Assessing the impact of corrections included in the GRACE Level-3 data on gravimetric polar motion excitation estimates

Abstract

Between 2002 and 2017, the Gravity Recovery and Climate Experiment (GRACE) mission provided datasets of temporal variations of the Earth’s gravity field, among others in the form of maps of terrestrial water storage (TWS) changes (Level-3 datasets). This paper examines the impact of several corrections included in the GRACE Level-3 data on the estimated series of hydrological plus cryospheric angular momentum (HAM/CAM). We tested the role of removing the glacial isostatic adjustment (GIA) signal, adding degree-1 coefficients of geopotential (DEG1 correction), replacing the degree-2 zonal coefficient with a more accurate estimate from satellite laser ranging (C20 correction), and restoring ocean bottom pressure geopotential coefficients (GAD). The contribution of improved separation of land and ocean signals by using the Coastal Resolution Improvement (CRI) filter was also assessed. We examined the change in agreement between HAM/CAM and the hydrological plus cryospheric signal in geodetically observed excitation (geodetic residuals, GAO) when the corrections are applied. The results show that including GIA, DEG1, C20, and GAD corrections in the GRACE data increases HAM/CAM trends and reduces overall HAM/CAM variability. The exploitation of corrections slightly heightens consistency between HAM/CAM and GAO for χ1 and χ2 in the non-seasonal spectral band and for χ1 in the seasonal spectral band. The results from this study demonstrate how the different corrections combine to make the overall improvement in agreement between HAM/CAM and GAO and which corrections are most valuable.