Near-ground detection of atmospheric γ rays associated with lightning

Abstract

Data taken at 6–20 m above ground from March through June of 2002 was used to confirm that the background subtracted atmospheric γ radiation (GRR) was directly related to precipitation rates. An anomalous increase in GRR (AGR) shortly after lightning strokes several times that expected from only the observed precipitation was concurrently observed at two sites separated by a distance of 220 m. The increase in activity in the detector environment subsequently decayed with a half-life of about 50 min. A model, which assumes the presence of an ensemble of radioisotopes produced by proton and photon-induced nuclear reactions in the atmosphere, fits the observed 50 min (33 min) decay half-life without (with) rain with correlation coefficients of 0.98. The possibilities that energetic protons and to a lesser extent brehmsstrahlung resulting from ions accelerated in electric fields during positive lightning produce this delayed activity and that AGR may be used as a remote monitor of lightning as well as the relative intensity of integrated lightning activity are discussed herein.