Vertical Radar Reflectivity Structure and Cloud-to-Ground Lightning in the Stratiform Region of MCSs: Further Evidence for In Situ Charging in the Stratiform Region

Abstract

This study presents further evidence in support of an in situ, noninductive charging mechanism as the process likely responsible for significant electrification of the trailing stratiform regions of mesoscale convective systems (MCSs). In contrast to previous studies of MCS electrification that have investigated observations of radar reflectivity and cloud-to-ground lightning in the horizontal (e.g., Orville et al.; Rutledge et al.), here the relationship between the location and occurrence of cloud-to-ground lightning in the stratiform regions of midlatitude and tropical MCSs and the vertical profile of radar reflectivity are examined. The vertical profile of radar reflectivity at elevations above the 0°C level is used as a proxy for the amount of mass present in the mixed-phase region of the stratiform clouds, which in turn is related to the generation of charge through a noninductive charging mechanism. To further explore the relationship between radar reflectivity, mixed-phase microphysics, and in situ charging by means of a noninductive mechanism, we present calculations with a simple one-dimensional model used to diagnose the presence of supercooled liquid water between the 0° and ?20°C levels in the stratiform region. We use the model to contrast two cases: 1) a case in which reflectivities greater than 15 dBZ existed above the 0°C level in the stratiform clouds, cloud-to-ground lightning occurred, and moderate amounts of supercooled liquid water were present in the stratiform region (as inferred from the model results); 2) a case where no lightning was observed in the stratiform region, reflectivities above the 0°C level were less than 15 dBZ, and very little supercooled water was present (as inferred from the model results). Based on observations in several MCSs, we show that the number of cloud-to-ground lightning flashes in the stratiform region is highly correlated with the vertical radar reflectivity profile.