Non-tidal oceanic contribution to polar wobble estimated from two oceanic assimilation data sets

Contributions of ocean bottom pressure and oceanic current to polar wobble are evaluated by using two oceanic data assimilation products. One product comes from Scripps Institution of Oceanography (ECCO), and the other is the Simple Ocean Data Assimilation (SODA) developed at University of Maryland. The results show that seasonal fluctuations in these two assimilated ocean angular momentum (OAM) time series agree better with each other along the Greenwich meridian than along the 90°E meridian. Furthermore, annual OAM change for ECCO is much closer to non-atmospheric residual, than that for SODA. However, annual OAM change for SODA along the Greenwich meridian compares better than that for ECCO to non-atmospheric–hydrologic residual, in which annual and semi-annual signals of land hydrologic angular momentum (LHAM) of a climate model are considered. At the meantime, annual LHAM signals along the 90°E meridian derived from the climate model and from the GRACE data are also compatible with each other. It is likely that ECCO overestimates the annual change along the 90°E meridian according to the angular momentum conservation law in the Earth system. Consequently, the oceanic role in polar wobble should be further examined.