Oceanic influence on the annual polar motion

Oceanic contributions to the seasonal wobbles of polar motion are evaluated using three different ocean circulation models: (a) the Parallel Ocean Climate Model; mass term only, i.e. tensor of inertia changes; (b) the model used by Ponte et al. (1998) (Ponte R.M., Stammer D., Marshall J., 1998. Oceanic signals in observed motions of the Earthʹs pole of rotation, Nature 391, 476–479 (mass term+motion term); (c) the model by Thomas and Sündermann (1998) (Thomas M., Sündermann J., 1998. Zur simultanen Modellierung von allgemeiner Zirkulation und Gezeiten im Ozean und Auswirkungen auf bestimmte Erdrotationsparameter. In: Freeden, W., (Ed.), Progress in Geodetic Science, Aachen, pp. 144–151) (mass term+motion term). The equatorial excitation components chi1, and chi2 describe an ellipse as the superposition of prograde and retrograde circular components at each frequency. The excitation ellipses are given at annual, semi-annual and thrice-yearly periods. These ellipse parameters are compared to differences: (excitation from observations) – (atmospheric part). The model by Ponte et al. nearly closes the balance.