On the role of SAR for observing "local generation" of internal solitary waves off the Iberian Peninsula

Abstract

Internal tides are well known to result from the interaction of the surface tide with steep sea-floor or shelf-break topography. Large-amplitude internal solitary waves (ISWs) have been observed occurring in packets in open ocean areas well away from such pronounced topography. The Bay of Biscay is a region where these waves could be generated "locally" by the reflection or scattering of an internal tidal beam from the near-surface thermocline. In this paper we investigate available ENVISAT ASAR and ERS SAR imagery to study the generation of ISWs in the southern Bay of Biscay (43–45°N, 7–10°W) and off the southwest Iberian Peninsula (37–39°N, 8.5–10.5°W). In the southern Bay of Biscay, image analyses have shown the presence of packets of ISWs propagating towards the north-northwest (in addition to the previously observed ISWs propagating towards the east-northeast) from the Cape Ortegal region off the northwest Iberian Peninsula. Furthermore, the imagery revealed, for the first time, evidence of "local generation" of ISWs off southwest Portugal, travelling both offshore (two sets of waves, generated after reflections of internal tidal rays from the sea floor) and onshore (one example, generated directly by an upward ray without a bottom reflection).