Analysis of geomagnetic micropulsations due to high-altitude nuclear explosions

Abstract

Spectrums of the magnetic disturbances from the high-altitude nuclear explosion of July 9, 1962, computed from flux-rate variograph recordings obtained at Huancayo, Peru; Uppsala, Sweden; Reykjavik, Iceland; and Resolute Bay, Canada; are compared with those computed for several natural sudden commencements. The sudden commencement data show a lack of distinct spectral peaks compared with the spectrums of the nuclear explosion. The Alfven velocity-altitude profile indicates that MHD waves can be trapped in a waveguide in the altitude range from 300 to 3000 km, thus producing resonant oscillations in the waveguide. The line nature of the explosion spectrums suggests that a resonance mechanism is appropriate. A review of the theory for a simple MHD resonance model is presented, and computed eigenfrequencies are compared with the observed data. The observed data are in fair agreement with theoretical predictions. An interesting feature of the present study is the evaluation of the dimensionless dissipation parameter Q, which is of the order of 1 to 10 for MHD waves, suggesting that simplifying assumptions neglecting energy dissipation mechanisms must be dropped.