Evaluation of GRACE Mascon Gravity Solution in Relation to Interannual Oceanic Water Mass Variations

With evidence of an accelerated water cycle over the past few decades, we make inferences on the spatial variability of interannual evaporation and precipitation patterns from 2003 to 2014 gravity anomalies, using the Gravity Recovery and Climate Experiment (GRACE) satellite mascon data set. Comparison of the mascon solution with an ensemble harmonic solution is conducted, along with validation over the oceans via sea surface height from multimission altimetry minus Argo floats data/GECCO2 [the GECCO2 ocean synthesis is the German contribution to Estimating the Circulation and Climate of the Ocean project (www.ecco-group.org)] steric sea level. The mascon solution was consistently more accurate than its spherical harmonic counterpart across large spatial and temporal scales, due mainly to the inherent smoothing from the mascon cells. Comparison of GRACE with both GECCO2 + altimetry and Argo + altimetry mass estimates revealed an offset in phase with regard to the annual cycle, but yielded an rmse of only 5.6 mm in the interannual signal after phase correction. This paper furthers evidence of an accelerated water cycle at a rate of 1.5% ± 1.1% at low latitudes, and provides a means of validation for oceanic freshwater budget studies based on salinity measurements.

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