Internal solitary waves refraction and diffraction from interaction with eddies off the Amazon Shelf from SWOT

Abstract. Off the Amazon shelf, mesoscale eddies interact with internal solitary waves (ISWs), modifying their characteristics. For the first time, such interactions are directly observed through repeated measurements from a set of high-resolution satellite data, including the recently launched SWOT (Surface Water and Ocean Topography) mission. This study investigates ISWs detectable in SWOT Absolute Dynamic Topography (ADT) and characterizes the changes in their properties induced by interactions with mesoscale eddies.

The analysis focuses on three scenarios: ISW propagation in the absence of eddies, ISW refraction by a cyclonic eddy, and ISW diffraction by an anticyclonic eddy. ISW crests were identified and extracted using a band-pass filtering technique, allowing accurate tracking of key features such as propagation direction, spacing between individual crests, and wavecrest geometry. Before any interaction with eddies, mode-1 ISWs propagate steadily, with consistent direction and planar wavefronts. A key finding is the variety of ISW responses depending on eddy conditions. In the first case, in the absence of eddy, the interaction of ISWs with a seamount induced energy transfer from mode-1 to mode-3 ISWs, while the propagation direction remains unchanged. In the second case, a cyclonic eddy overlaying the seamount refracted ISW trajectories westward by approximately 50°, while also increasing wavecrest curvature and enhancing the generation of mode-3 waves. In the third case, at the western edge of an anticyclonic eddy near the seamount, the ISWs are split into two distinct paths: one branch refracted westward, exhibiting flatter wave crests and reduced spacing between them; the other branch followed the eastern edge of the eddy, displaying surface signatures of wave packets and enhanced wavecrest curvature.

These results demonstrate the effectiveness of the proposed approach in capturing the complex dynamics of ISWs. They offer novel insights into the nonlinear behavior of ISWs and their interactions with mesoscale and submesoscale oceanic features.