Radiation and Dissipation of Internal Waves Generated by Geostrophic Motions Impinging on Small-Scale Topography: Theory

The variability of the turbulent kinetic energy dissipation due to internal waves is quantified using a finescale parameterization applied to the A25 Greenland-Portugal transect repeated every two years from 2002 to 2012. The internal wave velocity shear and strain are estimated for each cruise at 91 stations from full depth vertical profiles of density and velocity. . The interannual variability in the dissipation rates is remarkably small over the whole transect. A few strong dissipation rate events exceeding the uncertainty of the finescale parameterization occur at depth between the Azores-Biscay Rise and Eriador Seamount. This region is also marked by mesoscale eddying flows resulting in enhanced surface energy level and enhanced bottom velocities. Estimates of the vertical energy fluxes into the internal tide and into topographic internal waves suggest that the latter are responsible for the strong dissipation events. At Eriador Seamount, both topographic internal waves and the internal tide contribute with the same order of magnitude to the dissipation rate while around the Reykjanes Ridge the internal tide provides the bulk of the dissipation rate.

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“…This dependence was confirmed by numerical simulations with Fr c 5 0.7 21 (Nikurashin and Ferrari 2010). In this study we chose Fr c 5 0.75 21 .…”

supporting

confidence: 57%

Variability of the Turbulent Kinetic Energy Dissipation along the A25 Greenland–Portugal Transect Repeated from 2002 to 2012

Ferron

Kokoszka

Mercier

et al. 2016

Journal of Physical Oceanography

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“…Fu et al, 2010), and investigating mechanisms for the damping of mesoscale eddies, such as radiation of Rossby waves, frontogenesis and lee internal waves (e.g. Flierl, 1984;Capet et al, 2008;Nikurashin and Ferrari, 2010).…”

Section: Research Problemsmentioning

confidence: 99%

Energy pathways and structures of oceanic eddies from the ECCO2 state estimate and simplified models

Chen¹

2013

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Studying oceanic eddies is important for understanding and predicting ocean circulation and climate variability. The central focus of this dissertation is the energy exchange between eddies and mean flow and banded structures in the low-frequency component of the eddy field. A combination of a realistic eddy-permitting ocean state estimate and simplified theoretical models is used to address the following specific questions. (1) What are the major spatial characteristics of eddy-mean flow interaction from an energy perspective? Is eddy-mean flow interaction a local process in most ocean regions? (2) The banded structures in the low-frequency eddy field are termed striations. How much oceanic variability is associated with striations? How does the time-mean circulation, for example a subtropical gyre or constant mean flow, influence the origin and characteristics of striations? How much do striations contribute to the energy budget and tracer mixing?

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“…These abyssal waters are exported northward into and across the ACC and, in the process, are transformed into mid-depth waters by small-scale, turbulent diabatic mixing. Ultimately, it is the intensity of this mixing that sets the rate at which the abyssal ocean overturns 8, 9,15 .Observations of the spatial distribution of turbulent mixing [16][17][18][19][20] and idealised modelling studies 15,21 link the occurrence of Southern Ocean abyssal mixing to the breaking of internal lee waves, generated as the ACC's vigorous mesoscale eddy flows impinge on seafloor topography. …”

mentioning

confidence: 99%

“…Observations of the spatial distribution of turbulent mixing [16][17][18][19][20] and idealised modelling studies 15,21 link the occurrence of Southern Ocean abyssal mixing to the breaking of internal lee waves, generated as the ACC's vigorous mesoscale eddy flows impinge on seafloor topography.…”

mentioning

confidence: 99%

“…The radiation and breaking of lee waves is estimated to account for the bulk of the dissipation of the Southern Ocean eddy field 21,22 , and to support a major fraction of the diabatic water mass transformation closing the lower overturning cell in the abyssal ocean 23 . This prompts the hypothesis that Southern Ocean abyssal mixing and overturning are sensitive to the intensity of the regional eddy field and, since the eddy field is primarily energised by instabilities of the windforced circulation 8,24,25 , to climatic perturbations in atmospheric forcing.…”

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confidence: 99%

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Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales

et al. 2014

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The Southern Ocean plays a pivotal role in global ocean circulation and climate [1][2][3] . It is there that the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths, forming two overturning cells that exchange large amounts of heat and carbon with the atmosphere [4][5][6] . While the climatic drivers of changes in the upper cell are relatively well established 7 , little is known about how the lower cell responds to changes in climatic forcing. Here, we show the first observational evidence that 1 small-scale mixing in the abyssal Southern Ocean, a major driver of the lower overturning cell [8][9][10] , exhibits variability on time scales of months to decades, consistent with a significant modulation by oceanic eddies impinging on seafloor topography. As the intensity of the regional eddy field is regulated by the Southern Hemisphere westerlies 11,12 , our findings suggest that Southern Ocean abyssal mixing and overturning are sensitive to climatic perturbations in wind forcing.The Southern Ocean limb of the global overturning circulation consists of two cells 4, 5,13 . The upper cell involves the upwelling and southward flow of mid-depth waters of North Atlantic origin, their transformation into lighter waters within the upper layers of the Antarctic Circumpolar Current (ACC), and their subsequent return northward as mode and intermediate waters. This vertical circulation is underpinned by a combination of wind-driven Ekman motions, eddy-induced flows, and air-sea interaction, which sustains the diabatic near-surface water mass transformation 4, 7,14 . In the lower cell, the southward shoaling of mid-depth waters is balanced by the production of dense abyssal waters by intense oceanic heat loss along the Antarctic margin. These abyssal waters are exported northward into and across the ACC and, in the process, are transformed into mid-depth waters by small-scale, turbulent diabatic mixing. Ultimately, it is the intensity of this mixing that sets the rate at which the abyssal ocean overturns 8, 9,15 .Observations of the spatial distribution of turbulent mixing [16][17][18][19][20] and idealised modelling studies 15,21 link the occurrence of Southern Ocean abyssal mixing to the breaking of internal lee waves, generated as the ACC's vigorous mesoscale eddy flows impinge on seafloor topography. 2The radiation and breaking of lee waves is estimated to account for the bulk of the dissipation of the Southern Ocean eddy field 21,22 , and to support a major fraction of the diabatic water mass transformation closing the lower overturning cell in the abyssal ocean 23 . This prompts the hypothesis that Southern Ocean abyssal mixing and overturning are sensitive to the intensity of the regional eddy field and, since the eddy field is primarily energised by instabilities of the windforced circulation 8,24,25 , to climatic perturbations in atmospheric forcing.We address this hypothesis by analysing the temporal variability of Southern Ocean abyssal mixing and inte...

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Radiation and Dissipation of Internal Waves Generated by Geostrophic Motions Impinging on Small-Scale Topography: Theory

Cited by 185 publications

References 38 publications

Variability of the Turbulent Kinetic Energy Dissipation along the A25 Greenland–Portugal Transect Repeated from 2002 to 2012

Variability of the Turbulent Kinetic Energy Dissipation along the A25 Greenland–Portugal Transect Repeated from 2002 to 2012

Energy pathways and structures of oceanic eddies from the ECCO2 state estimate and simplified models

Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales

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