ALBERT

Description: We investigate the cascade of low-mode internal tide energy from primary to supertidal frequencies in a realistically forced global Hybrid Coordinate Ocean Model (HYCOM) simulation with a 4-km horizontal resolution. Supertidal kinetic energy (KE) is elevated in low-latitude regions, where stratification is strong and rotation is weak, e.g., near the Amazon Shelf, Bay of Bengal, and Mascarene Ridge, and amounts up to 50% of the total internal tide KE several 100 km away from the generation sites. We compute time-mean and depth-integrated supertidal flux divergence and topographic barotropic to baroclinic energy conversion. The flux divergence is organized in regularly spaced banding patterns along the horizontal internal tide beams. The separation distance between the bands is larger than a semidiurnal mode 1 wavelength. The positive flux divergence of 10-50 mWm2 cannot be explained with the supertidal topographic conversion, which is negligible. Instead, it agrees with nonlinear KE transfer rates from the tidal to the supertidal band, which are computed with the novel coarse-graining approach. Both the supertidal flux divergence and nonlinear KE transfers are enhanced in patches near the surface, where KE is large. We attribute the elevated surface KE in the banding patterns to the constructive interference between semidiurnal mode 1 and mode 2 internal tides, which propagate away from the generation sites. These nonlinear KE transfers are due to triad wave-wave interactions. While this HYCOM simulation begins to resolve nonlinear energy transfers and the internal wave energy cascade, we anticipate that future higher-resolution simulations will lead to further improvements.