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Ivashchenko N. N., Sidorenkov N. S., Sonechkin D. M. Study of the earth’s pole motion using a mapping on an external force period. *Izvestiya VUZ. Applied Nonlinear Dynamics*, 2007, vol. 15, iss. 4, pp. 84-91. DOI: 10.18500/0869-6632-2007-15-4-84-91

# Study of the earth’s pole motion using a mapping on an external force period

It is known from astronomic observations that the motions of the North pole of the Earth consist of a trend to the Greenland direction, and a rotational component superimposed on the trend. The periods of 12 and about 14 months these motions. The first period is resulted from the seasonal mass redistribution in atmosphere and oceans. The second period is its called the Chandlerian and nature is vague. Because of incommensurability of both periods each with another one can see six/sevel year beats in the time series of the Earth’s pole coordinates. It is not known definitely what is the character of these beats. The aim of this paper is to clear up this question using the most accurate time series of the North pole coordinates covering the time from 5 January 1962 up to 18 July 2004 (sampled over 5 day period). A mathematical technique of mapping is used for the phase trajectory section chosen at the annual period of the external force. It is found that the beat frequency varies by a quasi-periodic manner, and the beat amplitude is seasonal dependent one.

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