Observations of hydromagnetic emissions

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The paper deals with preliminary results of a frequency-time analysis of geomagnetic micropulsations in the frequency range 0.5–5 cps. The data from which these results derive were recorded near Palo Alto, California, November 18–21, 1960. At times, oscillatory signals of slowly varying frequency were observed continuously for periods of many hours. Signals of more rapidly varying frequency were also observed, but for shorter periods of time, usually 10 to 30 minutes. Oscillations at the same frequencies were found to occur simultaneously on waveform records obtained at California Institute of Technology stations near Ely, Nevada, and near Isabella and Mount Palomar, California. The oscillations are called hydromagnetic (hm) emissions, since preliminary evidence implies that they are generated either above or high in the ionosphere and are propagated downward by hydromagnetic waves. The period preceding and including the interval during which data were obtained was characterized by solar-flare activity that produced a number of geophysical effects and undoubtedly influenced the nature of the oscillations.