Cloud-to-Ground Lightning in Linear Mesoscale Convective Systems

Recently, three distinct archetypes for midlatitude linear mesoscale convective systems (MCSs) have been identified: those comprising convective lines with trailing stratiform precipitation (TS), leading stratiform precipitation (LS), and parallel stratiform precipitation (PS). While cloud-to-ground (CG) lightning in TS MCSs has received a great deal of study in recent years, linear MCSs exhibiting leading or parallel stratiform precipitation have received comparatively little attention. This paper documents the arrangement and frequency of CG lightning for four LS and four PS MCSs that occurred during May 1996 and May 1997. On average, the LS cases bore some similarity to previously studied TS MCSs; they produced predominantly positive CG lightning (1CG) early in their lifetimes (concomitant with convective precipitation) and late in their lifetimes (concomitant with stratiform precipitation). In contrast with previously published results for MCSs in general, the LS MCSs in the present study overall had relatively low negative CG (2CG) flash densities, yielding higher percentages of 1CGs than other MCS archetypes. While the PS systems had higher average flash densities than the LS systems, they did not exhibit prolonged 1CG modes early in their lifetimes, and they produced a lower overall fraction of 1CGs. Notably, the presence of line-parallel flow may render a somewhat unique electrical character in PS systems. In particular, the PS MCSs in this study exhibited enhanced CG lightning in the vicinity of decaying convective cells that were embedded within their stratiform precipitation regions.