Magnetic disturbances due to the high-altitude nuclear explosion of July 9, 1962

Abstract

As part of a program of measurements of the geomagnetic field being conducted by personnel at the U.S. Naval Air Development Center (geographic coordinates 40.2°N, 75.1°W), observations were made with a rubidium vapor magnetometer during the five high-altitude nuclear detonations exploded by the United States over Johnston Island (geographic coordinates 16.5°N, 169.5°W) in 1962 for all events announced by Agiwarn messages. Of the five detonations we monitored on July 9, October 20, October 26, November 1, and November 4, 1962, the only identifiable fluctuation in the geomagnetic field observed at this location occurred after the event of July 9, 1962, when a 1.4-megaton device was detonated at an altitude of 400 km at 09h 00m 09.029s UT. For this event Baker and Strome [1962], Unterberger and Byerly [1962], Breiner [1963], Crook et al. [1963], and Wilson and Sugiura [1963] have reported on magnetograms obtained with a rubidium vapor magnetometer, and Fraser [1962], Ashburn et al. [1962], and van Wijk [1962] have discussed results obtained with other magnetometers. The rubidium vapor magnetometer in operation for this event was a Varian Associates model X4934, measuring the magnitude of the total field at a sensitivity of 2 γ full scale and at a chart speed of 2 in./min. The sensitivity of the magnetometer was such that fluctuations of the geomagnetic field greater in amplitude than 0.05 γ and having periods longer than 4 sec would be observable. The time referred to WWV is estimated to be in error by less than 1 sec. The frequency response of this magnetometer is essentially flat from O cps to about 0.25 cps, above which the recorder response begins to fall off rapidly. During the event of July 9, 1962, a second, independent magnetometer system was in operation. This system, designated AN/ASQ-10, has a saturable core magnetometer continuously stabilized along the direction of the total magnetic field, and the output is recorded on a paper chart at a sensitivity of about 1 γ full scale. This magnetometer contains a bandpass filter with 3-db points at 0.07 and 0.7 cps. The time axis of this recorder is driven by a dc motor and hence is not as accurate as the chart drive for the rubidium vapor magnetometer.