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

2020; American Meteorological Society; Volume: 50; Issue: 7 Linguagem: Inglês

10.1175/jpo-d-19-0168.1

1520-0485

Bieito Fernández Castro, Dafydd Gwyn Evans, Eleanor Frajka‐Williams, Clément Vic, Alberto C. Naveira Garabato,

Climate variability and models

Abstract 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 W kg −1 ) and enhanced below it (>10 −9 W kg −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.