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Internal tide transformation across a continental slope off Cape Sines, Portugal
Small, J. (2002). Internal tide transformation across a continental slope off Cape Sines, Portugal, in: Frankignoulle, M. (Ed.) Exchange Processes at the Ocean Margins. Selected papers from the 32nd International Liège Colloquium on Ocean Hydrodynamics, held in Liège, Belgium on May 8-12, 2000. Journal of Marine Systems, 32(Special Issue 1-3): pp. 43-69. hdl.handle.net/10.1016/S0924-7963(02)00029-5
In: Frankignoulle, M. (Ed.) (2002). Exchange Processes at the Ocean Margins. Selected papers from the 32nd International Liège Colloquium on Ocean Hydrodynamics, held in Liège, Belgium on May 8-12, 2000. Journal of Marine Systems, 32(Special Issue 1-3). Elsevier: Amsterdam. 1-252 pp., more
In: Journal of Marine Systems. Elsevier: Tokyo; Oxford; New York; Amsterdam. ISSN 0924-7963, more
Peer reviewed article  

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Keywords
    Internal tides; Internal waves; Nonlinear wave interactions; Solitary waves; Synthetic aperture radar; ANE, Portugal [Marine Regions]; Portugal [Marine Regions]; Marine

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  • Small, J., correspondent

Abstract
    During the INTIFANTE 99 experiment in July 1999, observations were made of a prominent internal undular bore off Cape Sines, Portugal. The feature was always present and dominant in a collection of synthetic aperture radar (SAR) images of the area covering the period before, during and after the trial. During the trial, rapid dissemination of SAR data to the survey ship enabled assessment of the progression of the feature, and the consequent planning of a survey of the bore coincident with a new SAR image. Large amplitude internal waves of 50 m amplitude in 250 m water depth, and 40 m in 100 m depth, were observed. The images show that the position of the feature is linked to the phase of the tide, suggesting an internal tide origin. The individual packets of internal waves contain up to seven waves with wavelengths in the range of 500-1500 m, and successive packets are separated by internal tide distances of typically 16-20 km, suggesting phase speeds of 0.35-0.45 m s-1. The internal waves were coherent over crest lengths of between 15 and 70 km, the longer wavefronts being due to the merging of packets. This paper uses the SAR data to detail the transformation of the wave packet as it passes across the continental slope and approaches the coast. The generation sites for the feature are discussed and reasons for its unusually large amplitude are hypothesised. It is concluded that generation at critical slopes of the bathymetry and non-linear interactions are the likely explanations for the large amplitudes.

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