Rapid geomagnetic fluctuations at Tucson, Arizona

Abstract

Oscillatory fluctuations (micropulsations), appearing as trains of waves in the frequency range of 1/2 to 1/32 cps, were present about 20 pct of the time, with amplitudes of 0.01γ or more, in records of the vertical component of field made at Tucson with a large buried loop in the summer of 1947. The amplitudes of the oscillations were inversely proportional to their frequencies, and 1/20‐cps oscillations occurred more often than those of other frequencies. The highest frequencies occurred at night and were related to times of large magnetic disturbance; the lowest frequencies occurred during the day at times of low or moderate activity, and the intermediate frequencies showed a transition of behavior. Random fluctuations, having no characteristic wave forms, had amplitudes which varied as the square root of the fluctuation duration. Average amplitudes of the three largest fluctuations per 15‐min scaling interval decreased from 0.08γ at 60‐sec duration to 0.01γ at one second; maximum amplitudes were about ten times these values. The random fluctuations also showed diurnal variations and a dependence on the degree of magnetic disturbance. A few audio‐frequency measurements are also reported.