On the geomagnetic effect of the Starfish high-altitude nuclear explosion

A high-altitude nuclear explosion, called Starfish, over Johnston Island on July 9, 1962, produced a distinct geomagnetic effect at stations all over the world. This effect consisted of two major parts: initial rapid oscillations followed by slower changes. The rapid oscillations began within several seconds after the shot, and were caused by the propagation of ELF (extremely-low-frequency electromagnetic waves) and hydromagnetic waves. The slower changes reached a maximum a few minutes after the shot and lasted about half an hour. The worldwide pattern of these slow changes indicates that they were due not to a single effect but to a superposition of different effects. A quantitative estimation is made of these slow changes, taking into consideration ionospheric variations, and the results of these estimations are compared with the observed changes.