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, Dafydd Gwyn, Frajka-Williams, Eleanor, Vic, Clément, Naveira-garabato, Alberto C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: North Atlantic
• Online Access: https://eprints.soton.ac.uk/441026/; https://eprints.soton.ac.uk/441026/1/jpo_d_19_0168.1.pdf; https://eprints.soton.ac.uk/441026/2/jpod190168.pdf

A 4-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 and 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 Wkg -1 ) and enhanced below it (>10 -9 Wkg -1 ). Elevated dissipation was coincident with quasiperiodic 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 basin’s interior.