Influence of the Distortion of Vertical Wavenumber Spectra on Estimates of Turbulent Dissipation using the Finescale Parameterization: Eikonal Calculations

2021 ◽  
Author(s):  
ANNE TAKAHASHI ◽  
TOSHIYUKI HIBIYA ◽  
ALBERTO C. NAVEIRA GARABATO
Keyword(s):  
Internal Wave ◽  
Wave Energy ◽  
Mesoscale Eddy ◽  
Wave Interaction ◽  
Interaction Theory ◽  
Turbulent Dissipation ◽  
Energy Cascades ◽  
Circumpolar Current ◽  
Noise Contamination ◽  
The Antarctic

AbstractThe finescale parameterization, formulated on the basis of a weak nonlinear wave–wave interaction theory, is widely used to estimate the turbulent dissipation rate, ε. However, this parameterization has previously been found to overestimate ε in the Antarctic Circumpolar Current (ACC) region. One possible reason for this overestimation is that vertical wavenumber spectra of internal wave energy are distorted from the canonical Garrett-Munk spectrum and have a spectral “hump” at low vertical wavenumbers. Such distorted vertical wavenumber spectra were also observed in other mesoscale eddy-rich regions. In this study, using eikonal simulations, in which internal wave energy cascades are evaluated in the frequency-wavenumber space, we examine how the distortion of vertical wavenumber spectra impacts on the accuracy of the finescale parameterization. It is shown that the finescale parameterization overestimates ε for distorted spectra with a low-vertical-wavenumber hump because it incorrectly takes into account the breaking of these low-vertical-wavenumber internal waves. This issue is exacerbated by estimating internal wave energy spectral levels from the low-wavenumber band rather than from the high-wavenumber band, which is often contaminated by noise in observations. Thus, in order to accurately estimate the distribution of ε in eddy-rich regions like the ACC, high-vertical-wavenumber spectral information free from noise contamination is indispensable.

scholarly journals Internal Waves and Turbulence in the Antarctic Circumpolar Current

2013 ◽  
Vol 43 (2) ◽  
pp. 259-282 ◽  
Author(s):  
Stephanie Waterman ◽  
Alberto C. Naveira Garabato ◽  
Kurt L. Polzin
Keyword(s):  
Internal Wave ◽  
Wave Field ◽  
Dissipation Rate ◽  
Antarctic Circumpolar Current ◽  
Wave Radiation ◽  
Turbulent Dissipation ◽  
Internal Wave Field ◽  
Diapycnal Diffusivity ◽  
Circumpolar Current ◽  
The Antarctic

Abstract This study reports on observations of turbulent dissipation and internal wave-scale flow properties in a standing meander of the Antarctic Circumpolar Current (ACC) north of the Kerguelen Plateau. The authors characterize the intensity and spatial distribution of the observed turbulent dissipation and the derived turbulent mixing, and consider underpinning mechanisms in the context of the internal wave field and the processes governing the waves’ generation and evolution. The turbulent dissipation rate and the derived diapycnal diffusivity are highly variable with systematic depth dependence. The dissipation rate is generally enhanced in the upper 1000–1500 m of the water column, and both the dissipation rate and diapycnal diffusivity are enhanced in some places near the seafloor, commonly in regions of rough topography and in the vicinity of strong bottom flows associated with the ACC jets. Turbulent dissipation is high in regions where internal wave energy is high, consistent with the idea that interior dissipation is related to a breaking internal wave field. Elevated turbulence occurs in association with downward-propagating near-inertial waves within 1–2 km of the surface, as well as with upward-propagating, relatively high-frequency waves within 1–2 km of the seafloor. While an interpretation of these near-bottom waves as lee waves generated by ACC jets flowing over small-scale topographic roughness is supported by the qualitative match between the spatial patterns in predicted lee wave radiation and observed near-bottom dissipation, the observed dissipation is found to be only a small percentage of the energy flux predicted by theory. The mismatch suggests an alternative fate to local dissipation for a significant fraction of the radiated energy.

scholarly journals Suppression of Internal Wave Breaking in the Antarctic Circumpolar Current near Topography

2014 ◽  
Vol 44 (5) ◽  
pp. 1466-1492 ◽  
Author(s):  
Stephanie Waterman ◽  
Kurt L. Polzin ◽  
Alberto C. Naveira Garabato ◽  
Katy L. Sheen ◽  
Alexander Forryan
Keyword(s):  
Internal Wave ◽  
Wave Field ◽  
Antarctic Circumpolar Current ◽  
Energy Dissipation Rate ◽  
Background Flow ◽  
Energy Propagation ◽  
Topographic Roughness ◽  
Flow Speeds ◽  
Circumpolar Current ◽  
The Antarctic

