Evaluating GRACE Mass Change Time Series for the Antarctic and Greenland Ice Sheet—Methods and Results

Abstract

Satellite gravimetry data acquired by the Gravity Recovery and Climate Experiment (GRACE) allows to derive the temporal evolution in ice mass for both the Antarctic Ice Sheet (AIS) and the Greenland Ice Sheet (GIS). Various algorithms have been used in a wide range of studies to generate Gravimetric Mass Balance (GMB) products. Results from different studies may be affected by substantial differences in the processing, including the applied algorithm, the utilised background models and the time period under consideration. This study gives a detailed description of an assessment of the performance of GMB algorithms using actual GRACE monthly solutions for a prescribed period as well as synthetic data sets. The inter-comparison exercise was conducted in the scope of the European Space Agency’s Climate Change Initiative (CCI) project for the AIS and GIS, and was, for the first time, open to everyone. GMB products generated by different groups could be evaluated and directly compared against each other. For the period from 2003-02 to 2013-12, estimated linear trends in ice mass vary between −99 Gt/yr and −108 Gt/yr for the AIS and between −252 Gt/yr and −274 Gt/yr for the GIS, respectively. The spread between the solutions is larger if smaller drainage basins or gridded GMB products are considered. Finally, findings from the exercise formed the basis to select the algorithms used for the GMB product generation within the AIS and GIS CCI project.

Mass Balance of the Greenland Ice Sheet from GRACE and Surface Mass Balance Modelling

“…It complements GRACE's inability to detect small glaciers. These results, based on the combined processing of the GRACE and SMB data, revealed that the GrIS total mass within the entire investigated period decreased at an annual rate of −267.77 ± 8.68 Gt/yr, and this accelerated by −12.12 ± 2.59 Gt/yr 2 , which is comparable with previous studies (e.g., the range −252 Gt/yr to −274 Gt/yr from Groh et al (2019) [48]; −255 Gt/yr from the Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) team (2019) [49]). During the same period, the Antarctic ice sheet's mass change rate was −162.91 ± 5.09 Gt/yr, with an acceleration of 10.12 ± 4.3 Gt/yr 2 .…”

Return to rapid ice loss in Greenland and record loss in 2019 detected by the GRACE-FO satellites

“…The gravity field signal arising from each basin and Ellesmere Island is calculated in the spectral domain, filtered identical to the GRACE/GRACE-FO data, and then adjusted in scale for each basin to least-squares minimize the difference between the modelled and observed spatial gravity field signal over the GrIS and Ellesmere Island. Using alternate GrIS mass change times series available at http://gravis.gfz-potsdam.de/home, which is based on the inversion schemes of 59 , as well as using AV RL06 with the inversion approach of 28 , we estimate that different assumptions underlying the gravimetric inversion introduce an uncertainty of ±25 Gt for the monthly estimate. These values are consistent with the ±26 Gt uncertainty presented in Table A.1 of 27 and included in our GrIS time series.…”

Decade-long shift in the rate of global mean sea-level rise

“…To isolate LWS in GRACE mascon, we removed the glacier signals from the data over land based on Wouters 63 . The standard error is based on noise assessment by Groh 64 . Prior to the GRACE period, information on the LWS component comes from reanalysis products over 1993-2002: Modern Era Retrospective-analysis for…”