On the Damping of Free Coastal-Trapped Waves

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  • 1 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
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Abstract

A perturbative method is presented for estimating the decay time of subinertial coastal-trapped waves under a wide range of conditions where damping is relatively weak. Bottom friction is sometimes much more important than “long-wave” results would suggest, even in the parameter range where the waves are approximately non-dispersive. The presence of a mean flow can greatly change the effect of bottom friction. Specifically, if the mean flow over the shelf has positive (negative) relative vorticity in the Northern (Southern) Hemisphere, wave damping increases. This mean flow effect appears to account for the failure of coastal-trapped waves to propagate into the Agulhas between Port Elizabeth and Durban, South Africa.

Abstract

A perturbative method is presented for estimating the decay time of subinertial coastal-trapped waves under a wide range of conditions where damping is relatively weak. Bottom friction is sometimes much more important than “long-wave” results would suggest, even in the parameter range where the waves are approximately non-dispersive. The presence of a mean flow can greatly change the effect of bottom friction. Specifically, if the mean flow over the shelf has positive (negative) relative vorticity in the Northern (Southern) Hemisphere, wave damping increases. This mean flow effect appears to account for the failure of coastal-trapped waves to propagate into the Agulhas between Port Elizabeth and Durban, South Africa.

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