Ocean bottom pressure from model and GRACE estimates

Author: Rui M. Ponte, Katherine J. Quinn, C. Wunsch and P. Heimbach
July 2, 2007
XXIV IUGG General Assembly, Perugia, Italy

Ponte, R.M., K.J. Quinn, P. Heimbach, and C. Wunsch, 2007. Ocean bottom pressure from model and GRACE estimates, XXIV IUGG General Assembly, Perugia, Italy, July 2007, invited.

Large-scale low frequency variability in ocean bottom pressure is analyzed using GRACE (Gravity Recovery and Climate Experiment) data products and an optimized model solution from the ECCO-GODAE (Estimating Circulation and Climate of the Ocean-Global Ocean Data Assimilation Experiment) project. The optimized ECCO-GODAE estimate is obtained by fitting most available ocean data in a least-squares sense, using best known statistics of model and data errors. Variability in the spatial mean is a substantial part of the observed bottom pressure signal, particularly at the seasonal timescale; 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 annual and semiannual periods is present. Phase patterns tend to match well, although model amplitudes are generally weaker. We experiment with various GRACE products and model solutions to
derive estimates of uncertainty for the bottom pressure estimates and discuss the use of time-varying GRACE data to constrain the model solutions.