Lightning location relative to storm structure in a leading‐line, trailing‐stratiform mesoscale convective system

Horizontal and line‐normal, vertical cross‐sections and composite images of Dallas‐Fort Worth Lightning Detection and Ranging (LDAR II) VHF radiation sources and radar reflectivity over a 30‐min period provide a unique perspective on lightning pathways within a leading‐line, trailing‐stratiform (LLTS) mesoscale convective system (MCS) on 16 June 2002. The overwhelming majority of VHF lightning sources occurred within the leading convective line in a bimodal pattern in the vertical. Assuming that VHF source density maxima were most likely associated with positive charge, then the LDAR II observations suggest that the gross charge structure of the convective region of the MCS was characterized by a tripole with net positive charge centered at 4.5 km AGL (3°C) and 9.5 km AGL (−35°C) and net negative charge centered roughly in the relative minimum of the VHF source density maximum at 7 km AGL (−17°C). A persistent lightning pathway and inferred positive charge zone sloped rearward (by 40–50 km) and downward (by 4–5 km) from the upper VHF source maximum in the convective line, through the transition zone, and into the radar bright band of the stratiform region. In the stratiform region, VHF lightning sources and inferred positive charge were concentrated in three layers centered at 4.5, 6, and 9 km AGL (2°C, −11°C, and −31°C, respectively), consistent with past electric field studies of symmetric LLTS MCSs. Positive cloud‐to‐ground lightning flashes in the stratiform region were initiated in the convective line and followed the slanting pathway from the top of convective cores to the stratiform precipitation, where they were horizontally extensive, layered, and highly branched. The sloping lightning pathway was identical to hypothetical trajectories taken by snow particles. These observations provide further support for the advection of charge on snow along the sloping pathway and the in situ generation of charge in the horizontal lightning layers as primary contributors to electrification and positive lightning production rearward of the convective line.