Long-lived effects in theDregion after the high-altitude nuclear explosion of July 9, 1962

Abstract

Papers have recently been published describing the behavior of the phase of VLF signals propagating over long VLF paths after the high‐altitude nuclear explosion of July 9, 1962 [Burtt, 1962; Zmuda et al., 1963]. These papers have been concerned with the effects within a few minutes of the explosion. In this note we intend to show that effects were also produced which lasted for at least one week. On July 9, 1962, at around 0900 UT, the event known as Starfish took place. This was the detonation of a 1.4‐MT nuclear weapon at a height of 400 km [Zmuda et al., 1963] over Johnson Island in the Pacific. Figure 1 shows the diurnal phase variation [Chilton et al., 1963] of the signals at 19.8 kc/s from NPM in the Hawaiian Islands received at Boulder during the month of July 1962. The initial effect of the explosion on this path, near 0900 UT on July 9, resulted in the phase of the signal approaching or possibly passing its daytime value, although the path was in complete darkness at this time. Almost immediately afterward the phase began to return to normal and was still recovering when the eastern end of the path became sunlit. During the days following, the figure shows that the diurnal variation was much reduced, and it was not until July 17 that the diurnal phase change returned to the value it had before the event.

Schumann resonances

“…There are VLF observations [Zmuda et aI, 1963] that can be explained by a lower· ing (or increasing electron density) of the D-region boundary. Brady et al , [1964] interpreted VLF di· urnal phase shifts to show that some enhanced D· region ionization persists for several days following the event.…”