M2-Internal-Tide Generation in a 0.1 Degree Global Simulation of Circulations and Tides with Realistic Topography

Internal-tide generation has been quantified using two different expressions, one based on the pressure work and the other on the energy conversion. So far, the link between the two has not been quantified. We show here that the two expressions are identical under the assumptions that the internal-tide pressure is hydrostatic and has a zero depth average. Based on a simulation with a 0.1 degree ocean general circulation model that resolves internal-tide generation on a realistic topography, we find that the M2 internal tide is generated by the known process characterized by a systematic pressure drop from the windward to the leeward side of an obstacle as barotropic tide impinges on the obstacle. Moreover, although the generation is affected by both the tidal velocity and the topographic slope, we find that the former plays a more dominant role than the latter. The dominance arises not only because the internal-tide generation is linear in the topographic slope but essentially quadratic in the tidal velocity, but also because the tidal velocity can change up to one order of magnitude from the top to the foot of a high ridge within a distance as short as 100 km, a feature only produced by a high-resolution model. Thus, new features regarding the location of the intense generation emerge. The intense generation maps the immediate proximities of the summits of the major high underwater ridges and rises. Summing up for a given bottom depth, the generation is strongest above 1200 m and weakens drastically below 3000 m.