Cloud-to-ground lightning in linear MCS archetypes without trailing stratiform precipitation

As documented by Parker and Johnson (1999), there exist three distinct archetypes for midlatitude linear mesoscale convective systems (MCSs): those comprising convective lines with trailing stratiform precipitation (TS), leading stratiform precipitation (LS), and parallel stratiform precipitation (PS). In recent years, the arrangement and frequency of cloud-to-ground (CG) lightning in TS MCSs has received a great deal of study. However, linear MCSs with leading or parallel stratiform precipitation have received comparatively little attention. The authors will document the typical arrangement and frequency of CG lightning, as well as departures therefrom, for four LS and four PS MCSs that occurred during May 1996 and May 1997. This study of CG lightning in distinctly non-TS MCSs can shed light on previous results concerning TS case studies and populations, as well as contribute to the presently scant literature on the LS and PS archetypes.

On average, the LS cases had relatively low flash densities, but were similar to previously studied TS MCSs in that they produced both a convective mode of positive CG lightning (+CG) early in their lifetimes and a stratiform mode of +CG late in their lifetimes. In comparison to previously published results, the LS MCSs in the present study may represent significant producers of +CG. Conversely, although the PS systems had higher average flash densities than the LS systems, they did not exhibit prolonged convective +CG modes, and they produced a lower overall fraction of +CG. 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 within their stratiform precipitation regions.

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Parker, M.D., and R.H. Johnson, 1999: On the organization of midlatitude mesoscale convective systems. Preprints, Eighth Conference on Mesoscale Processes, 28 June-1 July 1999, Boulder, CO, 8-13.