Lightning charge moment changes in U. S. High Plains thunderstorms

We report measurements of impulsive (2 ms) lightning charge moment changes in more than 1000 cloud-to-ground (CG) return strokes detected by the National Lightning Detection Network in three United States High Plains storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) field program of 2000. The positive CG strokes (+CGs) in a mesoscale convective system exhibit an unusual charge moment distribution with a small median and long tail. Analysis suggests the presence of two different classes of +CGs in this MCS, one with small charge moment changes (less than or equal to50 C km) and the other containing larger charge moment changes (50-1400 C km). The distributions of negative cloud-to-ground stroke charge moment changes are roughly log-normal in shape with means varying from 17.7 to 36.8 C km. When combined with past measurements these means vary by a factor of 4 between storms, and there is probably not a single distribution that represents well all storms.