High-frequency Earth rotation variations deduced from altimetry-based ocean tides: Fid-Bau Portal

High-frequency Earth rotation variations deduced from altimetry-based ocean tides

Madzak, Matthias / Schindelegger, Michael / Böhm, Johannes / Bosch, Wolfgang / Hagedoorn, Jan

Abstract A model of diurnal and semi-diurnal variations in Earth rotation parameters (ERP) is constructed based on altimetry-measured tidal heights from a multi-mission empirical ocean tide solution. Barotropic currents contributing to relative angular momentum changes are estimated for nine major tides in a global inversion algorithm that solves the two-dimensional momentum equations on a regular 0.5$$^\circ $$ grid with a heavily weighted continuity constraint. The influence of 19 minor tides is accounted for by linear admittance interpolation of ocean tidal angular momentum, although the assumption of smooth admittance variations with frequency appears to be a doubtful concept for semi-diurnal mass terms in particular. A validation of the newly derived model based on post-fit corrections to polar motion and universal time ($$\Delta $$UT1) from the analysis of Very Long Baseline Interferometry (VLBI) observations shows a variance reduction for semi-diurnal $$\Delta $$UT1 residuals that is significant at the 0.05 level with respect to the conventional ERP model. Improvements are also evident for the explicitly modeled K$$_1$$, Q$$_1$$, and K$$_2$$ tides in individual ERP components, but large residuals of more than 15 $$\mu $$as remain at the principal lunar frequencies of O$$_1$$ and M$$_2$$. We attribute these shortcomings to uncertainties in the inverted relative angular momentum changes and, to a minor extent, to violation of mass conservation in the empirical ocean tide solution. Further dedicated hydrodynamic modeling efforts of these anomalous constituents are required to meet the accuracy standards of modern space geodesy.