Agreement between Earth's rotation and mass displacement as detected by GRACE

The progress in GRACE data processing should improve the estimation of low degree spherical harmonics which are expected to agree better with Earth's rotation observations. The polar motion and length-of-day excitations determined from the spherical harmonics of the GRGS latest release (RL02) are explored and compared to the previous release (RL01). The RL02 gives best fit of the observed annual variations than RL01 and geophysical models do. However, the observed residual signal obtained after removing annual and semiannual oscillations is still better explained by the geophysical models even if RL02 estimates are improved at these frequencies scales. Linear trends are also estimated over study period (2003–2008). The linear trends of χ1 based on GRACE RL01/02 and EOP are similar but they are very different for χ2. Further studies with longer time series of GRACE and future gravimetric missions could help better interpret the long term variations and the effects of ice sheet mass loss or post glacial rebound. Concerning LOD variations, GRACE/LAGEOS mass displacement information brings better agreement with EOP observations, compared to the pressure term estimated by models, however the RL02 has not shown significant improvement.

► Mass change derived by gravity field and Earth rotation observations is determined. ► Latest gravity field solutions of CNES/GRGS are used. ► Progress in GRACE data processing improves the low degree gravitational estimates. ► Polar motion and LOD excitations using low degree spherical harmonics are computed. ► A good agreement is reached between gravity field measurements and EOP.