Lightning in the Anvils of Supercell Thunderstorms

This study uses data from the Oklahoma Lightning Mapping Array (OK-LMA), the National Lightning Detection Network, and the Norman, Oklahoma (KOUN), prototype Weather Surveillance Radar-1988 Doppler (WSR-88D) radar to examine the evolution and structure of lightning in the anvils of supercell storms as they relate to storm dynamics and microphysics. Several supercell storms within the domain of the OK-LMA were examined to determine whether they had lightning in the anvil region, and if so, the time and location of the initiation of the anvil flashes were determined. Every warm-season supercell storm had some flashes that were initiated in or near the stronger reflectivities of the parent storm and propagated 40–70 km downstream to penetrate well into the anvil. Some supercell storms also had flashes that were initiated within the anvil itself, 40–100 km beyond the closest 30-dB Z contour of the storm. These flashes were typically initiated in one of three locations: 1) coincident with a local reflectivity maximum, 2) between the uppermost storm charge and a screening-layer charge of opposite polarity near the cloud boundary, or 3) in a region in which the anvils from two adjoining storms intersected. In some storms, anvil flashes struck ground beneath a reflectivity maximum in which reflectivity ≥20 dB Z had extended below the 0°C isotherm, possibly leading to the formation of embedded convection. This relationship may be useful for identifying regions in which there is a heightened risk for cloud-to-ground strikes beneath anvil clouds. In one storm, however, anvil lightning struck ground even though this reflectivity signature was absent.