Impact of Minor Ocean Tides on Surface Deformations and the Earth’s Gravity Field

Ocean tides are small, periodic disturbances of the ocean state variables with frequencies related to the solar and lunar ephemerides. Most prominently, they are observed at the coasts by tide gauge measurements, where variations of the free sea surface height are visible even to the bare eye. On the other hand, tide gauges are just one geodetic technique that can identify ocean tide signatures. Especially satellite altimetry is considered the critical technology for constructing highly accurate data-constrained ocean tide atlases. However, the number of frequencies available from such atlases is limited by the signal-to-noise ratio of those observations, so not all tidal lines are readily available. To account for unresolved minor ocean tides, linear admittance approaches are utilized. On the other hand, unconstrained hydrodynamic ocean tide modeling with TiME (Sulzbach et al., 2021, 2022) allows us to calculate the oceanic response for any given tidal line explicitly.

Due to the long-wavelength character of ocean tidal loading, its geophysical fingerprint is not restricted to the oceans but extends horizontally (causing deformations of the crust to which instruments are attached) and vertically (causing periodic changes in gravity at orbital heights of in particular low-Earth orbiting satellites). Thus, tidal loading systematically disturbs both satellite orbits and also geodetic observations from ground stations with SLR, GNSS, and DORIS.

In this contribution, we compare tidal predictions from different ocean tide atlases. In addition to available Stokes coefficients of the gravity potential, we calculate vertical and horizontal displacements for 34 partial tide solutions from FES14, 17 from EOT20, and 57 from the data-unconstrained model TiME based on a spherical harmonic decomposition of maximum degree 4999. We focus on the influence of minor ocean tide solutions on the tidal predictions either drawn from the broadband TiME22-catalog or derived with the help of linear admittance from EOT20/FES14 major tides. The results are validated with time series of selected geodetic measurement systems to quantify the influence of the minor tide treatment on their residuals to motivate further efforts to reduce ocean tide residuals in precise orbit determination.