Atmospheric and oceanic forcing of the rapid polar motion |
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Authors: | Christian Bizouard L Seoane |
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Institution: | (1) Space Research Centre, Polish Academy of Sciences, Bartycka 18A, 00-716 Warsaw, Poland |
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Abstract: | The rapid polar motion for periods below 20 days is revisited in light of the most recent and accurate geodetic and geophysical
data. Although its amplitude is smaller than 2 mas, it is excited mostly by powerful atmospheric processes, as large as the
seasonal ones. The residual amplitude, representing about 20% of the total excitation, stems from the oceans. Rapid polar
motion has an irregular nature that is well explained by the combined influence of the atmosphere and the oceans. An overall
spectrum reveals cycles principally at 20, 13.6 (fortnightly tidal period) and 10 days (corresponding to the normal atmospheric
mode Y31{\Psi_3^1}), but this is only an averaged feature hiding its strong variability over seasonal time scales. This explains why it is so
delicate to determine an empirical model of the tidal effect on polar motion. The variability in both amplitude and phase
of the 13.6-day term is probably caused by a lunar barometric effect, modulated by some sub-seasonal thermal processes. The
irregularities of the prominent cycles of the short-term polar motion are well explained by the atmospheric and oceanic excitations.
The oceanic variability reinforces the atmospheric one, as they were triggered by the same agent, maybe seasonal and inter-annual
thermal variations. |
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Keywords: | |
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