Spread F Development associated with a High-Altitude Nuclear Explosion

Abstract

AT 0900 U.T. July 9, the American Atomic Energy Commission exploded a thermo-nuclear device of megaton yield some hundreds of kilometres in the atmosphere above Johnston Island (16.7° N., 169.4° W.). In order to observe any ionospheric phenomena which might be associated with the blast, the event was monitored at Sydney (34.05° S., 150.66° E.) by using a panoramic ionosonde previously described¹, providing ionograms made by a 15-sec linear scan over a frequency-range 0.5–9.5 Mc/s at the rate of 1 every min. Fig. 1 shows an ionogram taken immediately prior to the explosion, the blast occurring immediately at the end of this particular scan. Fig. 2 shows an ionogram taken 2 min later, the first ionogram following the explosion having been lost by equipment malfunction. It is apparent that F region frequency spreading, which before the blast covered a range of 0.2 Mc/s, had extended considerably after the event and in fact on the extraordinary ray there is evidence of spreading over a range of at least 1.5 Mc/s. At 1000 h U.T., frequency spread had decreased to 0.7 Mc/s and was still evident at 1100 h U.T.