The geography of semidiurnal mode-1 internal-tide energy loss

The semidiurnal mode-1 internal tide receives 0.1-0.3 TW from the surface tide and is capable of propagating across ocean basins. The ultimate fate of mode-1 energy after long-distance propagation is poorly constrained by existing observations and numerical simulations. Here, global results from a two-dimensional semi-analytical model indicate that topographic scattering is inefficient at most locations deeper than 2500 m. Next, results from a one-dimensional linear model with realistic topography and stratification create a map of mode-1 scattering coefficients along the continental margins. On average, mode-1 internal tides lose about 60% of their energy upon impacting the continental margins: 20% transmits onto the continental shelf, 40% scatters to higher modes, and 40% reflects back to the ocean interior. These analyses indicate that the majority of mode-1 energy is likely lost at large topographic features (e.g., continental slopes, seamounts, and mid-ocean ridges), where it may drive elevated turbulent mixing. Key Points About 10% of mode-1 tide energy is lost in the ocean basins below 2500 m depth 2/3 of mode-1 tide energy is lost during reflection at the continental margins Mode-1 energy losses during reflection at oblique and normal angles are similar