Stroke multiplicity and horizontal scale of negative charge regions in thunderclouds

Abstract

AbstractAn X‐band polarimetric radar and multiple lightning detection systems are used to document the initial cloud‐to‐ground lightning flash in a large number (46 cases) of incipient thunderstorms, as part of the CHUVA‐Vale field campaign during the 2011/2012 spring‐summer in southeast Brazil. The results show an exceptionally low stroke multiplicity (87% of flashes with single stroke) in the initial ground flashes, a finding consistent with the limited space available for the positive leader extension into new regions of negative space charge in compact cells. The results here are contrasted with the behavior of ground flashes in mesoscale thunderstorms in previous studies. Additionally, we found evidence for a minimum scale (radar echo >20 dBZ) for lightning initiation (>3 km in radius) and that the peak currents of initial cloud‐to‐ground flashes in these compact thunderstorms are only half as large as return stroke peak currents in general.