Unconstrained global simulations of ocean tides up to degree 3 for satellite gravimetry

Tidal de-aliasing of satellite gravimetric data is a critical task in order to correctly extract gravimetric signatures of climate signals like glacier melting or groundwater depletion and poses a high demand on the accuracy of the employed tidal solutions (Flechtner et al., 2016). Modern tidal atlases that are constrained by altimetry data possess a high level of accuracy, especially for partial tides exhibiting large open ocean signals (e.g. M2, K1). Since the achievable precision directly depends on the available density and quality of altimetry data, the accuracy relative to the tidal amplitude drops for minor tidal excitations (worse signal-to-noise ratio) as well as in polar latitudes (sparse satellite-data). In contrast, this drop in relative accuracy can be reduced by employing an unconstrained tidal model acting independently of altimetric data.
We will present recent results from the purely-hydrodynamic, barotropic tidal model TiME (Weis et al., 2008) that benefit from a set of recently implemented upgrades. Among others, these include a revised scheme for dynamic feedbacks of self-attraction and loading; energy-dissipation by parametrized internal wavedrag; partial tide excitations by the tide-generating potential up to degree 3; and a pole-rotation scheme allowing for simulations dedicated to polar areas. Benefiting from the recent updates, the obtained solutions for major tides are on the same level of accuracy as comparable modern unconstrained tidal models. Furthermore, we show that the relative accuracy level only drops moderately for tidal excitations with small excitation strength (e.g. for minor tides), thus narrowing down the accuracy gap to data-constrained tidal atlases. Exemplarily for this, we introduce solutions for minor tidal excitations of degrees 2 and 3 that represent valuable constraints for the expected ocean tide dynamics. While they are currently not considered for GRACE-FO de-aliasing we demonstrate that third-degree tides can lead to relevant aliasing of satellite gravity fields and correspond closely to recently published empirical solutions (Ray, 2020).