Improving ocean angular momentum estimates using a model constrained by data

Ocean angular momentum (OAM) calculations using forward model runs without any data, constraints have recently revealed the effects of OAM variability on the Earth's rotation. Here we use an ocean model and its adjoint to est imate OAM values bg constraining the model to available oceanic data. The o ptimization procedure yields substantial changes in OAM, related to adjustm ents in both motion and mass fields. as well as in the wind stress torques acting on the ocean. Constrained and unconstrained OAM values are discussed in the contest of closing the planet's angular momentum budget. The estima tion procedure yields noticeable improvements in the agreement with the obs erved Earth rotation parameters, particularly at the seasonal timescale. Th e comparison with Earth rotation measurements provides an independent consi stency check on the estimated ocean state and underlines the importance of ocean state estimation for quantitative studies of the variable large-scale oceanic mass and circulation fields, including studies of OAM.