A new assessment of long-wavelength gravitational variations

We estimate the degree 2 long-wavelength gravitational variations C-21, S-21, and C-20 using Earth rotational changes, caused by mass redistribution and movement within the Earth system. These rotation changes are accurately measured by space geodetic techniques. Wind and oceanic current effects are removed from the Earth rotation series using atmospheric and oceanic circulation data-assimilating models. The results are compared with LAGEOS Satellite Laser Ranging (SLR) determinations and also with geophysical contributions estimated from atmospheric surface pressure, continental water storage, and nonsteric sea level changes. Our conjecture is that using Earth rotational changes to infer long-wavelength gravitational variations has the potential to be more accurate than satellite-based techniques in some cases. Consistent with this, we find that C-21 and S-21 variations from this study are in better agreement with geophysical observations than LAGEOS SLR determinations of C-21 and S-21 However, the Earth rotation-derived estimate of C-20 variation is probably less accurate than the LAGEOS-derived result owing to the large atmospheric wind contribution to length-of-day variation which must first be removed and the natural sensitivity of LAGEOS to C-20 changes via precession of the satellite node.