Radar and Lightning Observations of Normal and Inverted Polarity Multicellular Storms from STEPS

This study discusses radar and lightning observations of two multicellular storms observed during the Severe Thunderstorm Electrification and Precipitation Study. The Lightning Mapping Array data indicated that the charge structure of the 19 June 2000 storm was consistent with a normal polarity tripole, while the 22 June 2000 storm exhibited an overall inverted tripolar charge structure. The 19 June storm consisted of weaker convection and produced little to no hail and moderate total flash rates peaking between 80 and 120 min−1. The cells in the 22 June 2000 storm were much more vigorous, exhibited strong, broad updrafts, and produced large quantities of hail, as well as extraordinary total flash rates as high as 500 min−1. The National Lightning Detection Network (NLDN) indicated that the 19 June storm produced mostly negative cloud-to-ground (CG) lightning, while the 22 June storm produced predominantly positive CG lightning, peaking at 10 min−1 just after two cells merged. However, the Los Alamos Sferic Array indicated that many of the positive CG strokes reported by the NLDN in the 22 June storm were intracloud discharges known as narrow bipolar events. Negative CG lightning was also observed in the 22 June storm, but typically came to ground beneath an inverted dipole in the storm anvil.