A conjecture relating oceanic internal waves and small‐scale processes

Holloway, Greg

doi:10.1080/07055900.1983.9649159

Cited by 56 publications

(39 citation statements)

References 42 publications

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“…As will be discussed below, these high-frequency internal waves themselves are the result of nonlinear interaction between inertial motions and tidal currents, which not only has its influence on the mixing across stratification, but also on the particular form of the internal wave spectrum, with its canonical [Garett and Munk, [Mihaly et al, 1998] on the importance of nearinertial motions in internal wave band energy transfer, which also confirmed earlier suggestions [Holloway, 1980[Holloway, , 1983 that internal wave interaction is likely strong. This is reflected in a near-constant Ri --1, as observed [ Figure l(c)], and it may explain the consistency of the internal wave spectrum [Munk, 1981] interaction frequencies to a uniform o'2-decay in frequency and, when scaled with the local buoyancy frequency, to a fixed level to within a factor of two, as in deep ocean data [Fofonoff and Webster, 1971].…”

Section: Observationssupporting

confidence: 68%

Strong inertial currents and marginal internal wave stability in the central North Sea

Haren¹,

Maas²,

Zimmerman³

et al. 1999

Geophysical Research Letters

116

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Abstract.Solar insolation stabilizes the water column and suppresses vertical exchange. Observations from the central North Sea clearly show that increased heating in summer is accompanied by enhanced de-stabilizing vertical current differences (shear), surprisingly to such extent that the equilibrium state is marginally stable. Under calm weather conditions, the shear is predominantly generated by nearinertial motions while the internal wave spectrum primarily results from nonlinear interaction between the dominating tidal and near-inertial motions. In terms of the associated enhanced vertical mixing across the largest vertical temperature gradients, shelf seas are not different from the abyssal ocean, despite the proximity to energy sources near boundaries in the former. By the lack of sufficiently strong wind-and tidal mixing this internal mixing is considered to be responsible for the diapycnal transport of nutrients leading to the observed increase in near-surface values and triggering the late-summer phytoplankton bloom.

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Section: Observationssupporting

confidence: 68%

Strong inertial currents and marginal internal wave stability in the central North Sea

Haren¹,

Maas²,

Zimmerman³

et al. 1999

Geophysical Research Letters

116

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“…A semidiurnal tidal strain peak is also seen, centered at zero wavenumber, associated with scales large compared to the 420-m vertical measurement window. At scales smaller than 20 m, the wave and vortical signals merge owing to Doppler smearing, as suggested by Holloway (1983). In terms of wavenumberfrequency spectral density, the vortical peak appears to dominate.…”

Section: Observations Of Strain: 1983-2002mentioning

confidence: 80%

“…Following a fluid parcel, potential vorticity is constant in the absence of nonadiabatic processes (Ertel 1942). Furthermore, propagating internal gravity waves do not induce fluctuations in potential vorticity (Holloway 1983;Muller 1984), whereas finite potential vorticity anomalies are anticipated for quasigeostrophic flows.…”

Section: Introductionmentioning

confidence: 92%

“…Still, Holloway (1983) cautioned that there are motions at fine vertical scales in the sea that are not internal waves. He suggested that small-scale quasigeostrophic motions are Doppler shifted by the ambient currents across the internal wave frequency band and contribute significantly to observed finescale shear and strain estimates.…”

Section: A Brief Historical Reviewmentioning

confidence: 99%

“…1). This has proven challenging, experimentally, because lateral and vertical Doppler shifting cause extensive overlap in temporal scales (e.g., Holloway 1983), ostensibly frustrating any attempt to separate the data using a simple frequency filter.…”

Section: Introductionmentioning

confidence: 99%

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Vortical and Internal Wave Shear and Strain

Pinkel

2014

Journal of Physical Oceanography

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Depth-time records of isopycnal vertical strain have been collected from intensive CTD profiling programs on the research platform (R/P) Floating Instrument Platform (FLIP). The associated vertical wavenumber frequency spectrum of strain, when viewed in an isopycnal-following frame, displays a clear spectral gap at low vertical wavenumber, separating the quasigeostrophic (vortical) strain field and the superinertial internal wave continuum. This gap enables both model and linear-filter-based methods for separating the submesoscale and internal wave strain fields. These fields are examined independently in six field programs spanning the period 1983-2002. Vortical and internal wave strain variances are often comparable in the upper thermocline, of order 0.2. However, vortical strain tends to decrease with increasing depth (decreasing buoyancy frequency , exceeding vortical variance by a factor of 5-10 at depths below 500 m.In contrast to strain, the low-frequency spectral gap in the shear spectrum is largely obscured by Dopplersmeared near-inertial motions. The vertical wavenumber spectrum of anticyclonic shear exceeds the cyclonic shear and strain spectra at all scales greater than 10 m. The frequency spectrum of anticyclonic shear exceeds that of both cyclonic shear and strain to frequencies of 0.5 cph, emphasizing the importance of lateral Doppler shifting of near-inertial shear.The limited Doppler shifting of the vortical strain field implies surprisingly small submesoscale aspect ratios: k H /k z ; 0.001, Burger numbers Br 5 k H N/k z f ; 0.1. Submesoscale potential vorticity is dominated by vertical straining rather than the vertical component of relative vorticity. The inferred rms fluctuation of fluid vorticity is far less for the vortical field than for the internal wavefield.

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6.3.6 Spectral models

Olbers¹

Landolt-Börnstein - Group v Geophysics

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A conjecture relating oceanic internal waves and small‐scale processes

Cited by 56 publications

References 42 publications

Strong inertial currents and marginal internal wave stability in the central North Sea

Strong inertial currents and marginal internal wave stability in the central North Sea

Vortical and Internal Wave Shear and Strain

6.3.6 Spectral models

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