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Time variation of the European gravity field from superconducting gravimeters



Ground-based gravity observations have the potential to add useful information to the interpretation of data from the new satellite gravity missions (CHAMP, GRACE, GOCE). We examine 4.5 yr of data from eight superconducting gravimeters (SGs) associated with the Global Geodynamics Project (GGP), from 1997 to 2001, and simulate the time variations that might be seen by a satellite. Signals that are removed from the gravity data before spatial averaging are the solid Earth and ocean tides, a global atmospheric loading using a vertical perfect gas law for the atmosphere, International Earth Rotation Service (IERS) polar motion and instrument drift. The 1-d gravity residuals form the basis of an interpolated minimum curvature grid that we spatially average and analyse using both surface polynomials and empirical orthogonal functions (EOFs). A clear annual component is present that, if truly regional, should be easily detectable by a satellite such as GRACE. The signal is consistent with expected continental water storage, which provides some interest for the future comparison of ground and satellite data.

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