Assessment of Degree-2 Zonal Gravitational Changes from GRACE, Earth Rotation, Climate Models, and Satellite Laser Ranging

Abstract

Four independent time series of degree-2 zonal gravitational variations ΔC20 are compared for the period April 2002 to February 2008. We examine estimates from the Gravity Recovery and Climate Experiment (GRACE), Earth rotation variations, climate models (AOW), and satellite laser ranging (SLR). At the annual period, all ΔC20 estimates agree remarkably well, and good correlation is found among these time series at nonseasonal time scales as well. SLR and AOW ΔC20 time series show the best agreement in a broad band of frequencies with the maximum cross-correlation coefficient of 0.86 at nonseasonal time scales. GRACE monthly ΔC20 estimates are subject to significant aliasing effects due to errors in high-frequency tide models, especially the S2 and K2 tides. Correctly removing winds and ocean currents and other motion related excitations from length-of-day (LOD) observations plays a key role in estimating ΔC20 from LOD, especially at interannual or longer time scales. © Springer-Verlag Berlin Heidelberg 2010.