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, ΔC₂₁, ΔS₂₁, and ΔC₂₀, 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 predictions of ΔC₂₁ and ΔS₂₁ over a 22-year period. After decadal signals are removed, Earth-rotation-derived interannual ΔC₂₀ 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 ΔC₂₀ agrees reasonably well with SLR observations during the 22-year period, with the exception of the recent anomaly since 1997/1998.