Investigation of low-degree gravitational changes from GRACE, Earth rotation, climate models, and satellite laser ranging

We compare several independent time series of variations C21, S21, and C20 in Earth's gravity field for the period April 2002 to May 2007, including estimates from the Gravity Recovery and Climate Experiment (GRACE), Earth rotation variations, climate models (including atmospheric, oceanic, and hydrological models), and satellite laser ranging (SLR). Recently released GRACE release 04 (RL04) solutions show significant improvement relative to earlier results, especially for C21 and S21. 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 C21 and S21, and SLR values for C20 agree best with GRACE estimates. GRACE RL04 C20 time series are still contaminated by aliased ocean tide model errors. These independent estimates of C21, S21, and C20 variations are important for validating different geodetic techniques and improving the accuracy of low-degree gravity change.