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On the Regularity of Fluctuations in Annual and Secular Polar Motions

Published online by Cambridge University Press:  27 June 2016

H. J. Abraham
H. J. Abraham*
Affiliation:
Mount Stromlo and Siding Spring Observatories, Research School of Physical Sciences, The Australian National University

Abstract

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It may become possible to explain much of the behaviour and remarkable regularity of fluctuations in reported annual and secular polar motions if the potential that causes an immediate excitation is also a factor in that excitation's rate of change afterwards.

The Chandler frequency, for example, being a function of the deformation excitation, should then vary with the librational and nutational displacements of the pole of rotation. It is found that the frequency does in fact do so.

The annual excitation would be affected as well. The steady and seasonal primary excitations are known to cause free and forced nutations that are accompanied by periodic secondary excitations. These would arise partly at once and partly in the course of time; they would modulate the primary annual excitation and also one another, according to the period of the beats between the annual and Chandler nutations. It is found that the reported annual excitation shows phase and amplitude fluctuations of this kind. (The data also show another large excitation that occurred briefly on two occasions).

Finally, the amplitude and phase of the secular librations appear to have followed an expression that is obtained by integrating the rates of change of excitation. This expression is a function of the amplitude of the annual excitation and the period of the beats between the annual and Chandler nutations.

Type
Research Article
Information
Symposium - International Astronomical Union , Volume 48: Rotation of the Earth , 1972 , pp. 61 - 67
Copyright
Copyright © Reidel 1972 

References

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