Geophysical Effects of High-Altitude Nuclear Explosions

Abstract

PROMINENCE has been given recently to some geophysical effects of the nuclear tests carried out in August 1958 at Johnston Island in the Pacific. According to newspaper reports¹, these tests included high-altitude explosions at heights of the order of 100 miles on August 1 and August 12; for each date the approximate time of the explosion was 1050 U.T. Observations² at Apia, Samoa, show that the test on August 1 coincided with the appearance of an aurora and the occurrence of radio fade-outs at Apia. The special significance of these phenomena is that Apia and Johnston Island lie approximately at opposite ends of a geomagnetic line of force, and the observations at Samoa have been explained³ as due to the generation of charged particles by the test at Johnston Island and the subsequent guidance of the particles along the line of force to produce increased ionization in the lower ionosphere at Apia, the conjugate point. This mechanism would suggest that any effects are largely restricted to the vicinities of the two ends of the line of force; we wish to present evidence, however, strongly suggesting that increased D-layer ionization occurs for distances far greater from the explosion than has hitherto been realized, and at places remote from either the explosion or its geomagnetic conjugate.