Learning from ocean bottom pressure differences between GRACE and a state estimate constrained by GRACE

Abstract

Observations from GRACE and its follow-on mission have been used to constrain the ocean bottom pressure (OBP) fields in the state estimates produced by the project for Estimating the Circulation and Climate of the Ocean (ECCO). Here we examine the OBP residuals, i.e., the remaining differences between a recent optimized ECCO solution and the GRACE data, to identify potential issues with both the observations and the ocean model used in ECCO. The GRACE-ECCO residuals are dominated by long-term trends and seasonal variability and exhibit mostly large-scale structures. The trends can be partly related to unmodeled earthquake signals and gravitational, rotational and deformational (GRD) effects on the GRACE-derived OBP fields. Land hydrology processes and associated GRD effects can also contribute to seasonal residuals. In regions of high eddy energy (e.g., Agulhas Retroflection, Gulf Stream), residuals are partly caused by the impact of mesoscale signals on GRACE-derived OBP fields, which is not represented in the coarse-resolution ECCO model.  Other possible contributions to the residuals include uncertainties in glacial isostatic adjustment models and poor horizontal resolution in both data (leakage of land signals in GRACE retrievals) and model (inadequate representation of coastal domains).