Diapycnal Mixing and Internal Waves (original) (raw)
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Internal waves, finestructure, microstructure, and mixing in the ocean
Reviews of Geophysics, 1979
Progress in measuring• interpreting, and understanding oceanic internal gravity waves and fine and microstructure is reviewed; we emphasize the quadrennium 1975-1978. The context is how these subjects contribute to oceanic mixing. The overlap between the areas is examined, as is the relevance of the subjects to other aspects of oceanography.
Internal waves across the Pacific
Geophys. Res. …, 2007
1] The long-range propagation of the semidiurnal internal tide northward from the Hawaiian ridge and its susceptibility to parametric subharmonic instability (PSI) at the ''critical latitude,'' l c = 28.8°N, were examined in spring 2006 with intensive shipboard and moored observations spanning 25 -37°N along a tidal beam. Velocity and shear at l c were dominated by intense vertically-standing, inertially-rotating bands of several hundred meters vertical wavelength. These occurred in bursts following spring tide, contrasting sharply with the downward-propagating, wind-generated features seen at other latitudes. These marginally-stable layers (which have inverse 16-meter Richardson number Ri 16 À1 = 0.7) are interpreted as the inertial waves resulting from PSI of the internal tide. Elevated near-inertial energy and parameterized diapycnal diffusivity, and reduced asymmetry in upgoing/ downgoing energy, were also observed at and equatorward of l c . Yet, simultaneous moored measurements of semidiurnal energy flux and 1-km-deep velocity sections measured from the ship indicate that the internal tide propagates at least to 37°N, with no detectable energy loss or phase discontinuity at l c . Our observations indicate that PSI occurs in the ocean with sufficient intensity to substantially
2001
The long-term goal of our research is to identify and quantify key processes responsible for vertical and lateral mixing in oceans, which influences transports of heat, energy, momentum, dissolved matter and plankton in pelagic and littoral oceans. OBJECTIVES The main objective of the project is to conduct a comprehensive analysis of small and mesoscale phenomena, focusing on oceanic marginal zones. Mixing, internal waves and transformation of water masses were of major concern during the last year. We continued the development of a web-accessible database containing mooring and profiling measurements taken by Russian oceanographers in deep basins of the Atlantic, Pacific, and Indian oceans, at transAtlantic sections and in the marginal seas of western Pacific. Collection of new data pertinent to turbulent mixing in the near-surface boundary layers, both from oceanic and atmospheric sides, was an important part of our work. APPROACH We analyzed existing measurements on internal waves influenced by topography in deep ocean and near shelf breaks in conjunction with results from numerical simulations, studied the nature of fine structure in various waters of the equatorial Atlantic, and conducted new measurements of turbulence, thermohaline structure and currents in the North Atlantic in collaboration with Russian, Spanish, and Canadian scientists onboard of r/v Akademik Ioffe (Russian Academy of Sciences). This research cruises allowed obtaining of new CTD and ADCP measurements (Drs.
Eddy-Modulated Internal Waves and Mixing on a Midocean Ridge
Journal of Physical Oceanography, 2012
Mesoscale eddies are ubiquitous in the World Ocean and dominate the energy content on subinertial time scales. Recent theoretical and numerical studies suggest a connection between mesoscale eddies and diapycnal mixing in the deep ocean, especially near rough topography in regions of strong geostrophic flow. However, unambiguous observational evidence for such a connection has not yet been found, and it is still unclear what physical processes are responsible for transferring energy from mesoscale to small-scale processes. Here, the authors present observations demonstrating that finescale variability near the crest of the East Pacific Rise is strongly modulated by low-frequency geostrophic flows, including those due to mesoscale eddies. During times of strong subinertial flows, the authors observed elevated kinetic energy on vertical scales ,50 m and in the near-inertial band, predominantly upward-propagating near-inertial waves, and increased incidence of layers with Richardson number (Ri) , 1 /4. In contrast, during times of weak subinertial flows, kinetic energy in the finescale and near-inertial bands is lower, Ri values are higher, and near-inertial waves propagate predominantly downward through the water column. Diapycnal diffusivities estimated indirectly from a simple Ri-based parameterization are consistent with results from a tracer-release experiment and a microstructure survey bracketing the mooring measurements. These observations are consistent with energy transfer (a ''cascade'') from subinertial flows, including mesoscale eddies, to nearinertial oscillations, turbulence, and mixing. This interpretation suggests that, in addition to topographic roughness and tidal forcing, parameterization of deep-ocean mixing should also take subinertial flows into account. The findings presented here are expected to be useful for validating and improving numerical-model parameterizations of turbulence and mixing in the ocean.
Deep Sea Research Part I: Oceanographic Research Papers, 2007
From ADCP measurements in the thermocline over the continental slope of the Bay of Biscay the vertical variation of the contribution of the inertio-gravity waveband to the kinetic energy and variance of the current shear was analysed. The semi-diurnal tides together with near inertial waves appeared to provide over 70% of the high-frequency kinetic energy (> 1 / 3 cpd). Over the vertical range of the ADCP bins, about 400 M, the phase of the M2 tide changed up to 155°, showing the importance of the contribution of internal waves to the observed tidal motion. Both semi-diurnal internal tidal waves and near-inertial waves were organized in wave beams with a limited vertical extent, probably about 50 to 60% of the vertical wavelength. The relatively large shear in the inertio-gravity wave band, supported an annual mean gradient Richardson number well below 1, and was probably capable of maintaining turbulent mixing for a large part of the time.
