Developing the SAGSA L3 gravimetry ensemble and its applications

Abstract

Since 2002, the GRACE and GRACE-FO satellite missions have been monitoring monthly variations in the gravitational field caused by mass redistributions within the Earth’s system. To extract information on the global and regional water cycle, estimates of the gravity field must be corrected to account for several instrumental and geophysical processes. The SAGSA L3 dataset uses an ensemble approach to estimate water mass redistributions in the ocean, atmosphere, hydrosphere, and cryosphere, as well as their uncertainties. Here, we review the processing and post-processing steps included in the ensemble approach, with a particular focus on the dry mass of the atmosphere and leakage from the continents to the oceans. A small-amplitude drift has been identified in the global average estimate of atmospheric mass, affecting the standard ERA-5 reanalysis and all dealiasing models derived from it. We show that the global atmospheric mass correction has a significant impact on ocean applications, reducing the sea level budget residuals by approximately 2 mm between 2016 and 2026. In addition, a new framework has been established to better correct leakage errors, which are linked to the mislocation of water mass variations along coastlines. The new leakage correction allows for a better redistribution of water masses along the coastline, which has a significant impact on estimates of glacier mass balance (up to 30 Gt/yr across all glaciers) as well as on sea level variations near the coast (up to 2 mmSLE) between 2002 and 2026. While current efforts enable the SAGSA ensemble to contribute to leading international research initiatives—such as the validation of simulations used for future missions or glacier mass balance comparison exercises— additional efforts are needed to improve the accuracy of water mass distribution estimates, particularly with regard to post-processing corrections related to solid Earth deformations (i.e., glacial isostatic adjustment, co- and post-seismic deformations, as well as hydrological and oceanic loads).