Relationships between kinematics, microphysics, and lightning in High Plains storms observed during the Severe Thunderstorm Electrification and Precipitation Study

The Severe Thunderstorm Electrification and Precipitation Study (STEPS) was established to improve our understanding of electrification mechanisms and lightning in High Plains storms. In particular, STEPS focused on investigating anomalous positive cloud-to-ground (CG) lightning, which had been documented to occur more often in this region than in the rest of the U.S. Radar and lightning observations of four storms observed during the STEPS field campaign are analyzed and discussed. The four cases include a predominantly positive CG-producing (PPCG) supercell on 29 June, a supercell on 3 June that produced no CG lightning of either polarity, a negative CG-producing multicellular storm on 19 June, and a PPCG multicellular storm on 22 June. The purpose of this study is to determine what features are unique for storms that produce predominantly positive CG lightning, and attempt to reveal the processes that lead to this behavior.; The results indicate that PPCG storms tend to have larger updrafts (both wider and larger in volume), which is consistent with previous studies. Large updrafts and enhanced vertical vorticity also play an important role in the production of large hail. Furthermore, low-level negative charge (below a larger region of positive charge) was observed in the cases that produced positive CG lightning, which may be the impetus needed for the flash to come to ground. This lower negative charge, in essence, represents the lowest charge layer of an inverted tripolar charge structure.{09}The charge structures observed during the production of negative CG lightning were a normal tripole (with negative charge situated between upper and lower positive charge layers) on 19 June and an inverted dipole (with negative charge above positive) in the anvil on 22 June. Cloud-to-ground flash rates (of either polarity) decreased when either the lower charge layer of the corresponding tripolar structure was absent, or when the low-level charge layer exhibited an enhanced number of LMA sources, in which case intra-cloud (IC) discharges seemed to be preferred between the two lowest charge layers of the tripole.