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Weifeng (Gordon) Zhang, Woods Hole Oceanographic Institution, US
Timothy F. Duda, Woods Hole Oceanographic Institution, US
Inhomogeneous internal wave generation and propagation at a shelfbreak canyon

This study focuses on the tidal generation of internal waves at a shelfbreak canyon and the subsequent wave evolution around the canyon. Hydrodynamic models with idealized (but typical) canyon bathymetries and forced by a barotropic (surface) tide are used to simulate the internal wave generation and propagation processes. Model simulations show that the forcing of internal waves by barotropic tides is strongly asymmetrical with respect to the canyon axis even though the canyons are symmetrical in structure. This leads to internal waves of much larger amplitude on one canyon side-slope than the other. The resulting onshore-propagating internal waves are strongest along beams in the horizontal plane, with the stronger beam lying on the side with higher energy conversion. Analysis of the simulation results suggests that multiple-scattering effects on one canyon side-slope cause the cross-canyon asymmetrical energy conversion. As opposed to a single-scatter model where the conversion of surface tide energy to internal waves depends only on the surface tides, the multiple-scatter model allows the internal waves to affect the conversion process (feedback). Essentially, the phase variation in the spatially distributed collection of internal-wave sources, governed by variations in the orientation of the bathymetry gradient vector, allows resonant internal-wave generation on one canyon side-slope, but not the other. The cross-canyon phase variations of the internal wave sources also cause phased array-like behavior, forming the internal wave radiation beam and leads to localized formation of high-frequency solitary internal waves. Presumably, the asymmetrical internal wave generation leads to water mixing occurring preferentially on one side of canyons, which may have important biological implications. The asymmetrical internal wave generation can also induce inhomogeneous sediment transport within the canyon through the localized strong near-bottom oscillatory flows. Results of this modeling work call for more dedicated field studies of circulation and internal wave processes in shelfbreak canyons.

Theme 1: Canyon processes in the space-time continuum (formation, evolution, circulation)
Oral Presentation
internal wave, tide, asymmetry, mixing