Interannual variability of low-degree gravitational change, 1980?2002

Abstract

Time variations in the Earth's gravity field at periods longer than 1 year, for degree-two spherical harmonics, DC21, DS21, and DC20, are estimated from accurately measured Earth rotational variations. These are compared with predictions of atmospheric, oceanic, and hydrologic models, and with independent satellite laser ranging (SLR) results. There is remarkably good agreement between Earth rotation and model predic- tions of DC21 and DS21 over a 22-year period. After decadal signals are removed, Earth-rotation-derived interannual DC20 variations are dominated by a strong oscillation of period about 5.6 years, probably due to uncertainties in wind and ocean current estimates. The model-predicted DC20 agrees reasonably well with SLR observations during the 22-year period, with the excep- tion of the recent anomaly since 1997/1998.