Internal Tides Generated on a Corrugated Continental Slope. Part II: Along-Slope Barotropic Forcing

Sonya Legg Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts

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Abstract

Recent measurements in a region of continental slope characterized by ridges and valleys running up and down the slope reveal interesting high mode structure in the tidal band velocity signals, with enhanced mixing above the corrugations. In order to understand these observations, numerical simulations of the internal tide generation in this region of topography were performed. Here the focus is on the response of the flow to along;chslope barotropic tidal forcing. For small-amplitude barotropic forcing, internal waves are generated over the continental slope that propagate toward the ocean surface and toward shallower water. When higher-amplitude forcing is combined with large-amplitude corrugations, the flow is locally supercritical downstream of ridges, and transient internal hydraulic jumps result. As the flow relaxes each half tidal period, these jumps are released as internal wave packets, which propagate up into the thermocline. The internal hydraulic jumps are a source of mixing in the valleys, while the small-scale shears associated with the internal waves could lead to mixing higher up the water column. Over the forcing range considered, the response is dominated by slightly higher harmonics of the tidal forcing frequency than predicted by existing analytic theories.

Corresponding author address: Dr. Sonya Legg, Department of Physical Oceanography, Woods Hole Oceanographic Institution, MS 21, 360 Woods Hole Road, Woods Hole, MA 02543. Email: slegg@whoi.edu

Abstract

Recent measurements in a region of continental slope characterized by ridges and valleys running up and down the slope reveal interesting high mode structure in the tidal band velocity signals, with enhanced mixing above the corrugations. In order to understand these observations, numerical simulations of the internal tide generation in this region of topography were performed. Here the focus is on the response of the flow to along;chslope barotropic tidal forcing. For small-amplitude barotropic forcing, internal waves are generated over the continental slope that propagate toward the ocean surface and toward shallower water. When higher-amplitude forcing is combined with large-amplitude corrugations, the flow is locally supercritical downstream of ridges, and transient internal hydraulic jumps result. As the flow relaxes each half tidal period, these jumps are released as internal wave packets, which propagate up into the thermocline. The internal hydraulic jumps are a source of mixing in the valleys, while the small-scale shears associated with the internal waves could lead to mixing higher up the water column. Over the forcing range considered, the response is dominated by slightly higher harmonics of the tidal forcing frequency than predicted by existing analytic theories.

Corresponding author address: Dr. Sonya Legg, Department of Physical Oceanography, Woods Hole Oceanographic Institution, MS 21, 360 Woods Hole Road, Woods Hole, MA 02543. Email: slegg@whoi.edu

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