Spatial and temporal distribution of the wind‐induced internal wave energy available for deep water mixing in the North Pacific

Nagasawa, Mitsuru; Niwa, Yuki; Hibiya, Taketoshi

doi:10.1029/2000jc900019

Cited by 79 publications

(50 citation statements)

References 42 publications

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“…after propagation to lower latitudes, (e.g. Nagasawa et al 2000)). For the instability to develop, both inertial and thermal wind shear must be present, since the latter can lower the minimum frequency of inertia-gravity waves (1.1) to a subharmonic of the inertial frequency.…”

Section: Discussionmentioning

confidence: 99%

“…In principle, using classical inertia-gravity wave theory, parametric subharmonic instability can be ruled out as a local damping mechanism for inertial motions because the classical dispersion relation does not allow for freely-propagating waves of frequency f /2. Non-locally though, near-inertial waves that propagate equatorward, and hence become superinertial, can undergo parametric subharmonic instability when they reach the latitude where the local inertial frequency is half their frequency (Nagasawa, Niwa & Hibiya 2000).…”

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confidence: 99%

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Damping of inertial motions by parametric subharmonic instability in baroclinic currents

Thomas

Taylor

2014

J. Fluid Mech.

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A new damping mechanism for vertically-sheared inertial motions is described involving an inertia-gravity wave that oscillates at half the inertial frequency, f , and that grows at the expense of inertial shear. This parametric subharmonic instability forms in baroclinic, geostrophic currents where thermal wind shear, by reducing the potential vorticity of the fluid, allows inertia-gravity waves with frequencies less than f . A stability analysis and numerical simulations are used to study the instability criterion, energetics, and finite-amplitude behaviour of the instability. For a flow with uniform shear and stratification, parametric subharmonic instability develops when the Richardson number of the geostrophic current nears Ri PSI = 4/3 + γ cos φ, where γ is the ratio of the inertial to thermal wind shear magnitude and φ is the angle between the inertial and thermal wind shears at the initial time. Inertial shear enters the instability criterion because it can also modify the potential vorticity and hence the minimum frequency of inertia-gravity waves. When this criterion is met, inertia-gravity waves with a frequency f /2 and with flow parallel to isopycnals amplify, extracting kinetic energy from the inertial shear through shear production. The solutions of the numerical simulations are consistent with these predictions and additionally show that finite-amplitude parametric subharmonic instability both damps inertial shear and is itself damped by secondary shear instabilities. In this way, parametric subharmonic instability opens a pathway to turbulence where kinetic energy in inertial shear is transferred to small scales and dissipated.

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Damping of inertial motions by parametric subharmonic instability in baroclinic currents

Thomas

Taylor

2014

J. Fluid Mech.

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“…This energy is presumably associated with near-inertial internal waves (NIWs) that are generated north of the island chain by intermittent storms (Nagasawa et al 2000). While tides beat regularly in time, the energy input from the wind to the NIW field is highly intermittent, and occurs primarily during winter storms in mid-to high latitudes (Alford 2003).…”

Section: Introductionmentioning

confidence: 99%

Boundary Mixing Associated with Tidal and Near-Inertial Internal Waves

Aucan

Merrifield

2008

Journal of Physical Oceanography

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Moorings deployed on the south (August-November 2002) and north (November 2002-June 2003 flanks of the Kaena Ridge, Hawaii, are used to document the flow variability associated with mixing within 200 m from the boundary, deep along the ridge, as part of the Hawaii Ocean Mixing Experiment (HOME). At both sites, strong temperature inversions are detected with vertical scales of ϳ100 m. A Thorpe-scale analysis of the overturns yields a time-averaged dissipation near the bottom at the south site (1.2 ϫ 10 Ϫ8 W kg Ϫ1 ) that is 10 times higher than the north site (1.9 ϫ 10 Ϫ9 W kg Ϫ1 ), with both higher than the dissipation at similar depths 30 km from the ridge. On the south flank, observed horizontal currents and vertical displacements are dominated by the semidiurnal internal tide. On the north flank, the semidiurnal tide is less energetic than on the south, with a different vertical structure as tidal amplitudes decrease toward the boundary. These differences are attributed to greater separation from the bottom of downward-propagating internal tides at the north site compared to the south site, resulting in higher mixing at the south site. Near the boundary, near-inertial to diurnal oscillations are more energetic at the north than the south site. This asymmetry is attributed to near-inertial internal waves that are generated north of the ridge by winter storms; the ridge shadows the equatorward-propagating near-inertial internal waves leading to negligible amplitudes on the southern lee side. The near-inertial waves combine with internal tidal motions to create high strain conditions that lead to mixing at the north site.

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“…There have also been many investigations of internal waves in fjords or lochs with sill (Stigebrandt and Aure 1989;Farmer and Freeland 1983;Lamb 2004;Vlasenko and Hutter 2002;Inall et al 2004;Cummins 2003;Davies and Xing 2007;Armi 1999, 2001;Klymak and Gregg 2004;Berntsen et al 2008;Davies 2006a, b, 2007). Many studies address internal motions in the ocean forced by wind (Nagasawa et al 2000;Alford 2001;Niwa and Hibiya 1997;Greatbatch 1984;Hibiya et al 2002;Plueddemann and Farrar 2006;Huang et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Numerical studies of wind forced internal waves with a nonhydrostatic model

Bergh

Berntsen

2009

Ocean Dynamics

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The nonhydrostatic pressure effects on the generation and propagation of wind-forced internal waves are studied with a two-dimensional numerical ocean model. A one-way directed wind pulse over a stratified ocean initiates surface and internal waves in a closed basin. The studies are performed with horizontal grid sizes in the range from 1 km to 62.5 m. The experiments are performed with both a hydrostatic and a nonhydrostatic model, facilitating systematic studies of the sensitivity of the numerical model results to the grid size and to the nonhydrostatic pressure adjustments. The results show that the nonhydrostatic pressure effects are highly dependent on the grid size and grow with increased resolution. In the internal depression wave, the horizontal nonhydrostatic pressure gradients reach the same order of magnitude as the hydrostatic gradients in the high-resolution nonhydrostatic studies. In these studies, the nonhydrostatic pressure gradients approximately balance the corresponding hydrostatic pressure gradients in the internal depression wave, and the wave degenerates into a train of soliton waves. The time for the soliton form to develop agrees with the steepening timescale calculated from Korteweg-de Vries theory. In the high-resolution hydrostatic model, the internal depression wave takes the form of a single wave front. When the internal waves are generated in the boundary layers, the nonhydrostatic pressure gradients are much smaller than the hydrostatic gradients and the generation processes are not effected by the nonhydrostatic pressure with the present range of grid sizes.

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Spatial and temporal distribution of the wind‐induced internal wave energy available for deep water mixing in the North Pacific

Cited by 79 publications

References 42 publications

Damping of inertial motions by parametric subharmonic instability in baroclinic currents

Damping of inertial motions by parametric subharmonic instability in baroclinic currents

Boundary Mixing Associated with Tidal and Near-Inertial Internal Waves

Numerical studies of wind forced internal waves with a nonhydrostatic model

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