Jody Klymak (University of Victoria, Canada); Tetjana Ross (Institute of Ocean Sciences, Fisheries and Oceans Canada (DFO), Canada); Guoqi Han (Institute of Ocean Sciences, Fisheries and Oceans Canada (DFO), Canada)

The california undercurrent in the Northeast Pacific interacts with the shelf break creating instabilities associated with the generation of sub surface eddies called Cuddies. These subthermocline eddies are key agents in offshore transport of heat, salt, oxygen and nutrients, yet their limited surface expression has historically hindered their detection via traditional satellite altimetry. In this study, we investigate the vertical and horizontal structure of a Cuddy, using underwater glider observations and satellite data, including the high-resolution Surface Water and Ocean Topography (SWOT) mission. Glider transects reveal a subsurface-intensified lens at ~250 m depth, characterized by warm and salty Pacific Equatorial Waters. SWOT captures the eddy with greater intensity and finer-scale structure than conventional altimetry (DUACS), resolving submesoscale features and spiral-shaped internal jets not seen in DUACS. In addition, SWOT-derived geostrophic velocities were compared with surface velocities inferred from satellite chlorophyll imagery showing high correlation (R2 = 0.78). These results highlight SWOT’s unique capability to detect the submesoscale surface imprint of subsurface eddies, enhancing our understanding of eastern boundary current dynamics and cross-shelf exchange