Abstract
Differential equations ruling the Earth’s polar motion are slightly asymmetric with respect to the pole coordinates. This is not only associated with the lack of axial symmetry around the Earth figure axis (triaxiality) but also with the longitude dependency of the pole tide (the main contribution). We propose a consistent handling of both asymmetric contributions, formulating a unique equation in the complex equatorial plane, of which we derive a general solution. Difference with respect to the usual symmetric solution is discussed and found significant in light of the present accuracy of the observed pole coordinates. For the same geophysical excitation, the prograde Chandler wobble is accompanied by a retrograde component up to 2 milliarcseconds (mas), transforming it in a slight elliptic motion. The asymmetric contribution is relatively larger in the geodetic excitation function, for Chandler wobble excitation mixes prograde and retrograde components of comparable level (1 mas).
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Notes
The equatorial path of a pseudo-periodic component of the polar motion is an ellipse resulting from the combination of two opposite uniform circular motions. The corresponding ellipticity is called intrinsic when it purely results from the Earth’s property regardless of the excitation.
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Acknowledgments
The second author is supported by Chinese Academy of Sciences Fellowship for Young International Scientists and RFBR Grant 12-02-31184. We greatly thank the reviewers for their remarks and corrections. One of them, by doing a very careful review, and making us aware of the work of Okamoto and Sasao (1977), permitted us to refine this study.
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Bizouard, C., Zotov, L. Asymmetric effects on Earth’s polar motion. Celest Mech Dyn Astr 116, 195–212 (2013). https://doi.org/10.1007/s10569-013-9483-x
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DOI: https://doi.org/10.1007/s10569-013-9483-x