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On the generation and propagation of internal solitary waves in the southern Bay of Biscay

On the generation and propagation of internal solitary waves in the southern Bay of Biscay
On the generation and propagation of internal solitary waves in the southern Bay of Biscay
Internal solitary waves (ISWs), travelling towards the South–South-West (SSW), are now well documented in the northern and central Bay of Biscay. These are formed from large-amplitude internal tides which result from the interaction of the barotropic tide with the steep shelf-break topography. In the present paper, we investigate available satellite imagery (Synthetic Aperture Radar (SAR) and ASAR data) to reveal that the southern Bay of Biscay is also a ‘‘hotspot’’ region which has a high level of ISW activity. Here, the ISWs travel towards the East–North-East from the Cape Finisterre region off North-West Spain. In fact, we reveal the presence of two wave-trains travelling in slightly different directions (0551T and 0401T). By calculating the strength of the barotropic tidal forcing in the region, and identifying the likely propagation pathways (rays) of internal tidal (IT) energy, we identify the generation sites for these wave-trains as lying on either side of the Ortegal Promontory (OP). This is an undersea ‘‘headland’’ projecting towards the North-West from the north-western coast of Spain (near 441N, 8.51W), and over which the barotropic tides are forced to flow. For each generation site, IT rays emanating from ‘‘critical’’ topography (where the ray slope is equal to the topographic slope) in regions of strong barotropic forcing, rise to the surface (for one site after a reflection from the sea-floor) and pass through the thermocline close to the earliest occurrences of the ISWs in the respective wave trains. These rays would then produce, through nonlinear processes, the ISWs through the same ‘‘local generation’’ mechanism that has been used to explain the occurrence of the ISWs in the northern and central Bay. The ‘‘local generation’’ mechanism may therefore be more widely applicable than previously thought. In addition, the methods we have used to deduce the generation sites for these waves are expected to prove equally useful for studies in other areas of the world’s oceans.
internal solitary waves, internal tides, Synthetic Aperture Radar, Bay of Biscay
0967-0637
927-941
Azevedo, A.
490d5681-20b8-41b1-b9e9-105e7bed672b
da Silva, J.C.B.
f0299437-57df-41b7-a0fd-520aa8d0a319
New, A.L.
69c2be8b-c6c2-408f-9612-6980b1a25802
Azevedo, A.
490d5681-20b8-41b1-b9e9-105e7bed672b
da Silva, J.C.B.
f0299437-57df-41b7-a0fd-520aa8d0a319
New, A.L.
69c2be8b-c6c2-408f-9612-6980b1a25802

Azevedo, A., da Silva, J.C.B. and New, A.L. (2006) On the generation and propagation of internal solitary waves in the southern Bay of Biscay. Deep Sea Research Part I: Oceanographic Research Papers, 53 (6), 927-941. (doi:10.1016/j.dsr.2006.01.013).

Record type: Article

Abstract

Internal solitary waves (ISWs), travelling towards the South–South-West (SSW), are now well documented in the northern and central Bay of Biscay. These are formed from large-amplitude internal tides which result from the interaction of the barotropic tide with the steep shelf-break topography. In the present paper, we investigate available satellite imagery (Synthetic Aperture Radar (SAR) and ASAR data) to reveal that the southern Bay of Biscay is also a ‘‘hotspot’’ region which has a high level of ISW activity. Here, the ISWs travel towards the East–North-East from the Cape Finisterre region off North-West Spain. In fact, we reveal the presence of two wave-trains travelling in slightly different directions (0551T and 0401T). By calculating the strength of the barotropic tidal forcing in the region, and identifying the likely propagation pathways (rays) of internal tidal (IT) energy, we identify the generation sites for these wave-trains as lying on either side of the Ortegal Promontory (OP). This is an undersea ‘‘headland’’ projecting towards the North-West from the north-western coast of Spain (near 441N, 8.51W), and over which the barotropic tides are forced to flow. For each generation site, IT rays emanating from ‘‘critical’’ topography (where the ray slope is equal to the topographic slope) in regions of strong barotropic forcing, rise to the surface (for one site after a reflection from the sea-floor) and pass through the thermocline close to the earliest occurrences of the ISWs in the respective wave trains. These rays would then produce, through nonlinear processes, the ISWs through the same ‘‘local generation’’ mechanism that has been used to explain the occurrence of the ISWs in the northern and central Bay. The ‘‘local generation’’ mechanism may therefore be more widely applicable than previously thought. In addition, the methods we have used to deduce the generation sites for these waves are expected to prove equally useful for studies in other areas of the world’s oceans.

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Published date: 2006
Keywords: internal solitary waves, internal tides, Synthetic Aperture Radar, Bay of Biscay

Identifiers

Local EPrints ID: 41250
URI: https://eprints.soton.ac.uk/id/eprint/41250
ISSN: 0967-0637
PURE UUID: 17db2596-c03a-45f6-83c0-f9bf56dbe6a5

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Date deposited: 09 Aug 2006
Last modified: 17 Jul 2017 15:31

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Contributors

Author: A. Azevedo
Author: J.C.B. da Silva
Author: A.L. New

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