Near-resonant generation of internal tide superharmonics: comparing theoretical predictions with a global ocean model

Internal tides are generated in the stratified ocean interior by the interaction of barotropic tidal currents with rough bathymetry. Low-vertical-mode internal tides can transport energy far from their generation site, but it remains unclear how and where this energy is eventually dissipated at small scales. A potential mechanism for the transfer of energy from low-mode internal tides to smaller scales in equatorial regions is superharmonic generation, whereby nonlinear self-interaction of internal tides in non-uniform stratification excites waves with shorter wavelengths and higher frequencies. Here, we use a realistically-forced global configuration of the Massachusetts Institute of Technology general circulation model to investigate an enhanced superharmonic signal in the equatorial Pacific Ocean. Using existing theory, we demonstrate that the superharmonic amplitude is consistent with nonlinear self-interaction of the original baroclinic tide, providing strong evidence for an energy pathway from the mode-1 semidiurnal internal tide to smaller horizontal scales.