in three dimensions with the HyMeX Lightning Mapping Array. Broadband Extremely Low Frequency/Very Low Frequency records and radar observations allowed characterizing the flashes and the regions of the cloud where they propagated. Twelve sprite events occurred over the stratiform region, during the last third of the lightning activity period, and well after the coldest satellite-based cloud top temperature (−62°C) and the maximum total lightning flash rate (11 min−1). The sprite-producing positive cloud-to-ground (SP + CG) strokes exhibit peak current from 14 to 247 kA, Charge Moment Changes (CMC) from 625 to 3086 C km, and Impulsive CMC (iCMC) between 242 and 1525 C km. The +CG flashes that do not trigger sprites are initiated outside the main convective core, have much lower CMC values, and in average, shorter durations, lower peak currents, and shorter distances of propagation. The CMC appears to be the best sprite predictor. The delay between the parent stroke and the sprite allows classifying the events as short delayed ( 20 ms). All long-delayed sprites, i.e., most of the time carrot sprites, are produced by SP + CG strokes with low iCMC values. All SP + CG flashes initiate close to the convective core and generate leaders in opposite directions. Negative leaders finally propagate toward lower altitudes, within the stratiform region that coincides with the projected location of the sprite elements.