The Climatology of Meteorological Conditions Favorable for the Production of Large Impulse Charge Moment Changes

Warm-season mesoscale convective systems (MCSs) are hypothesized to be associated with the production of large (>100 C km) impulse charge moment change (iCMC) cloud-to-ground discharges. Large positive iCMC lightning has been associated with the occurrence of sprites. These discharges often occur in precipitation systems featuring a line of convection either leading or trailing a region of stratiform precipitation with a spatially large positive charge layer for positive parent lightning strokes to tap. Large negative iCMC discharges are far less common, but are occasionally observed in warm-season MCSs. The definition of "large iCMC" varies with whether or not a mesospheric sprite is produced by the parent lightning stroke, e.g. a positive iCMC value of 300 C km or larger has a 75-80% chance to produce a sprite (Lyons et. al. 2009). The threshold of 100 C km as a lower cutoff for large iCMCs is used here. Meteorological regimes differing from the "normal" warm-season MCS mode have been found to produce large iCMCs as well. A climatology of precipitation systems that produce large iCMC discharges is presented. Case studies are also used to characterize the meteorological conditions supporting the production of large iCMC discharges, both positive and negative. Future research includes the use of the total charge moment change (CMC) versus the iCMC parameter as well as a characterization of smaller thresholds of iCMC values.