Data-Unconstrained Modeling and Detection of 9 Individual Partial Ocean Tides of Third-Degree by Terrestrial Gravimetry

<p>The Tide-Generating Potential (TGP) of the Moon is not symmetric but asymmetric with respect to the Lunar sub-orbital axis due to its relative proximity compared to astronomical length scales. This asymmetry can be described in the first order by the third-degree of the TGP expanded in Spherical Harmonic functions. Despite the tiny magnitude of this asymmetry (1/60 of the leading, second degree) several corresponding oceanic partial tides were previously detected in both tide gauge and superconducting gravimeter records. </p><p><br>In this contribution, we present solutions with the data-unconstrained ocean tide model TiME (Sulzbach et al. 2021) for a number of partial tides of the third degree in all relevant tidal bands (long-period to terdiurnal). Tuning the model with the recently compiled TICON-td tide gauge dataset, we find the modelled ocean tide signals to agree at levels over 50 % with oceanographic data. The gravimetric impact of the oceanic load tides on 16 globally distributed gravimeter stations which amounts to only a few nGal is then modelled by 2 approaches: (1) a computation with SPOTL and (2) with an approach constrained by load Love numbers. While the gravity constituents modeled with both approaches are close to identical, comparison to the analysed constituents shows a high agreement between 63% to 80% for the degree-3 components depending on the selected partial tide solution, thereby confirming both the low noise level of state-of-the-art superconducting gravimeter recordings and the applied hydrodynamic modelling. </p><p><br>By modeling and analyzing for additional degree-3 constituents (resulting in three partial tides in the diurnal, semidiurnal and terdiurnal band), load tide admittance functions of degree-3 can be calculated. We show that third-degree ocean and load tides exhibit a considerable admittance-dispersion that should be considered when estimating load tide contributions of other third-degree partial tides. For example, a larger number of degree-3 tides can be considered for satellite gravity when combining the presented solutions with a linear admittance approach, which might become relevant already for the upcoming MCM/MAGIC constellation currently studied by NASA and ESA.</p><p>References:<br>[1] Sulzbach, R., Dobslaw, H., & Thomas, M. (2021), JGR: Oceans., 126, 1–21, https://doi.org/10.1029/2020JC017097</p>