Abstract
Geocenter variations relate the motion of the Earth’s center of mass with respect to its center of figure, and represent global-scale redistributions of the Earth’s mass. We investigate different techniques for estimating of geocenter motion from combinations of time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On missions, and bottom pressure outputs from ocean models. Here, we provide self-consistent estimates of geocenter variability incorporating the effects of self-attraction and loading, and investigate the effect of uncertainties in atmospheric and oceanic variation. The effects of self-attraction and loading from changes in land water storage and ice mass change affect both the seasonality and long-term trend in geocenter position. Omitting the redistribution of sea level affects the average annual amplitudes of the x, y, and z components by 0.2, 0.1, and 0.3 mm, respectively, and affects geocenter trend estimates by 0.02, 0.04 and 0.05 mm/yr for the the x, y, and z components, respectively. Geocenter estimates from the GRACE Follow-On mission are consistent with estimates from the original GRACE mission.
Highlights
Variations in the Earth’s geocenter reflect the largest scale variability of mass within the Earth system, and are essential inclusions for the complete recovery of surface mass change from time-variable gravity [1,2]
Sets of coefficients are constructed using estimates of terrestrial water storage (TWS) calculated from the Global Land Data Assimilation Systems (GLDAS) NOAH land surface model [53], estimates of surface mass balance (SMB) change for glaciers and ice caps calculated from the Regional Atmospheric and Climate Model (RACMO2.3) [54,55] and estimates of Greenland and Antarctic ice sheet mass balance from the mass budget method (MBM) [56]
We investigate the effects of different calculations of the eustatic sea level caused by changes in land mass for estimating geocenter variations from combinations of ocean model outputs and time-variable gravity measurements from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On missions
Summary
Variations in the Earth’s geocenter reflect the largest scale variability of mass within the Earth system, and are essential inclusions for the complete recovery of surface mass change from time-variable gravity [1,2]. Estimates of geocenter position have important applications in the determination of terrestrial reference frame variations, satellite altimeter orbit fluctuations, and mass transport from time-variable gravity [1,5]. Variations in geocenter have been attributed to changes in terrestrial water storage, glacier and ice sheet mass, atmospheric and oceanic circulation, geodynamic processes and other mass transport processes, Figure 1 [1,6,7,8]. Measurements of time-variable gravity from the Gravity Recovery and Climate Experiment (GRACE) and the GRACE Follow-On (GRACE-FO) missions are set in a center of mass (CM) reference frame, in which the total degree one variations are inherently zero [9,10,11].
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