Hydrological excitation of polar motion

International audienceFirst harmonics of the gravity field (C21 and S21), derived from the Gravity Recovery and Climate Experiment (GRACE), and processed at different institutes, are used to determine thehydrological equatorial excitation function of polar motion. For that purpose time-variable gravity field solutions are made tidal free and free from modelled non-tidal atmospheric and oceanic effects. The residuals reflect unmodelled variations like hydrological processes, snow cover, post-glacial rebound orpossibly earthquakes. They are compared to the hydrological excitation computed from hydrological models. They are also compared to the residual geodetic excitation after removing the atmospheric and oceanic effects. We find that seasonal variations of the excit tion computed from gravimetric data andgeodetic residuals are in good agreement. Annual signal is not well represented by hydrological models.All series show common biennial oscillations with periods of nearly 1.7 and 2.6 years