Evaluating predicted diurnal and semidiurnal tidal variations in polar motion with GPS‐based observations

Abstract

AbstractWe evaluate models for the predicted diurnal and semidiurnal tidal variations in polar motion using observations based upon the Global Positioning System (GPS). The GPS‐based observations are composed of 10 year continuous time series of polar motion estimates with 15 min temporal resolution. Predicted effects account for the contributions from ocean tide angular momentum and libration. We consider two models for the predicted ocean tide effects, both of which have their heritage with the so‐called TPXO hydrodynamic models of the ocean tide heights and currents that assimilate satellite altimetry, for example, Egbert et al. (1994) and Egbert and Erofeeva (2002). When considering libration effects we use the model from Mathews and Bretagnon (2003). Of the models considered in this study, the best consistency with the GPS‐based observations is achieved with predictions from the most recent (version 8) TPXO‐based model for ocean tide effects together with the model for libration effects. This combination demonstrates closure of the budget between predicted and GPS‐based observations at the level of less than 10, 2, and 5 µas in prograde diurnal, prograde semidiurnal, and retrograde semidiurnal tidal variations in polar motion, respectively. The observations also demonstrate inconsistency between the older TPXO‐based model for ocean tide effects and the libration model, both of which are currently recommended by the International Earth Rotation Service.