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Kelvin Wave Propagation in a High Drag Coastal Environment

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  • 1 Institute Of Marine Resources, Scripps Institution of Oceanography, La Jolla, California
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Abstract

Coastally trapped Kelvin waves in a model system of a flat half-planar ocean with a high-drag region of width L adjacent to the coast have properties that depend on L, and its drag, D0. For L less than the Rossby radius, there is a Kelvin wave which has an attenuation coefficient proportional to L. The loss of energy in the drag region results in a nonzero cross-shore velocity which transports energy into the high drag region. Additional trapped waves modes are possible for larger L. At sufficiently large D0, Kelvin waves are trapped on the outer edge of the high drag region rather than at the coast. When this occurs, there is a decrease in the attenuation coefficient. Under conditions of large L and D0, there are also very heavily damped Poincaré waves trapped in the drag region. There is a Lagrangian drift at the outer edge of the high drag zone in the direction of Kelvin wave propagation when D0 is small. The Lagrangian drift can be in the opposite direction when D0 is large. Comparison with coastal kelp beds, known regions of high drag, suggest that there is no effect on the propagation of barotropic Kelvin waves but a large effect on longshore currents associated with the Kelvin wave in the drag region. There is a potentially large effect on the propagation of baroclinic Kelvin waves as well as on the pattern of their currents. Large drags associated with the interaction of surface waves and the benthos could extend the range of conditions where such effects can occur.

Abstract

Coastally trapped Kelvin waves in a model system of a flat half-planar ocean with a high-drag region of width L adjacent to the coast have properties that depend on L, and its drag, D0. For L less than the Rossby radius, there is a Kelvin wave which has an attenuation coefficient proportional to L. The loss of energy in the drag region results in a nonzero cross-shore velocity which transports energy into the high drag region. Additional trapped waves modes are possible for larger L. At sufficiently large D0, Kelvin waves are trapped on the outer edge of the high drag region rather than at the coast. When this occurs, there is a decrease in the attenuation coefficient. Under conditions of large L and D0, there are also very heavily damped Poincaré waves trapped in the drag region. There is a Lagrangian drift at the outer edge of the high drag zone in the direction of Kelvin wave propagation when D0 is small. The Lagrangian drift can be in the opposite direction when D0 is large. Comparison with coastal kelp beds, known regions of high drag, suggest that there is no effect on the propagation of barotropic Kelvin waves but a large effect on longshore currents associated with the Kelvin wave in the drag region. There is a potentially large effect on the propagation of baroclinic Kelvin waves as well as on the pattern of their currents. Large drags associated with the interaction of surface waves and the benthos could extend the range of conditions where such effects can occur.

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