A comparison of model and GRACE estimates of the large-scale seasonal cycle in ocean bottom pressure

Seasonal variability in ocean bottom pressure p(b) is analyzed using GRACE ( Gravity Recovery and Climate Experiment) data products and an optimized model solution obtained by fitting most available ocean data in a least-squares sense. The annual cycle in the spatial mean is a substantial part of the observed seasonal pb variability; net freshwater input and atmospheric pressure effects are both important. For the residual spatially-varying patterns, GRACE and model results agree well over the Southern Ocean where strongest variability at both annual and semiannual periods is present. Phase patterns tend to match well, although model amplitudes are generally weaker. Considerable uncertainty remains in both GRACE and model pb fields, judging from the spread among available estimates. Improving the pb estimates requires removal of data noise from aliasing and leakage of land hydrology signals, and further optimization of the ocean model, including possible use of GRACE data to constrain the solution.