Nontidal oceanic contributions to gravitational field changes: Predictionsof the Parallel Ocean Climate Model

This study examines the nontidal contributions of the oceans to the Earth's gravitational field variations as predicted by a global ocean general circ ulation model: the Parallel Ocean Climate Model. Such variations in the gra vitational field Stokes coefficient are determined up to spherical harmonic degree and order 20 and compared with satellite laser ranging (SLR) data f rom LAGEOS I and LAGEOS II. For most Stokes coefficients except the lowest- degree ones, this investigation indicates that the application of sea level adjustment to reduce the effects of the model's lack of mass conservation due to the Boussinesq approximation has a negligible effect on timescales l ess than a few years. Predicted gravitational changes show strong seasonal variability and account for a portion of the variations estimated from SLR. We conclude that, in addition to the atmosphere, the oceans are an importa nt contributor to the temporal variations in the Earth's gravitational fiel d. The Stokes coefficients are useful in examining oceanic mass transport b etween hemispheres and ocean basins. The estimated oceanic power spectrum h as a spectral shape similar to the atmosphere and is well above the noise l evel of planned satellite missions like the Gravity Recovery and Climate Ex periment (GRACE).