Abstract Simultaneous full-depth microstructure measurements of turbulence and finestructure measurements of velocity and density are analyzed to investigate the relationship between turbulence and the internal wave field in the Antarctic Circumpolar Current. These data reveal a systematic near-bottom overprediction of the turbulent kinetic energy dissipation rate by finescale parameterization methods in select locations. Sites of near-bottom overprediction are typically characterized by large near-bottom flow speeds and elevated topographic roughness. Further, lower-than-average shear-to-strain ratios indicative of a less near-inertial wave field, rotary spectra suggesting a predominance of upward internal wave energy propagation, and enhanced narrowband variance at vertical wavelengths on the order of 100 m are found at these locations. Finally, finescale overprediction is typically associated with elevated Froude numbers based on the near-bottom shear of the background flow, and a background flow with a systematic backing tendency. Agreement of microstructure- and finestructure-based estimates within the expected uncertainty of the parameterization away from these special sites, the reproducibility of the overprediction signal across various parameterization implementations, and an absence of indications of atypical instrument noise at sites of parameterization overprediction, all suggest that physics not encapsulated by the parameterization play a role in the fate of bottom-generated waves at these locations. Several plausible underpinning mechanisms based on the limited available evidence are discussed that offer guidance for future studies.

Global Abyssal Mixing Inferred from Lowered ADCP Shear and CTD Strain Profiles

2006 ◽  
Vol 36 (8) ◽  
pp. 1553-1576 ◽  
Author(s):  
Eric Kunze ◽  
Eric Firing ◽  
Julia M. Hummon ◽  
Teresa K. Chereskin ◽  
Andreas M. Thurnherr
Keyword(s):  
Internal Wave ◽  
Wave Spectrum ◽  
Wave Interaction ◽  
Deep Ocean ◽  
Eddy Diffusivity ◽  
Small Scale ◽  
Tidal Dissipation ◽  
Turbulent Dissipation ◽  
Active Turbulence ◽  
Parametric Subharmonic Instability

Abstract Internal wave–wave interaction theories and observations support a parameterization for the turbulent dissipation rate ɛ and eddy diffusivity K that depends on internal wave shear 〈Vz2〉 and strain 〈ξz2〉 variances. Its latest incarnation is applied to about 3500 lowered ADCP/CTD profiles from the Indian, Pacific, North Atlantic, and Southern Oceans. Inferred diffusivities K are functions of latitude and depth, ranging from 0.03 × 10−4 m2 s−1 within 2° of the equator to (0.4–0.5) × 10−4 m2 s−1 at 50°–70°. Diffusivities K also increase with depth in tropical and subtropical waters. Diffusivities below 4500-m depth exhibit a peak of 0.7 × 10−4 m2 s−1 between 20° and 30°, latitudes where semidiurnal parametric subharmonic instability is expected to be active. Turbulence is highly heterogeneous. Though the bulk of the vertically integrated dissipation ∫ɛ is contributed from the main pycnocline, hotspots in ∫ɛ show some correlation with small-scale bottom roughness and near-bottom flow at sites where strong surface tidal dissipation resulting from tide–topography interactions has been implicated. Average vertically integrated dissipation rates are 1.0 mW m−2, lying closer to the 0.8 mW m−2 expected for a canonical (Garrett and Munk) internal wave spectrum than the global-averaged deep-ocean surface tide loss of 3.3 mW m−2.

scholarly journals Turbulence and Diapycnal Mixing in Drake Passage

2012 ◽  
Vol 42 (12) ◽  
pp. 2143-2152 ◽  
Author(s):  
L. St. Laurent ◽  
A. C. Naveira Garabato ◽  
J. R. Ledwell ◽  
A. M. Thurnherr ◽  
J. M. Toole ◽  
...  
Keyword(s):  
Drake Passage ◽  
Global Ocean ◽  
Mixing Enhancement ◽  
Turbulent Dissipation ◽  
Dissipation Rates ◽  
Direct Measurements ◽  
Order Of Magnitude ◽  
Frontal Zones ◽  
Circumpolar Current ◽  
The Antarctic

Abstract Direct measurements of turbulence levels in the Drake Passage region of the Southern Ocean show a marked enhancement over the Phoenix Ridge. At this site, the Antarctic Circumpolar Current (ACC) is constricted in its flow between the southern tip of South America and the northern tip of the Antarctic Peninsula. Observed turbulent kinetic energy dissipation rates are enhanced in the regions corresponding to the ACC frontal zones where strong flow reaches the bottom. In these areas, turbulent dissipation levels reach 10−8 W kg−1 at abyssal and middepths. The mixing enhancement in the frontal regions is sufficient to elevate the diapycnal turbulent diffusivity acting in the deep water above the axis of the ridge to 1 × 10−4 m2 s−1. This level is an order of magnitude larger than the mixing levels observed upstream in the ACC above smoother bathymetry. Outside of the frontal regions, dissipation rates are O(10−10) W kg−1, comparable to the background levels of turbulence found throughout most mid- and low-latitude regions of the global ocean.

scholarly journals Mesoscale Eddy–Internal Wave Coupling. Part II: Energetics and Results from PolyMode

