Oceanic signals in observed motions of the Earth's pole of rotation

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Abstract

Motion of the Earth's pole of rotation relative to its crust, commonly referred to as polar motion, can be excited by a variety of geophysical mechanisms1. In particular, changes in atmospheric wind and mass fields have been linked to polar motion over a wide range of timescales, but substantial discrepancies remain between the atmospheric and geodetic observations1,2,3,4. Here we present results from a nearly global ocean model which indicate that oceanic circulation and mass-field variability play important roles in the excitation of seasonal to fortnightly polar motion. The joint oceanic and atmospheric excitation provides a better agreement with the observed polar motion than atmospheric excitation alone. Geodetic measurements may therefore be used to provide a global consistency check on the quality of simulated large-scale oceanic fields.

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Figure 1: Five-day averaged values of χ1O and χ2O for the period January 85–April 96.
Figure 2: Power spectral density for oceanic χ1P (solid line), χ1V (dotted), χ2P (dashed) and χ2V (dotted-dashed) calculated by averaging respective periodograms over 20 adjacent frequencies.
Figure 3: Assessment of oceanic effects on the excitation of polar motion.

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Acknowledgements

We thank D. Spiegel for help with the computation, and F. Bryan, B. Chao, R. Rosen and D. Salstein for comments. This work was supported by NASA's Mission to Planet Earth.

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Correspondence to Rui M. Ponte.

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