Role of ocean currents and bottom pressure variability on seasonal polar motion

Author: Rui M. Ponte and D. Stammer
July 20, 1999
Journal Article
Journal of Geophysical Research

Ponte, R. M., and D. Stammer (1999), Role of ocean currents and bottom pressure variability on seasonal polar motion, J. Geophys. Res., 104(C10), 23,393–23,409, doi:10.1029/1999JC900222.

Changes in the ocean angular momentum (OAM) components about the equatorial axes, either due to fluctuations in currents or bottom pressure (mass redistribution), can induce movements of the Earth's pole of rotation, commonly referred to as polar motion or wobble. Output from a 1° resolution ocean model is used to calculate the effective equatorial OAM functions χ 1 O and χ 2 O , corresponding to polar motion excitation about the equatorial axis pointing to the Greenwich and 90°E meridians, respectively. Time series of χ O are combined with similar atmospheric series χ A , computed from the National Centers for Environmental Prediction/National Center for Atmospheric Research reanalyses, to interpret the observed low-frequency polar motion excitation for the period 1985–1996. Results indicate that the oceans are a very important excitation source for the Chandler (∼433 days), annual, and semiannual wobbles, providing for much better amplitude and phase agreement with the observed excitation at these periods, in comparison with what is obtained when only the atmosphere is considered. Both oceanic mass and motion terms are found to be important but with mass signals having somewhat larger amplitudes. The role of regional variability in ocean currents and bottom pressure in contributing to χ O signals is quantified. Midlatitude regions (∼30°–70°) figure prominently as places of strong local oceanic excitation signals. The North Pacific basin is found to be generally important for χ 1 O excitation, while the Southern Ocean is important for both χ 1 O and χ 2 O . The largest positive covariances of local with global χ O signals occur in the Kuroshio region near the western boundary of the North Pacific for χ 1 O and southwest of Australia for χ 2 O