Hydrological excitations of polar motion, 1993-2002

Changes in continental water storage obtained from an advanced land data assimilation system (LDAS) are employed to compute hydrological excitations of polar motion for the 10-yr period of 1993-2002. The results are compared with observed excitations of polar motion and contributions from the atmosphere and ocean, and with results from previous studies. There is remarkably good agreement between LDAS-derived results and remaining observed excitations, i.e. after atmospheric and oceanic effects are removed from the observations. LDAS-predicted hydrological excitations play a major role in closing the excitation budget for prograde and retrograde annual wobble, especially for the prograde component, and show considerably better agreement with observations than previous results. LDAS-predicted results show significantly larger interannual variability and also agree well with observed excitations not accounted for by the atmosphere and ocean. As demonstrated in this study, LDAS shows major improvement in modelling large-scale change in land water storage at both seasonal and interannual timescales.