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Abstract. Wind work at the air-sea interface is the transfer of kinetic energy between the ocean and the atmosphere and, as such, is an important part of the ocean-atmosphere coupled system. Wind work is defined as the scalar product of ocean wind stress and surface current, with each of these two variables spanning, in this study, a broad range of spatial and temporal scales, from 10 km to more than 3000 km and hours to months. These characteristics emphasize wind work's multiscale nature. In the absence of appropriate global observations, our study makes use of a new global, coupled ocean-atmosphere simulation, with horizontal grid spacing of 2–5 km for the ocean and 7 km for the atmosphere, analyzed for 12 months.We develop a methodology, both in physical and spectral spaces, to diagnose three different components of wind work that force distinct classes of ocean motions, including high-frequency internal gravity waves, such as near-inertial oscillations, low-frequency currents such as those associated with eddies, and seasonally averaged currents, such as zonal tropical and equatorial jets.The total wind work, integrated globally, has a magnitude close to 5 TW, a value that matches recent estimates. Each of the first two components that force high-frequency and low-frequency currents, accounts for ∼ 28 % of the total wind work and the third one that forces seasonally averaged currents, ∼ 44 %. These three components, when integrated globally, weakly vary with seasons but their spatial distribution over the oceans has strong seasonal and latitudinal variations. In addition, the high-frequency component that forces internal gravity waves, is highly sensitive to the collocation in space and time (at scales of a few hours) of wind stresses and ocean currents. Furthermore, the low-frequency wind work component acts to dampen currents with a size smaller than 250 km and strengthen currents with larger sizes. This emphasizes the need to perform a full kinetic budget involving the wind work and nonlinear advection terms as small and larger-scale low-frequency currents interact through these nonlinear terms.The complex interplay of surface wind stresses and currents revealed by the numerical simulation motivates the need for winds and currents satellite missions to directly observe wind work.
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Coastally Generated Near-Inertial Waves
Wind directly forces inertial oscillations in the mixed layer. Where these currents hit the coast, the no-normal-flow boundary condition leads to vertical velocities that pump both the base of the mixed layer and the free surface, producing offshore-propagating near-inertial internal and surface waves, respectively. The internal waves directly transport wind work downward into the ocean’s stratified interior, where it may provide mechanical mixing. The surface waves propagate offshore where they can scatter over rough topography in a process analogous to internal-tide generation. Here, we estimate mixed layer currents from observed winds using a damped slab model. Then, we estimate the pressure, velocity, and energy flux associated with coastally generated near-inertial waves at a vertical coastline. These results are extended to coasts with arbitrary across-shore topography and examined using numerical simulations. At the New Jersey shelfbreak, comparisons between the slab model, numerical simulations, and moored observations are ambiguous. Extrapolation of the theoretical results suggests that [Formula: see text](10%) of global wind work (i.e., 0.03 of 0.31 TW) is transferred to coastally generated barotropic near-inertial waves.
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- Award ID(s):
- 1635560
- PAR ID:
- 10124264
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Physical Oceanography
- Volume:
- 49
- Issue:
- 11
- ISSN:
- 0022-3670
- Page Range / eLocation ID:
- p. 2979-2995
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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