2010 ◽  
Vol 40 (4) ◽  
pp. 789-801 ◽  
Author(s):  
Kurt L. Polzin
Keyword(s):  
Transfer Coefficient ◽  
Internal Wave ◽  
Energy Budget ◽  
Wave Energy ◽  
Horizontal Transfer ◽  
Mesoscale Eddy ◽  
Wave Coupling ◽  
Vertical Transfer ◽  
Eddy Field

Abstract The issue of internal wave–mesoscale eddy interactions is revisited. Previous observational work identified the mesoscale eddy field as a possible source of internal wave energy. Characterization of the coupling as a viscous process provides a smaller horizontal transfer coefficient than previously obtained, with vh ≅ 50 m2 s−1 in contrast to νh ≅ 200–400 m2 s−1, and a vertical transfer coefficient bounded away from zero, with νυ + ( f 2/N 2)Kh ≅ 2.5 ± 0.3 × 10−3 m2 s−1 in contrast to νυ + ( f 2/N 2)Kh = 0 ± 2 × 10−2 m2 s−1. Current meter data from the Local Dynamics Experiment of the PolyMode field program indicate mesoscale eddy–internal wave coupling through horizontal interactions (i) is a significant sink of eddy energy and (ii) plays an O(1) role in the energy budget of the internal wave field.

scholarly journals Damping of climate-scale oceanic variability by mesoscale eddy turbulence

2020 ◽  
Author(s):  
F. Sévellec ◽  
A. C. Naveira Garabato ◽  
T. Huck
Keyword(s):  
Large Scale ◽  
Climatic Variability ◽  
Baroclinic Instability ◽  
Mesoscale Eddy ◽  
Drake Passage ◽  
Circumpolar Current ◽  
Climate Scale ◽  
The Antarctic ◽  
The Impact

AbstractThe impact of mesoscale eddy turbulence on long-term, climatic variability in the ocean's buoyancy structure is investigated using observations from a mooring deployed in the Drake Passage, Southern Ocean. By applying the Temporal-Residual-Mean framework and characterizing the variance contributors and the buoyancy variance budget, we identify the main source and sink of long-term buoyancy variance. Long-term buoyancy variance amplitude is set by long-term vertical velocity fluctuations acting on the steady stratification. This baro-clinic buoyancy flux is also the main source of the variance, indicative of the effect of large-scale baroclinic instability. This source is balanced by a sink of long-term buoyancy variance associated with the vertical advection of the steady stratification by the eddy-induced circulation. We conclude that mesoscale eddy turbulence acts as a damping mechanism for long-term, climatic variability in the region of the observations, consistent with an `eddy saturated' behaviour of the Antarctic Circumpolar Current.

scholarly journals Eddy-Induced Modulation of Turbulent Dissipation over Rough Topography in the Southern Ocean

2013 ◽  
Vol 43 (11) ◽  
pp. 2288-2308 ◽  
Author(s):  
J. Alexander Brearley ◽  
Katy L. Sheen ◽  
Alberto C. Naveira Garabato ◽  
David A. Smeed ◽  
Stephanie Waterman
Keyword(s):  
Southern Ocean ◽  
Internal Wave ◽  
Ocean Circulation ◽  
Wave Energy ◽  
Bottom Topography ◽  
Temporal Correlation ◽  
Drake Passage ◽  
Wave Radiation ◽  
Bottom Current ◽  
Turbulent Dissipation

Abstract Mesoscale eddies are universal features of the ocean circulation, yet the processes by which their energy is dissipated remain poorly understood. One hypothesis argues that the interaction of strong geostrophic flows with rough bottom topography effects an energy transfer between eddies and internal waves, with the breaking of these waves causing locally elevated dissipation focused near the sea floor. This study uses hydrographic and velocity data from a 1-yr mooring cluster deployment in the Southern Ocean to test this hypothesis. The moorings were located over a small (~10 km) topographic obstacle to the east of Drake Passage in a region of high eddy kinetic energy, and one was equipped with an ADCP at 2800-m depth from which internal wave shear variance and dissipation rates were calculated. Examination of the ADCP time series revealed a predominance of upward-propagating internal wave energy and a significant correlation (r = 0.45) between shear variance levels and subinertial near-bottom current speeds. Periods of strong near-bottom flow coincided with increased convergence of eddy-induced interfacial form stress in the bottom 1500 m. Predictions of internal wave energy radiation were made from theory using measured near-bottom current speeds, and the mean value of wave radiation (5.3 mW m−2) was sufficient to support the dissipated power calculated from the ADCP. A significant temporal correlation was also observed between radiated and dissipated power. Given the ubiquity of strong eddy flows and rough topography in the Southern Ocean, the transfer from eddy to internal wave energy is likely to be an important term in closing the ocean energy budget.

Irregular wave interaction with an offshore OWC wave energy converter

2021 ◽  
Vol 222 ◽  
pp. 108619
Author(s):  
Milad Zabihi ◽  
Said Mazaheri ◽  
Masoud Montazeri Namin ◽  
Ahmad Rezaee Mazyak
Keyword(s):  
Wave Energy ◽  
Wave Interaction ◽  
Wave Energy Converter ◽  
Energy Converter ◽  
Irregular Wave
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