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Great variability exists in the day to day characteristics of power spectrums of geomagnetic field variations at the earth's surface. Statistically stable average spectrums are needed for purposes such as comparison with spectrums of magnetic fluctuations recorded at other latitudes or recorded in the magnetosphere by satellites, or comparison with theoretically predicted surface spectrums [Field and Greifinger, 1965; Prince and Bostick, 1964].
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T. J. Herron (1967) studied this question.
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