Using SAR imagery to survey internal solitary wave interactions: A case study off the Western Iberian shelf

Physical oceanography is increasingly relying on satellite remote sensing to survey the perpetually undersampled ocean, whereas the latest Synthetic Aperture Radars (SARs) are moving forward to provide a more continuous monitoring of the ocean. In this study we use a collection of SAR images to document the two-dimensional horizontal structure of Internal Solitary Waves (ISWs) propagating between two large submarine canyons off the Western Iberian Peninsula (between May and October 2018), which are observed to intersect approximately along the mid-shelf and originate a naturally-occurring interaction hotspot between different ISW packets. ISW interactions are well documented in theory and in laboratorial and numerical studies, but their observations in the real ocean are limited to airborne observations over the Strait of Georgia. The frequent SAR imagery of interacting ISWs in this region provides additional case studies to the literature, and we investigate if an energy proxy taken from their sea surface signatures can be used as an indicator for high-energy interaction events (e.g. when comparing with a non-interacting background). In particular, a quasi-synergetic event captured both in SAR and in a moored thermistor chain reveals that the often used weakly nonlinear theory for small-amplitude waves may underestimate the amplitudes measured in the waves? interacting sections. ISWs provide the largest vertical displacements and velocities in the ocean. Understating how their vertical structure changes during wave-wave interactions may have important implications in the broader spectrum of ocean sciences, and SARs are shown in this study to be a first-approach tool to survey this frequent phenomenon in coastal regions.

Automated summary

Physical oceanography increasingly uses satellite remote sensing to survey the under-sampled ocean, with the latest Synthetic Aperture Radars (SARs) providing continuous monitoring. This study documents the horizontal structure of Internal Solitary Waves (ISWs) between two submarine canyons off the Western Iberian Peninsula using SAR images. The study investigates using a sea surface energy proxy as an indicator for high-energy ISW interaction events, and highlights the importance of understanding ISW vertical structure changes during wave-wave interactions in coastal regions.