Modeling and Analysis of Internal-Tide Generation and Beamlike Onshore Propagation in the Vicinity of Shelfbreak Canyons

Abstract

A hydrostatic numerical model with alongshore-uniform barotropic M 2 tidal boundary forcing and idealized shelfbreak canyon bathymetries is used to study internal-tide generation and onshore propagation. A control simulation with Mid-Atlantic Bight representative bathymetry is supported by other simulations that serve to identify specific processes. The canyons and adjacent slopes are transcritical in steepness with respect to M 2 internal wave characteristics. Although the various canyons are symmetrical in structure, barotropicto-baroclinic energy conversion rates C y are typically asymmetrical within them. The resulting onshorepropagating internal waves are the strongest along beams in the horizontal plane, with the stronger beam in the control simulation lying on the side with higher C y . Analysis of the simulation results suggests that the cross-canyon asymmetrical C y distributions are caused by multiple-scattering effects on one canyon side slope, because the phase variation in the spatially distributed internal-tide sources, governed by variations in the orientation of the bathymetry gradient vector, allows resonant internal-tide generation. A less complex, semianalytical, modal internal wave propagation model with sources placed along the critical-slope locus (where the M 2 internal wave characteristic is tangent to the seabed) and variable source phasing is used to diagnose the physics of the horizontal beams of onshore internal wave radiation. Model analysis explains how the cross-canyon phase and amplitude variations in the locally generated internal tides affect parameters of the internal-tide beams. Under the assumption that strong internal tides on continental shelves evolve to include nonlinear wave trains, the asymmetrical internal-tide generation and beam radiation effects may lead to nonlinear internal waves and enhanced mixing occurring preferentially on one side of shelfbreak canyons, in the absence of other influencing factors.

Focusing of baroclinic tidal energy in a canyon

“…The most recent model study conducted by Zhang et al . [] for an idealized and supercritical for semidiurnal M2 tide canyon confirmed an asymmetry of internal tide near the canyon, which presumably is a consequence of the alongshore effects of propagating internal tidal wave. In fact, they focus mostly on resonant effects of internal tide generation in the canyon and its beam‐like onshore propagation alongside explanation of the reasons for the asymmetry of tidal fields.…”

“…With relevance to the present study, Zhang et al . [] reported the beam‐like structure of baroclinic tides near the supercritical canyon, with a difference in deepward and shoreward structures, although their interference in the canyon area was not demonstrated.…”

“…[], and Zhang et al . []. A more realistic model set up, specifically, the real bottom topography, was taken in a further series of numerical experiments performed for Monterey Submarine Canyon area: Petruncio et al .…”

“…Some studies on the baroclinic dynamics in canyons were conducted for an idealized bottom profiles by Baines [1983], St. Laurent et al [2003], Grimshaw et al [1985], and Zhang et al [2014]. A more realistic model set up, specifically, the real bottom topography, was taken in a further series of numerical experiments performed for Monterey Submarine Canyon area: Petruncio et al [2002] used POM, Jachec et al [2006] operated with SUNTANS, andHall andCarter [2011] used POM to investigate internal tides in the canyon area.…”

Issues and progress in the prediction of ocean submesoscale features and internal waves

“…Work is underway toward two-way nesting subdomains having the scope and resolution required to effectively model internal tides and internal waves. Convergence testing related to our recently published internal-tide generation studies [36,37] suggests that 1-km horizontal resolution may provide accurate internal-tide predictions.…”