Internal gravity waves in the upper eastern equatorial Pacific: Observations and numerical solutions
Journal of Geophysical Research, 1997
On the basis of data froxn a towed thermistor chain collected near 140øW on the equator during April 1987, the zonal wavenumber and vertical structure of internal gravity waves were observed to vary significantly between wave events. Our hypothesis is that this variability is due to changes in the vertical structure of mean horizontal velocity and density. Assuming that the observed waves were the fastest growing modes for shear instability, we solve the Taylor-Goldstein equation, using different analytical basic states, including a zonal and meridional flow, to simulate the different conditions during 4 nights of intense internal wave activity. We find that while the observed waves are of finite amplitude, linear sheeu' instability is sufficient to explain the wavelength and vertical structure of vertical displacement for most of the waves. The fastest growing, unstable, mode-one solutions have e-folding growth times of less than 10 min. These solutions show wave phase speeds and vertical structures to be highly dependent upon the velocity structure of the uppermost 40 m. Near the base of the mixed layer at a flow inflection point the kinetic energy of the mean flow is extracted for wave growth. Wave vertical displacement is maximum near this inflection point. Zonal phase speeds range from-0.8 to-0.1 m/s. The propagation direction of waves with growth rates of 75% of the maximum growth rate can range from about 45 ø north to 45 • south of the zonal direction. The vertical wave-induced Reynolds stress divergence could explain a discrepancy in zonal momentum budgets of the upper 90 m of this region. Estimates of this stress divergence show that only about 100 days of intense internal wave activity is needed per year for these internal waves to explain estimated residuals of the mean zonal momentum budgets of this region at 50-to 100-m depth. eral mechanisms for this diurnal cycling have been considered, including diurnal cycles in solar heating, surface wind stress, and mean velocity shears, only internal waves can account for the cycle in turbulence extending well below the mixed layer. Indeed, the correspondence of the deeper mixing with the presence of internal waves subsequently was confirmed by two sets of independent observations. The first, a towed thermistor chain [
From Topographic Internal Gravity Waves to Turbulence
Annual Review of Fluid Mechanics, 2017
Internal gravity waves are a key process linking the large-scale mechanical forcing of the oceans to small-scale turbulence and mixing. In this review, we focus on internal waves generated by barotropic tidal flow over topography. We review progress made in the past decade toward understanding the different processes that can lead to turbulence during the generation, propagation, and reflection of internal waves and how these processes affect mixing. We consider different modeling strategies and new tools that have been developed. Simulation results, the wealth of observational material collected during large-scale experiments, and new laboratory data reveal how the cascade of energy from tidal flow to turbulence occurs through a host of nonlinear processes, including intensified boundary flows, wave breaking, wave-wave interactions, and the instability of high-mode internal wave beams. The roles of various nondimensional parameters involving the ocean state, roughness geometry, and...
Internal-inertial waves and crossfrontal circulation in the upper ocean
Física de la Tierra, 1991
Se estudia el proceso de ajuste entre des masas de agua de propiedades diferentes y la circulación secundaría asociada, por medio de un modelo oceánico tridimensional de ecuaciones primitivas. En particular, se investiga la recirculación y el movimiento vertical cerca de un ...
Internal waves, solitary-like waves, and mixing on the Monterey Bay shelf
Continental Shelf Research, 2005
Microstructure measurements taken on the Monterey Bay continental shelf, within 4 km of the shelf break, reveal a complex mixing environment. Depth-and time-averaged dissipation rates ð ¼ 7:4255:8 Â 10 À9 W kg À1 Þ and diapycnal diffusivities ðK r ¼ 6:1237:8 Â 10 À5 m 2 s À1 Þ were elevated above observations made over other continental shelves with no significant topography, but were below those influenced by topographic features. The close proximity of the shelf break/canyon rim, locally generated internal tides, and nonlinear internal waves all contributed to the elevated turbulence. The complex bathymetry associated with Monterey Submarine Canyon allowed an internal tide to be generated at depths greater than 1500 m, as well as at the shelf break. The observed velocity field was normally dominated by upward energy propagation from the local shelf break generated internal tide, but near low tide downward energy propagation from a surface reflection of the internal tide generated below 1500 m was observed. Turbulent dissipation rates were not well parameterized by either the open-ocean Gregg-Henyey model or the recently developed MacKinnon-Gregg shelf model. Like its application on the New England shelf, the MacKinnon-Gregg model had the correct functional dependence on shear and stratification (dissipation increasing with increasing shear and increasing stratification), however, the magnitude and range of values were too small. The most surprising finding was the presence of what we believe to be large, high-aspect-ratio, downslope-propagating nonlinear internal solitarylike waves of elevation. Upon reaching the canyon rim, these waves propagated into deep water and transformed into waves of depression. On the shelf south of the canyon, the waves of elevation accounted for 20% of the observed turbulent kinetic energy dissipation. Off the shelf, where the solitary-like waves changed to downward displacement, 0278-4343/$ -see front matter r (R.-C. Lien). their average dissipation increased 10-fold to ¼ 2:6 Â 10 À6 W kg À1 , and accounted for nearly half the dissipation in the upper 150 m. r
A breaking internal wave in the surface ocean boundary layer
Journal of Geophysical Research: Oceans, 2015
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