Present-Day Geocenter Interannual Variations
Kuo, Chungyen1; Guo, Junyi2; Shum, C.K.2; Huang, Zhenwei2; Duan, Jianbin2
1Department of Geomatics, National Cheng Kung University, TAIWAN; 2Ohio State University/School of Earth Sciences, UNITED STATES

Geocenter variations, the motion of the Center of Mass (CM) of the Earth system relative to its Center of Figure (CF), have been traditionally estimated using SLR, GPS, or DORIS satellite tracking data, or by combining GPS, GRACE gravimetry and ocean circulation model predicted ocean bottom pressure (OBP) data. GRACE observes ocean mass variations, including the effect of glacial isostatic adjustment (GIA), but is insensitive to geocenter motion. Satellite altimetry observes the total sea level variations, which include ocean mass variations, geocenter motion, and thermo-steric or steric sea level. Here, we develop a theoretical basis for the geocenter motion, with an intent to estimate its seasonal, interannual and secular variations, and accounting for possible drift in the International Terrestrial Reference Frame (ITRF), degree one glacial isostatic adjustment effects, the associated elastic loading and Love numbers, present-day ocean mass variations. We then provide an estimate of geocenter variations, by combining GRACE, Jason-1 or ENVISAT altimetry and Argo hydrographic measurements, 20022012. We primarily use geodetic observations in favor of ocean model predicted ocean bottom pressure variations, thus better retaining the low-frequency component of the recovered geocenter variations. The effect of the degree-one terms from the GIA process and its separation from present-day mass change is considered here. We conducted accuracy assessment by comparing the geocenter solution in this study with other contemporary solutions that used different techniques. We conclude that the observation-derived geocenter solution is more accurate and more appropriate to be used to supplement GRACE observations for Earth mass redistribution studies. Finally, the estimated secular geocenter motion is compared with modeling assuming plausible present-day ice-sheet and mountain glacier rapid ablation.