Variations and geophysical excitations of Earth’s dynamic oblateness estimated from GPS, OBP and GRACE

Planet Earth is a rotating flat ellipsoid and its dynamics oblateness (i.e. J2) changes were mainly driven by the redistribution of Earth’s fluid mass and interaction of various spheres in the Earth system. Currently, the dynamics oblateness was determined from the satellite laser ranging (SLR) data. However, it was subject to the sparse SLR stations, uneven distribution in the Northern and Southern Hemispheres and non-continuous observation as well as dynamic models and constants in SLR data processing. Although the new generation of satellite gravity mission GRACE (gravity recovery and climate experiment) measurement has largely improved the lower-order coefficient estimates with one or two orders of magnitude, but the C20 is not sensitive. In this paper, the high precise dynamics oblateness J2 is derived from global continuous GPS loading displacements and GPS+OBP (ocean bottom pressure) as well as GPS+OBP+GRACE, respectively, which are analyzed and compared at multi-scales variations as well as their implications. It has shown that the annual variations of J2 have a good agreement between GPS+OBP, GPS+OBP+GRACE, SLR and GRACE, while GPS alone has a smaller amplitude. For semi-annual variations, GRACE estimate is relatively worse due to the effect of about 161-day S2 tide. Also the GPS+OBP and GPS+OBP+GRACE have a good correlation with SLR in intraseasonal and interannual J2 variations, while GPS or GRACE alone is worse. Furthermore, the excitations of multi-scale J2 variations are investigated and analyzed using geophysical models data. Results show that the variations of J2 at seasonal, intraseasonal and interannual scales are mainly driven by the transfer and redistribution of Earth’s surface atmosphere, ocean and land water mass.