Breaking of Internal Waves and Turbulent Dissipation in an Anticyclonic Mode Water Eddy

Type Article
Date 2020-07
Language English
Author(s) Fernández-Castro Bieito1, Evans Dafydd Gwyn2, Frajka-Williams Eleanor2, Vic Clement3, Naveira-Garabato Alberto C.4
Affiliation(s) 1 : Departamento de Oceanografía, Instituto de Investigacións Mariñas (IIM-CSIC), Vigo, Spain
2 : National Oceanography Centre, Southampton, UK
3 : Laboratoire d’Océanographie Physique et Spatiale, UBO-CNRS-IFREMER-IRD, IUEM, Plouzané, France
4 : Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, UK
Source Journal Of Physical Oceanography (0022-3670) (American Meteorological Society), 2020-07 , Vol. 50 , N. 7 , P. 1893-1914
DOI 10.1175/JPO-D-19-0168.1
WOS© Times Cited 2
Abstract

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.

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Fernández-Castro Bieito, Evans Dafydd Gwyn, Frajka-Williams Eleanor, Vic Clement, Naveira-Garabato Alberto C. (2020). Breaking of Internal Waves and Turbulent Dissipation in an Anticyclonic Mode Water Eddy. Journal Of Physical Oceanography, 50(7), 1893-1914. Publisher's official version : https://doi.org/10.1175/JPO-D-19-0168.1 , Open Access version : https://archimer.ifremer.fr/doc/00615/72734/