Very Low-Frequency Radiation from Lightning Strokes

A theory of the generation of low-frequency electromagnetic radiation by cloud-ground lightning strokes is presented. Only the effect of the return stroke is considered. The predicted form of the radiated pulse from the return stroke is a single cycle with a field variation which varies linearly with time. The spectral distribution of the radiated energy is found to be centered at about 11 kc, with a total width at half-maximum of 12 kc. The total energy radiated in one leader and return stroke is estimated at 220,000 joules. Some qualitative considerations on the emission of radiation at extremely low frequencies are given.