Effect of a High-Altitude Nuclear Detonation on the Earth-Ionosphere Cavity

The spectrum of ELF radio noise around the fundamental resonant frequency (about 8 cps) of the earth-ionosphere cavity was analyzed for the period including the time of detonation of a large nuclear device in the ionosphere over Johnston Island. The peak-power frequency of the first mode was found to drop abruptly by about 1/2 cps at the time of the burst. The time required for recovery of the cavity from the disturbed condition appeared to be of the order of 3 or 4 hours.