Oceanic angular momentum variability estimated from the Parallel Ocean Climate Model, 1988-1998

This paper describes the use of a global numerical model of the oceans to e stimate variations in both the equatorial and axial components of angular m omentum resulting from oceanic mass redistribution and circulation. The Par allel Ocean Climate Model, driven by daily wind fields and monthly heat flu xes from the European Gentle for Medium-Range Weather Forecasts for 1988-19 98, provides insight into variations in the transport and exchange of angul ar momentum, a quantity which is essentially conserved within the Earth sys tem. Exchange of angular momentum between the oceans and tl-Le solid Earth should be manifest as changes in the Earth's rotation (both polar motion an d length of day), and it is possible to compare predicted Earth rotation ch anges with actual geodetic observations. Using an inverted barometer assump tion for oceans, the numerical model predictions of rotation change agree i n sign and magnitude and are significantly correlated with observed polar m otion and length of day variations after subtracting the dominant atmospher ic contributions. The correlation has a seasonal variation which suggests t hat the role of the oceans in the excitation polar motion is more important during the Northern Hemisphere summer. Our results indicate that the ocean s, to a different extent, account for a significant part of the nonatmosphe ric angular momentum budget for the Earth, and its fluid envelopes on inter annual to submonthly timescales.