Abstract:
A small percentage of total cloud-to-ground lightning flashes lowers positive charge to ground. Storms producing positive ground flashes generally have small percentages of positive flashes. An exception can be found in many severe storms. Positive ground flashes are often clustered in time and space in and near convective regions of severe storms with a rate and density comparable to the negative ground flash rates and densities usually observed in ordinary thunderstorms. Eighty-four cases from March-August 1998 producing a majority of positive ground flashes in the convective regions of squall lines and isolated thunderstorms for a minimum of one hour have been selected for a preliminary climatology. The cases were analyzed for geographical distribution of total positive ground flashes and the number of hours with ≥50% and ≥10 total positive flashes were heavily concentrated in the central part of the United States from northern Texas to the Dakotas. This study will serve as a basis for future work in developing a climatology focusing on the relationship of positive ground flashes in convective regions of squall lines and isolating thunderstorms to the frequency of severe weather.
Paper available upon request.