A new assessment of long-wavelength gravitational variations

We estimate the degree 2 long-wavelength gravitational variations C-21, S-2 1, and C-20 using Earth rotational changes, caused by mass redistribution a nd 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 circu lation data-assimilating models. The results are compared with LAGEOS Satel lite Laser Ranging (SLR) determinations and also with geophysical contribut ions estimated from atmospheric surface pressure, continental water storage , and nonsteric sea level changes. Our conjecture is that using Earth rotat ional changes to infer long-wavelength gravitational variations has the pot ential to be more accurate than satellite-based techniques in some cases. C onsistent with this, we find that C-21 and S-21 variations from this study are in better agreement with geophysical observations than LAGEOS SLR deter minations 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 owi ng to the large atmospheric wind contribution to length-of-day variation wh ich must first be removed and the natural sensitivity of LAGEOS to C-20 cha nges via precession of the satellite node.