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Byron F. Kilbourne and James B. Girton

caveats about gridded wind products, the wind work may still be an overestimate in spite of the fact that surface current amplitudes are well predicted by the slab model. Additionally, the downward flux estimate relies on the assumption of constant vertical group velocity and can only be regarded as a ballpark figure. Nevertheless, the agreement suggests that most of the near-inertial wind energy input is able to radiate from the mixed layer as propagating near-inertial internal waves. Acknowledgments

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Jesse M. Cusack, Alberto C. Naveira Garabato, David A. Smeed, and James B. Girton

.4 N m −2 . In comparison, mean flow velocity vectors are orientated eastward ( Fig. 6a ) in the opposite direction to the mean momentum flux. The limitations of the floats’ spatiotemporal sampling of the wave mean that we cannot definitively establish whether the wave is imparting a drag on the mean flow or radiating horizontal momentum elsewhere . Fig . 9. Vertical flux of horizontal momentum vectors , labeled by profile number. Arrow color denotes the vertical energy flux. Depth is contoured in

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J. Alexander Brearley, Katy L. Sheen, Alberto C. Naveira Garabato, David A. Smeed, and Stephanie Waterman

U 0 is the low-pass-filtered current velocity, k = ( k , l ) is the horizontal wavenumber vector along and across the mean flow, and P ( k ) is the 2D topography spectrum. To account for saturation of the energy flux that occurs at supercritical topography, the steepness parameter L = N √2 h / U 0 is calculated, where h is the topographic height in the radiative wavenumber range. When this value exceeds 0.7, E rad is multiplied by (0.7/ L ) 2 . Fig . 13. (a) 2D topography power

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Michael Bates, Ross Tulloch, John Marshall, and Raffaele Ferrari

) . Here, we focus on an eddy diffusivity that can be used for tracers—including potential vorticity—that depends on the state of the large-scale flow and so can change as the climate changes. Recently, Abernathey and Marshall (2013) estimated the surface cross-stream eddy diffusivity for passive tracers by diagnosing the part of the downgradient eddy flux associated with irreversible mixing using the Osborn and Cox (1972) relation, as described in section 2 . They show overall agreement with the

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Alberto C. Naveira Garabato, Kurt L. Polzin, Raffaele Ferrari, Jan D. Zika, and Alexander Forryan

“Reynolds decomposition” of variables into a slowly changing mean state (indicated by an overbar) and fluctuations (denoted by primes) has been adopted to allow investigation of the influence of the fluctuations on the mean. Here, u is the three-dimensional velocity vector, and κ is the molecular diffusivity of θ . The first term on the right-hand side represents the eddy flux. The second term is the dissipation of mean potential temperature gradients by molecular motions and may be generally

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Sophia T. Merrifield, Louis St. Laurent, Breck Owens, Andreas M. Thurnherr, and John M. Toole

associated with density fronts flow over rough topography, generating internal lee waves that radiate energy and provide power for turbulence in the stratified ocean interior (e.g., Nikurashin and Ferrari 2010 ). Water mass variability and strong mesoscale activity also precondition the water column for double-diffusive instability (e.g., Joyce et al. 1978 ). Because of the remoteness and harsh conditions, few direct measurements of mixing have been made in the Southern Ocean. A growing body of work

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