Exploring the uncertainty in GRACE estimates of the mass redistributions at the Earth surface: implications for the global water and sea level budgets

Blazquez, A. ; Meyssignac, B. ; Lemoine, J. M. ; Berthier, E. ; Ribes, Aurélien ; Cazenave, A.

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<p align="justify">Observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission provide quantitative estimates of the global water budget components. However, these estimates are uncertain as they show discrepancies when different parameters are used in the processing of the GRACE data. We examine trends in ocean mass, ice loss from Antarctica, Greenland, arctic islands and trends in water storage over land and glaciers from GRACE data (2005-2015) and explore the associated uncertainty. We consider variations in six different GRACE processing parameters, namely the processing centre of the raw GRACE solutions, the geocentre motion, the Earth oblateness, the filtering, the leakage correction and the glacial isostatic adjustment (GIA). Considering all possible combinations of the different processing parameters leads to an ensemble of 1500 post-processed GRACE solutions, which is assumed to cover a significant part of the uncertainty range of GRACE estimates. The ensemble-mean trend in all global water budget components agree within uncertainties with previous estimates based on different sources of observations. The uncertainty in the global water budget is ±0.27 mm yr−1 [at the 90 per cent confidence level (CL)] over 2005-2015. We find that the uncertainty in the geocentre motion and GIA corrections dominate the uncertainty in GRACE estimate of the global water budget. Their contribution to the uncertainty in GRACE estimate is respectively ±0.21 and ±0.12 mm yr−1 (90 per cent CL). This uncertainty in GRACE estimate implies an uncertainty in the net warming of the ocean and the Earth energy budget of ±0.25 W m−2 (90 per cent CL) when inferred using the sea level budget approach.</p>
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