Abstract
The new Release-06 (RL06) Gravity Recovery and Climate Experiment (GRACE) gravity field solutions are evaluated by converting them into equatorial effective angular momentum functions (so-called excitation functions) for polar motion and comparing these to respective time series based on space-geodetic observations (geodetic excitation). The same is performed for the older RL05 solutions using identical processing. Maps of equivalent water heights derived from both releases show that the signal-to-noise ratio is significantly improved in RL06. The derived polar motion excitation functions from RL05 and RL06 differ by about 15%. An analysis of the contributions of different Earth subsystems revealed that the release update mainly influenced the hydrological (12%) and oceanic excitations (17%), but it has a relatively small impact on the cryospheric excitations related to Antarctica (4%) and Greenland (1%). The RL06 data from different GRACE processing centers are more consistent among each other than the previous RL05 data. Comparisons of the GRACE-based excitation functions with the geodetic and model-based oceanic excitations show that the latest release update improved the agreement by about 2 to 15 percentage points.
Highlights
Mass displacements within the Earth system cause variations of the Earth’s gravity field and its rotation
In analogy to the previous section, we investigate the differences of the excitation functions derived from the Gravity Recovery and Climate Experiment (GRACE) RL06 solutions from Center for Space Research (CSR), Jet Propulsion Laboratory (JPL), and GFZ and Institute of Theoretical Geodesy and Satellite Geodesy (ITSG)-Grace2018
While the integral effect of the mass-related polar motion excitation can be directly derived from the potential coefficients C21 and S21 (GSM + GAC), the determination of individual contributions from the Earth’s subsystems is based on the full set of potential coefficients (GSM + GAD) and requires adequate filtering and masking
Summary
Mass displacements within the Earth system cause variations of the Earth’s gravity field and its rotation. Temporal variations of the gravity field can be used to study the mass-related excitation of polar motion. It was shown that due to the release update from RL04 to RL05 the agreement between GRACE-derived effective angular momentum functions and the mass-related part of the so-called geodetic excitations (Brzeziński 1992) could be slightly improved. The latter can be derived from Earth Orientation Parameter (EOP) time series, such as EOP 14 C04 (Bizouard et al 2014) of the International Earth Rotation and Reference Systems Service (IERS), reduced by the motion-related effects within the atmosphere (winds) and oceans (currents) based on geophysical model data.
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