Internal Wave Scattering in Continental Slope Canyons: A Parameter Space Study

When internal waves interact with topography, such as continental slopes, they can deposit their energy to local dissipation and diapycnal mixing. Submarine canyons comprise approximately ten percent of global continental slopes, and can enhance the local dissipation of internal wave energy, yet parameterizations of canyon mixing processes are currently missing from large-scale ocean models. As a first step in the development of such parameterizations, we conduct a parameter space study of M2 tidal-frequency, low-mode internal waves interacting with idealized V-shaped canyon topographies. Specifically, we employ a two-pronged approach: a suite of numerical simulations using the MITgcm, as well as a theoretical ray-tracing algorithm, in which we vary the mouth width and sidewall slope (i.e. flat bottom or critical slope) of the canyon. At intermediate canyon widths, we observe multiple wave reflections, leading to increased vertical wavenumber, and thus decreased Richardson number. The instability that results leads to increased dissipation. Relative to a supercritical continental slope without a canyon, we find that V-shaped flat bottom canyons always dissipate more energy and are an effective geometry for wave trapping and subsequent energy loss. When both flat bottom canyons and critical slope canyons are made narrower, less wave energy enters the canyon, but a larger fraction of that energy is lost to dissipation due to subsequent reflections and wave trapping. The relative important of convective and shear-driven instability can be deduced from examination of the Richardson. As a next step, we seek to expand this parameter-space study to realistic topographies, such as Atlantis and Veatch Canyons, in order to validate our wave reflection and dissipation theory.