Varved sequences represent imperfect metorologic time series that lend themselves to harmonic analysis. Both Fourier (amplitude) and power (variance) spectrum analyses have been used in the study of several varve types; the first for maximum resolving power and the second for stability and the study of gross variation of the spectrums. Weak, changing periodic tendencies at the higher frequencies (2 to 20 years)—that might he confused with white noise, but seem to be inherent in climatic data—are present in all series. A few periods seem slightly favored, but none corresponding to the sunspot period of 11+ years was noted. Varve series believed to be sensitive to temperature changes exhibit more power at the lower frequencies than series in which precipitation or other factors are thought to be the principal control. The low frequencies also show a tendency toward periodicity near 90 years that might be related to solar activity.
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