The nature of worldwide geomagnetic disturbances generated by the Starfish explosion of July 9, 1962

Abstract

A new approach was used to study the worldwide effects recorded by standard magnetometers a few minutes after the Starfish detonation. The magnitudes of the total disturbance were plotted on a world map and, by the use of standard contouring techniques, global lines of equal signal strength were obtained. In this system of isopleths, an outstanding feature is a pair of clearly defined maximums located near the geomagnetic meridian of the source and centered at geomagnetic latitudes of about 45° North and South, whereas there is a relatively low value near the shot location. Another innovation was the introduction of a coordinate system based upon the geomagnetic field direction at each station; one axis (called a) is along the dipole field line and the other two orthogonal axes lie in the plane (called p) perpendicular to the dipole field. The close resemblance between the isopleths of the p component and those of the total disturbance (at 3 min postshot) indicates that the major portion of the signal was in the p plane at that time. The a pattern, while more complicated than the p, clearly exhibits certain symmetries that are described and tentatively identified. To account for the two p maximums a possible mechanism was advanced, namely, that the pattern is the result of coupling of energy from the isotropic, modified Alfvén mode into transverse, pure Alfvén waves in regions where favorable coupling conditions exist.

Anthropogenic Space Weather

“…Auroral observations following Starfish (Gabites and Rowles, 1962) support a very prompt activity at higher magnetic latitudes, in the mid-40 • range, than the conjugate area of explosion site. The conclusions of Bomke et al (1966), together with the observation of auroral activity confirm that the magnetic field lines in the vicinity of the meridian plane of the explosion site were strongly disturbed to much greater heights and magnetic latitudes than was the case for the earlier, 1958 series of nuclear detonations. In particular the sketch in Fig.…”

“…The ∼2 second delay is then accounted for by the initial propagation delay along the magnetic field line. A very comprehensive modeling of the geomagnetic observations in the form of iso-intensity contours of the magnetic disturbances by Bomke et al (1966) have yielded the unexpected result that the maxima were in magnetically conjugate regions about the Johnston Island magnetic meridian plane, but at 45 • magnetic latitude, rather than closer to the Johnston Island magnetic latitude of 14 • N (see Fig. 34).…”

“…Values are in gammas. A contour interval of 10 gammas is used from the 10-gamma isopleth upward; the color lines are 10, 50, 100, and 150 gammas (fromBomke et al, 1966).…”