Assessment of GRACE Time-Variable Gravity over the Ocean
San Francisco, CA
Monthly time-varying gravity coefficients from the GRACE project are converted into equivalent water level over the ocean using various smoothing radii ranging from 300 km to 1500 km. The resulting maps are assessed both qualitatively by examining Empirical Orthogonal Functions (EOFs), and quantitatively by comparing the maps to an expected signal derived from steric-corrected altimetry. Although larger smoothing radii reduce the error in the GRACE maps, they also smooth out the signal more. We find that the largest signal-to-noise ratio occurs with a smoothing radius of 1000 km. At this level of smoothing, the Release-01 GRACE data have an error of 2 cm RMS or less.