Production of terrestrial gamma-ray flashes by an electromagnetic pulse from a lightning return stroke

Recent observations of terrestrial gamma-ray flashes (TGFs) ( Smith et al., 2005) suggest the need for a new mechanism of TGF production. Consideration of relativistic runaway electron (RRE) avalanche driven by electromagnetic impulses (EMP) radiated by rapidly moving lightning return strokes indicates that TGFs can be produced by discharges with peak return stroke currents I-p > 450 - 700 kA with velocities v(rs)/c = 0.99 - 0.995.