Experiments on waves trapped over the continental slope and shelf in a continuously stratified rotating ocean, and their incidence on a canyon
Abstract:Continental margins form a waveguide for topographic Rossby waves, which can be trapped to the bottom by continuous stratification and concentrated over the continental slope while propagating along the coast. We present results of laboratory wave simulations designed to keep as many dimensionless numbers (Rossby, Burger, normalized frequency, wave steepness, geometrical, Ekman, and Reynolds) as possible similar to those of coastal-trapped waves, such as are observed in coastal regions around the world. The 13-m diameter rotating tank is salt-stratified and a continental slope joins a shallow shelf region along the outer tank circumference to a deep central region. The velocity field is measured using a correlation-based digital particle image velocimetry technique at several depths. Current ellipses downstream from subinertial forcing indicate along-isobath propagation with energy concentrated at depth and three-dimensional structure in agreement with a numerical wave solution calculated using the experimental geometry, rotation rate, and buoyancy frequency. Contrasting the inviscid wave solution, experimental flow shows an asymmetry with positive time-mean uv correlations (u across isobaths toward deep water, v along isobaths with shallow water to the left), and phase variations perpendicular to isobaths with flow near the shelf break leading that farther inshore and offshore. Both of these attributes have been seen previously in ocean observations and are interpreted as the signature of frictional influences based on stratified slope-Kelvin wave behavior. When incident on a canyon that indents the slope and shelf, a wave propagates in to and out of it along isobaths while remaining concentrated over the sloping topography with only weakly modified amplitude and phase structure. Based on the limited range of parameter space studied, the implication is that alongshore wave propagation will remain largely unmodified by natural corrugations in the slope and shelf and loss of energy by scattering will be weak.
Document Type: Research Article
Publication date: July 1, 1999
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