Power spectra of geomagnetic fluctuations between 0.02 and 20 Hz
Beard, Michael Wayne
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Fluctuations of the East-West component of the Earth's geomagnetic field were measured at a remote land site. The resulting data were transmitted by a solar powered telemetry system to the Naval Postgraduate School at Monterey, California, and the power spectra for the frequency range of .02 - 20 Hz calculated. The measurements, which covered a 4-month interval (July 20 - October 10, 1981), consistently show a minimum of activity in the interval 3 - 7 Hz. At frequencies below the minimum, in the range of .02 - 3 Hz , the typical monotonic decrease in background activity with frequency was observed. At 1 Hz an average power spectral density of 1X10" 2 nT2 /Hz was observed during the day and 3.1X10" 3 nT 2 /Hz at night a In contrast, at frequencies above the minimum, in the range 7-14 Hz, the activity is dominated by the first Schumann resonance. An evaluation of the East-West component spectra and concurrent underwater horizontal component measurements showed a 90% correlation with the underwater spectra. The underwater field strengths were normally 3-5 dB less than the strengths measured on land. Splitting of the first Schumann resonance peak into a doublet structure was observed in 10% of the land data.
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