Model Estimates of M2 Internal Tide Generation over Mid-Atlantic Ridge Topography

Abstract

The conversion of barotropic to baroclinic M2 tidal energy is examined for a section of the Mid-Atlantic Ridge in the Brazil Basin using a primitive equation model. Model runs are made with different horizontal smoothing (1.5, 6, and 15 km) applied to a 192 km ? 183 km section of multibeam bathymetry to characterize the influence of topographic resolution on the model conversion rates. In all model simulations, barotropic to baroclinic conversion is highest over near- and supercritical slopes on the flanks of abyssal hills and discordant zones. From these generation sites, internal tides propagate upward and downward as tidal beams. The most energetic internal tide mode generated is mode 2, consistent with the dominant length scales of the topographic slope spectrum (50 km). The topographic smoothing significantly affects the model conversion amplitudes, with the domain-averaged conversion rate from the 1.5-km run (15.1 mW m?2) 4% and 19% higher than for the 6-km (14.5 mW m?2) and 15-km runs (12.2 mW m?2), respectively. Analytical models for internal tide generation by subcritical topography predict conversion rates with modal dependence and spatial patterns qualitatively similar to the Princeton Ocean Model (POM) and also show a decrease in conversion with smoother topography. The POM conversion rates are approximately 20% higher than the analytical estimates for all model grids, which is attributed to spatial variations in the barotropic flow and near-bottom stratification over generation sites, which are incorporated in the model but not in the analytical estimates.