Ariane Koch-Larrouy (CECI CNRS/Cerfacs/IRD, Université de Toulouse, France); Jorge Manuel Magalhães (Interdisciplinary Centre of Marine and Environmental Research & Department of Geosciences, Environment and Spatial Planning, University of Porto (CIMAR/CIIMAR), Portugal); José Carlos Bastos da Silva (Interdisciplinary Centre of Marine and Environmental Research & Department of Geosciences, Environment and Spatial Planning, University of Porto (CIMAR/CIIMAR), Portugal); Fabius Kouogang (CECI, Université de Toulouse, CERFACS/CNRS/IRD ; Departamento de Oceanografia, Universidade Federal de Pernambuco (DOCEAN/UFPE), France / Brazil); Carina Regina de Macedo (LEGOS, Université de Toulouse, CNRS, OMP, IRD ; Univ. Littoral Côte d'Opale, CNRS, Univ. Lille, IRD, UMR 8187 – LOG – Laboratoire d'Océanologie et de Géosciences ; Earth Observation and Geoinformatics Division, National Institute for Space Research (INPE), France / Brazil ); Michel Tchilibou (Collecte Localisation Satellites (CLS), France); Camila Artana (Laboratoire LOCEAN-IPSL, Sorbonne Universités, UPMC, Univ. Paris 6-CNRS-IRD-MNHN, France); Isabelle Dadou (LEGOS, Université de Toulouse, CNRS, OMP, IRD, France); Antoine Delepoulle (Collecte Localisation Satellites (CLS), France); Maxime Ballarota (Collecte Localisation Satellites (CLS) , France); Loren Carrère (Collecte Localisation Satellites (CLS), France); Simon Barbot (LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, France); Alex Costa (Departamento de Oceanografia, Universidade Federal de Pernambuco (DOCEAN/UFPE) , Brazil); M'hamdi Amine (LEGOS, Université de Toulouse, CNRS, OMP, IRD ; Departamento de Oceanografia, Universidade Federal de Pernambuco (DOCEAN/UFPE) ; CECI CNRS/Cerfacs/IRD, Université de Toulouse , France - Brazil)

Off the Amazon shelf, mesoscale eddies interact with internal solitary waves (ISWs), altering their characteristics. For the first time, these interactions are observable through repeated, direct measurements by the Surface Water and Ocean Topography (SWOT) mission, combined with MODIS and NOAA-20 sunglint imagery. This study aims to analyze ISWs observable from SWOT’s Absolute Dynamic Topography (ADT) and to characterize the changes in their properties when interacting with eddies. The analysis focuses on three cases: ISW propagation in the absence of eddies, ISW refraction refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. Using a spectral analysis method combined with band-pass filtering, ISWs crests were detected and extracted. This approach enabled the accurate tracking of ISW features, such as propagation direction, distances between individual ISWs crest, and wavefront geometry. Prior to ISW-eddy interaction, mode-1 ISWs propagated without changes in propagation direction and with plane wavefronts. A key finding was that different ISW responses were observed after interaction with eddies. In the first case, without the eddy, the passage of ISWs over a seamount led to energy transfer from mode-1 ISWS to mode-3 ISWs, although the propagation direction remained unchanged. In the second case, with a cyclonic eddy over the seamount, ISW trajectories were deflected westward by approximately 50°. In addition, the wavefront curvature was increased, and shifts to mode-3 ISWs were observed. In the third case, at the western edge of an anticyclonic eddy near the seamount, ISWs were diffracted into two distinct direction. One part was refracted westward (~42°), exhibiting wavefront flattening and a reduction in the distances between crests. The second propagated eastward (~15°) along the anticyclone’s edge, with surface manifestation of wave packet structures and increased wavefront curvature. These results demonstrate that the proposed method effectively captures the complex dynamics of ISWs. The results provide new insights into the nonlinear behavior of ISWs and their interactions with (sub)mesoscale oceanographic features.