Breaking of internal waves and turbulent dissipation in an anticyclonic mode Water Eddy

• Published in: Journal of Physical Oceanography
• Main Authors: Fernández-Castro, Bieito, Evans, Gwyn, Frajka-Williams, Eleanor, Vic, Clément, Naveira-Garabato, Alberto C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: North Atlantic
• Online Access: http://nora.nerc.ac.uk/id/eprint/527721/; https://nora.nerc.ac.uk/id/eprint/527721/1/jpo-d-19-0168.1.pdf; https://nora.nerc.ac.uk/id/eprint/527721/7/jpod190168.pdf; https://doi.org/10.1175/JPO-D-19-0168.1

A four-month glider mission was analyzed to assess turbulent dissipation in an anticyclonic eddy at the western boundary of the subtropical North Atlantic. The eddy (radius ≈ 60 km) had a core of low potential vorticity between 100–450 m, with maximum radial velocities of 0.5 m s−1 and Rossby number ≈ −0.1. Turbulent dissipation was inferred from vertical water velocities derived from the glider flight model. Dissipation was suppressed in the eddy core (ε ≈ 5×10−10 W kg−1) and enhanced below it (> 10−9 W kg−1). Elevated dissipation was coincident with quasi-periodic structures in the vertical velocity and pressure perturbations, suggesting internal waves as the drivers of dissipation. A heuristic ray-tracing approximation was used to investigate the wave-eddy interactions leading to turbulent dissipation. Ray-tracing simulations were consistent with two types of wave-eddy interactions that may induce dissipation: the trapping of near-inertial wave energy by the eddy’s relative vorticity, or the entry of an internal tide (generated at the nearby continental slope) to a critical layer in the eddy shear. The latter scenario suggests that the intense mesoscale field characterizing the western boundaries of ocean basins might act as a ‘leaky wall’ controlling the propagation of internal tides into the basins’ interior.