Oceanic tides from Earth-like to ocean planets

Abstract

Oceanic tides are a major source of tidal dissipation. They drive the evolution of planetary systems and the rotational dynamics of planets. However, 2D models commonly used for the Earth cannot be applied to extrasolar telluric planets hosting potentially deep oceans because they ignore the three-dimensional effects related to the ocean vertical structure. Our goal is to investigate in a consistant way the importance of the contribution of internal gravity waves in the oceanic tidal response and to propose a modeling allowing to treat a wide range of cases from shallow to deep oceans. A 3D ab initio model is developed to study the dynamics of a global planetary ocean. This model takes into account compressibility, stratification and sphericity terms, which are usually ignored in 2D approaches. An analytic solution is computed and used to study the dependence of the tidal response on the tidal frequency and on the ocean depth and stratification. In the 2D asymptotic limit, we recover the frequency-resonant behaviour due to surface inertial-gravity waves identified by early studies. As the ocean depth and Brunt-Väisälä frequency increase, the contribution of internal gravity waves grows in importance and the tidal response become three-dimensional. In the case of deep oceans, the stable stratification induces resonances that can increase the tidal dissipation rate by several orders of magnitude. It is thus able to affect significantly the evolution time scale of the planetary rotation.