Stratified tidal flow over a tall ridge above and below the turning latitude

Musgrave, Ruth; Pinkel, R.; MacKinnon, Jennifer A.; Mazloff, Matthew R.; Young, W. R.

doi:10.1017/jfm.2016.150

Cited by 18 publications

(19 citation statements)

References 42 publications

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“…The model neglects interactions among lee waves as well as with the background internal-wave field, tides, bottom-trapped topographic waves (Rhines 1970), the subinertial (jkUj , jfj) and superbuoyancy (jkUj . N) forced evanescent response (Musgrave et al 2016;Klymak 2018) including blocking and splitting (Nikurashin et al 2014), bottom Ekman shear and shed vortices (D'Asaro 1988). A particular concern is the linearized boundary condition (7) which assumes that blocking at lower topographic wavenumbers does not impact lee-wave generation at higher wavenumbers (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…In the ocean, topographic variability is not confined to a single wavenumber but distributed over a range of lengthscales that can be described by a horizontal wavenumber spectrum for topographic height S [h](k). The flow/topography response radiates upward into the water column as lee waves for jf/Uj , jkj , jN/Uj but is evanescent (bottom-trapped) outside this topographic wavenumber band (Musgrave et al 2016). Internal lee-wave properties are determined by flow speed U, buoyancy frequency N, Coriolis frequency f, the topographic height field h(x, y) or its spectral distribution S[h](k, '), and topographic wavevector (k, '), where ' is the cross-stream wavenumber.…”

Section: Lee-wave Generationmentioning

confidence: 99%

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Energy Sinks for Lee Waves in Shear Flow

Kunze

Lien

2019

Journal of Physical Oceanography

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Microstructure measurements in Drake Passage and on the flanks of Kerguelen Plateau find turbulent dissipation rates ε on average factors of 2–3 smaller than linear lee-wave generation predictions, as well as a factor of 3 smaller than the predictions of a well-established parameterization based on finescale shear and strain. Here, the possibility that these discrepancies are a result of conservation of wave action E/ ω L = E/| kU| is explored. Conservation of wave action will transfer a fraction of the lee-wave radiation back to the mean flow if the waves encounter weakening currents U, where the intrinsic or Lagrangian frequency ω L = | kU| ↓ | f| and k the along-stream horizontal wavenumber, where kU ≡ k ⋅ V. The dissipative fraction of power that is lost to turbulence depends on the Doppler shift of the intrinsic frequency between generation and breaking, hence on the topographic height spectrum and bandwidth N/ f. The partition between dissipation and loss to the mean flow is quantified for typical topographic height spectral shapes and N/ f ratios found in the abyssal ocean under the assumption that blocking is local in wavenumber. Although some fraction of lee-wave generation is always dissipated in a rotating fluid, lee waves are not as large a sink for balanced energy or as large a source for turbulence as previously suggested. The dissipative fraction is 0.44–0.56 for topographic spectral slopes and buoyancy frequencies typical of the deep Southern Ocean, insensitive to flow speed U and topographic splitting. Lee waves are also an important mechanism for redistributing balanced energy within their generating bottom current.

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Section: Discussionmentioning

confidence: 99%

Section: Lee-wave Generationmentioning

confidence: 99%

Energy Sinks for Lee Waves in Shear Flow

Kunze

Lien

2019

Journal of Physical Oceanography

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“…Similarly, near-field tidal dissipation can be increased by topographically trapped internal waves generated by subinertial tidal constituents (Tanaka et al 2013), that is, the diurnal constituents at latitudes >30° and the semidiurnal constituents at latitudes >74.5°. The energy density in such trapped motions increases with latitude and is all dissipated locally (Musgrave et al 2016).…”

Section: N E Ar -Fie Ld Tidal M Ixingmentioning

confidence: 99%

Climate Process Team on Internal Wave–Driven Ocean Mixing

MacKinnon

Zhao

Whalen

et al. 2017

Bulletin of the American Meteorological Society

272

207

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O cean turbulence influences the transport of heat, freshwater, dissolved gases such as CO 2 , pollutants, and other tracers. It is central to understanding ocean energetics and reducing uncertainties in global circulation and simulations from climate models. The dissipation of turbulent energy in stratified water results in irreversible diapycnal (across density surfaces) mixing. Recent work has shown that the spatial and temporal inhomogeneity in diapycnal mixing may play a critical role in a variety of climate phenomena. Hence, a quantitative understanding of the physics that drive the distribution of diapycnal mixing in the ocean interior is fundamental to understanding the ocean's role in climate.Diapycnal mixing is very difficult to accurately parameterize in numerical ocean models for two reasons. The first one is due to the discrete representation of tracer advection in directions that are not perfectly aligned with isopycnals, which can result in numerically induced mixing from truncation errors that is larger than observed diapycnal mixing (Griffies et al. 2000;Ilıcak et al. 2012). The second reason is related to the intermittency of turbulence, which is generated by complex and chaotic motions that span a large space-time range. Furthermore, this mixing is driven by a wide range of processes with distinct governing physics that create a rich global geography [see MacKinnon et al. (2013c) for a review]. The difficulty is also related to the relatively sparse direct sampling of ocean mixing, whereby sophisticated ship-based measurements are generally required to accurately characterize ocean mixing processes. Nonetheless, we have sufficient evidence from theory, process models, laboratory experiments, and field measurements to conclude that away from ocean boundaries (atmosphere, ice, or the solid ocean bottom), diapycnal mixing is largely related to the breaking of internal gravity waves, which have a complex dynamical underpinning and associated geography. The study summarizes recent advances in our understanding of internal wave-driven turbulent mixing in the ocean interior and introduces new parameterizations for global climate ocean models and their climate impacts.

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“…Tidal flow over topography in a region a long distance poleward of the critical latitude generates laterally trapped waves with a decay scale that decreases with latitude (Musgrave, Pinkel, et al, ). Closer to the critical latitude, standard linear theories produce solutions that are sensitive to latitude.…”

Section: Internal Hydraulic Flowmentioning

confidence: 99%

Tidally Modulated Internal Hydraulic Flow and Energetics in the Central Canadian Arctic Archipelago

et al. 2018

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The Canadian Arctic Archipelago is a key conduit for comparatively fresh Arctic waters flowing to the Atlantic. Model estimates of the freshwater outflow, which is strongly correlated with the volume flux, contain major uncertainties because most existing models exclude tides, marginally resolve the internal Rossby radius, or both. At the same time, barotropic tidal models preclude stratified flow effects. Here we assess the relative importance of barotropic and baroclinic processes to water mass transformation, friction, and energy losses motivated by processes observed in a fine‐scale survey in the central Archipelago. A sharp separation of warmed Canada Basin water and locally formed water is observed over a long sill in a narrow channel and coincides with an internal hydraulic jump caused by the mean flow. Tidal currents, however, modulate the jump, as demonstrated by both scale analysis and a two‐dimensional simulation. The jump, together with internal tides propagating as Kelvin waves, leads to isopycnal displacements up to 50 m. The generation of these internal Kelvin waves has a leading‐order role in a regional energy budget. It is small, however, relative to bottom boundary layer dissipation, which accounts for an estimated 50% of the total tidal energy losses. Consequently, adding tides needs to be a priority for regional models.

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Stratified tidal flow over a tall ridge above and below the turning latitude

Cited by 18 publications

References 42 publications

Energy Sinks for Lee Waves in Shear Flow

Energy Sinks for Lee Waves in Shear Flow

Climate Process Team on Internal Wave–Driven Ocean Mixing

Tidally Modulated Internal Hydraulic Flow and Energetics in the Central Canadian Arctic Archipelago

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