On the Long-Period Variations in the Rate of the Earth’S Rotation

Abstract

The maximum entropy power spectrum (Smylie, et al., 1974) of the Earth’s rotational speed was calculated using data from 1900 to 1976. Two series of data were analyzed. The first was a series of δψ/ψ determined from annual UT1 — ET data from 1900 to 1976. The second was a similar series derived from the mean monthly data of UT1 — TAI. Linear trends were removed from both series before analysis. Using the second series of data, significant periods of 2.8, 3.7, 7.0, and 10.5 years were found. The first series showed significant periods at 6, 10, 13, 22, and 57 years. Of these periodicities those at 22 and 57 years showed the largest amplitudes (0.454 ± 0.097 × 10−⁸ and 1.431 ± 0.104 × 10−⁸ respectively).