Low degree gravity changes from GRACE, Earth rotation, geophysical models, and satellite laser ranging

Several independent time series of variations Delta C-21, Delta S-21, and Delta C-20 in Earth's gravity field are compared for the period April 2002 to May 2007. We examine estimates from the Gravity Recovery and Climate Experiment (GRACE), Earth rotation variations, climate models, and satellite laser ranging (SLR). Recently released GRACE solutions show significant improvement relative to earlier results, especially for Delta C-21 and Delta S-21. At the annual period, all estimates agree remarkably well, and good correlation is found among time series at intraseasonal periods. In general, Earth rotation values for Delta C-21 and Delta S-21, and SLR values for Delta C-20 agree best with GRACE estimates. GRACE Delta C-20 time series are contaminated by aliased ocean tide model errors. SLR Delta C-21 and Delta S-21 time series have been reported without an ocean pole tide (OPT) correction and with an older Solid Earth Pole Tide (SEPT) model. After correcting for OPT and SEPT deficiencies, SLR Delta C-21 and Delta S-21 time series show improved agreement with other estimates.