Ocean angular momentum from a recent global state estimate, with assessment of uncertainties

Earth rotation studies require accurate knowledge of the global oceanic velocity and mass fields, for proper accounting of ocean angular momentum (OAM) effects on the planetary budget. We analyse a new OAM series (1992-2015) based on the solution of a global general circulation model constrained to most existing ocean data. The impact of the data-constrained optimization on OAM is substantial, and particularly essential for calculating effects of global mean ocean mass changes, which can be important for determining annual cycles and long term trends in OAM. The contributions of sea ice to OAM variations, also estimated, are found to be negligible. Uncertainties in OAM series are assessed by comparison with other available estimates. Results indicate low signal-to-noise ratios for all the analysed OAM series. Comparisons with geodetic, atmospheric and hydrologic data, in the context of the planetary angular momentum budget, point to the continued need for improvements in some or all of the series. Possible paths are offered for producing better OAM estimates in the future.