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3.2.2.3.2. Pole tides

The ocean pole tide is the ocean response to the variation of both the solid Earth and the oceans to the centrifugal potential that is generated by small perturbations to the Earth's rotation axis.

Amplitude in cm of the pole tide correction during the Jason-1 cycle 223 computed from an equilibrium model. This map is drawn using the Basic Radar Altimetry Toolbox from the Jason-1 GDR products. A Loess filter (value of 31) is applied to obtain a fully coloured plot.

These small perturbations to the Earth's rotation axis primarily occur at periods of 433 days (called the Chandler wobble) and annual. These periods are long enough for the pole tide displacement to be considered to be in equilibrium with the forcing centrifugal potential. Results from satellite altimetry demonstrate that the long-wavelength component of the geocentric pole tide deformations at the Chandler period is consistent with the theoretical self-consistent equilibrium response and can explain 70% of variations of the theoretical classical equilibrium response [Desai, 2002].

The pole tide is easily computed as described in Wahr [1985]. Modelling the pole tide requires knowledge of proportionality constants, the so-called Love numbers, and a time series of perturbations to the Earth's rotation axis, a quantity that is now measured routinely with space techniques.

Further information:

• Desai S. D., Observing the pole tide with satellite altimetry , J. Geophys. Res., 107(C11), 3186, doi:10.1029/2001JC001224, 2002.
• Wahr J. M., Deformation induced by polar motion, J. Geophys. Res., 90(B11): 9363 - 9368, 1985.