Near-Inertial Energy Propagation from the Mixed Layer: Theoretical Considerations

Zervakis, Vassilis; Levine, Murray D.

doi:10.1175/1520-0485(1995)025<2872:niepft>2.0.co;2

Cited by 44 publications

(47 citation statements)

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“…Subsequent propagation into the thermocline can be described in terms of normal modes (Gill 1984), or rays (Kroll 1975;Zervakis and Levine 1995;Garrett 2001). Single-depth measurements such as those presented here cannot distinguish vertical structure of individual waves.…”

Section: Introductionmentioning

confidence: 89%

Seasonal and Spatial Variability of Near-Inertial Kinetic Energy from Historical Moored Velocity Records

Alford

Whitmont

2007

Journal of Physical Oceanography

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Temporal and spatial patterns of near-inertial kinetic energy (KE moor ) are investigated in a database of 2480 globally distributed, moored current-meter records (deployed on 690 separate moorings) and compared with the distribution of wind-forced mixed-layer energy flux F ML . By computing KE moor using short (30 day) multitaper spectral windows, the seasonal cycle is resolved. Clear winter enhancement by a factor of 4-5 is seen in the Northern Hemisphere for latitudes 25°-45°at all depths Ͻ4500 m, in close agreement with the magnitude, phase, and latitudinal dependence of the seasonal cycle of F ML . In the Southern Hemisphere, data coverage is poorer, but a weaker seasonal cycle (a factor of 2) in both KE moor and F ML is still resolvable between 35°and 50°. When Wentzel-Kramers-Brillouin (WKB) scaled using climatological buoyancy-frequency profiles, summer KE moor is approximately constant in depth while showing a clear decrease by a factor of 4-5 from 500 to 3500 m in winter. Spatial coverage is sufficient in the Northern Hemisphere to resolve broad KE moor maxima in the western portion of each ocean basin in winter, generally collocated with F ML maxima associated with storm forcing. The ratio of depth-integrated KE moor to F ML gives a replenishment time scale, which is about 10 days in midlatitudes, consistent with 1) previous estimates of the dissipation time scale of the internal wave continuum and 2) the presence of a seasonal cycle. Its increase to Ϸ70-80 days at lower latitudes is a possible signature of equatorward propagation of near-inertial waves. The seasonal modulation of the magnitude of KE moor , its similarity to that in F ML , and the depth decay and western intensification in winter but not in summer are consistent with a primarily wind-forced near-inertial field for latitudes poleward of Ϸ25°.

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Section: Introductionmentioning

confidence: 89%

Seasonal and Spatial Variability of Near-Inertial Kinetic Energy from Historical Moored Velocity Records

Alford

Whitmont

2007

Journal of Physical Oceanography

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“…At the ocean surface, time-variable wind stresses force inertial motions in the surface mixed layer, since the inertial frequency is the natural "ringing" frequency of any fluid on a rotating planet (Section 3.2). Simple models predict that most of the energy goes into low-mode internal waves (Gill, 1984;Zervakis and Levine, 1995). The horizontal wavelength of the propagating waves is heavily influenced by the beta effect, namely that for a patch large enough to feel the latitudinal change of inertial frequency, motions at the northern end of the patch gradually get out of phase with those near the southern end.…”

Section: Dissipation Near-inertial Wave Generation Sitesmentioning

confidence: 99%

Diapycnal Mixing Processes in the Ocean Interior

MacKinnon

Laurent

Garabato

2013

International Geophysics

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“…In a separate study, Zervakis and Levine (1995) used an unforced, linear, three-dimensional, numerical model on a b plane to track the evolution of an initial excitation of inertial oscillations in a slab mixed layer. The solution was expanded in vertical modes and solved numerically, allowing for horizontal propagation.…”

Section: Internal Wave Activitymentioning

confidence: 99%

“…The Ocean Storms Experiment (see Oceans Storms collection of papers: D 'Asaro 1995a,b,c;Niiler and Paduan 1995;Large and Crawford 1995;Qi et al 1995;Zervakis and Levine 1995;Levine and Zervakis 1995;Large et al 1995) was an effort to examine more closely the processes of air-sea interaction using a collection of moored and drifting instruments, and our interest here is the response of the mixed layer to surface forcing and the mechanisms responsible for the momentum transfer below the mixed layer. We approach this through analysis of previously unreported moored observations taken during Ocean Storms for two distinct autumn storms with clear but dramatically different upper-ocean responses.…”

Section: Introductionmentioning

confidence: 99%

Mixing in the Transition Layer during Two Storm Events

Dohan

Davis

2011

Journal of Physical Oceanography

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Upper-ocean dynamics analyzed from mooring-array observations are contrasted between two storms of comparable magnitude. Particular emphasis is put on the role of the transition layer, the strongly stratified layer between the well-mixed upper layer, and the deeper more weakly stratified region. The midlatitude autumn storms occurred within 20 days of each other and were measured at five moorings. In the first storm, the mixed layer follows a classical slab-layer response, with a steady deepening during the course of the storm and little mixing of the thermocline beneath. In the second storm, rather than deepening, the mixed layer shoals while intense near-inertial waves are resonantly excited within the mixed layer. These create a large shear throughout the transition layer, generating turbulence that broadens the transition layer.Details of the space-time structure of the frequencies in both short waves and near-inertial waves are presented. Small-scale waves are excited within the transition layer. Their frequencies change with time and there are no clear peaks at harmonics of inertial or tidal frequencies. Wavelet transforms of the inertial oscillations show the evolution as a spreading in frequency, a deepening of the core into the transition layer, and a shift off the inertial frequency. A second near-inertial energy core appears below the transition layer at all moorings coincident with a rapid decay of mixed layer currents.An overall result is that direct wind-generated motions extend to the depth of the transition layer. The transition layer is a location of enhanced wave activity and enhanced shear-driven mixing.

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Near-Inertial Energy Propagation from the Mixed Layer: Theoretical Considerations

Cited by 44 publications

References 0 publications

Seasonal and Spatial Variability of Near-Inertial Kinetic Energy from Historical Moored Velocity Records

Seasonal and Spatial Variability of Near-Inertial Kinetic Energy from Historical Moored Velocity Records

Diapycnal Mixing Processes in the Ocean Interior

Mixing in the Transition Layer during Two Storm Events

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