Mixing Rates and Bottom Drag in Bering Strait

Couto, Nicole; Alford, Matthew H.; MacKinnon, Jennifer A.; Mickett, John B.

doi:10.1175/jpo-d-19-0154.1

Cited by 4 publications

(8 citation statements)

References 67 publications

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“…If we force a linear relation in panel (a), we find a drag coefficient of C d = 8.2×10 −4 . This value is comparable to but smaller than the typical range of bottom drag values of (1-3) × 10 −3 and the bottom drag deduced from in situ observations in Bering Strait of 2.3 × 10 −3 (Couto et al, 2020). The red data points in Fig.…”

Section: Tidal Mixingsupporting

confidence: 51%

“…Heat loss resulting from vertical heat fluxes contributes to the heat loss to the atmosphere and to the deep ocean, but not to the lateral heat loss. Several processes can lead to lateral heat loss north of Svalbard, including eddy spreading from the slope into the basin (Crews et al, 2018;Våge et al, 2016). Using eddy-resolving regional model results, Crews et al (2018) found that eddies export 1.0 TW out of the boundary current, delivering heat into the interior Arctic Ocean at an average rate of ∼ 15 W m −2 .…”

Section: Atlantic Water Heat Lossmentioning

confidence: 99%

“…Several processes can lead to lateral heat loss north of Svalbard, including eddy spreading from the slope into the basin (Crews et al, 2018;Våge et al, 2016). Using eddy-resolving regional model results, Crews et al (2018) found that eddies export 1.0 TW out of the boundary current, delivering heat into the interior Arctic Ocean at an average rate of ∼ 15 W m −2 . West of Svalbard, found that the measured turbulent heat flux in the WSC was too small to account for the cooling rate of the Atlantic Water layer but reported a substantial contribution from energetic convective mixing of an unstable bottom boundary layer on the slope.…”

Section: Atlantic Water Heat Lossmentioning

confidence: 99%

“…Cooling and freshening of the Atlantic Water north of Svalbard result from different processes. Along the slope north of Svalbard, eddies are shed from the Atlantic Water Boundary Current (Våge et al, 2016;Crews et al, 2018), transporting 0.16 Sv (1 Sv = 10 6 m 3 s −1 ) of Atlantic Water and 1.0 TW (1 TW = 10 12 W) away from the boundary current. Large vertical turbulent fluxes can occur in localized regions.…”

Section: Introductionmentioning

confidence: 99%

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Structure and drivers of ocean mixing north of Svalbard in summer and fall 2018

Koenig¹,

Kolås²,

Fer³

2020

Preprint

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Abstract. Ocean mixing in the Arctic Ocean cools and freshens the Atlantic and Pacific-origin waters by mixing them with surrounding waters, which has major implications on global scale as the Arctic Ocean is a main sink for heat and salt. We investigate the drivers of ocean mixing north of Svalbard, in the Atlantic sector of the Arctic, based on observations collected during two research cruises in summer and fall 2018. In the mixed layer, there is a nonlinear relation between the layer-integrated dissipation and wind energy input; convection was active at a few stations and was responsible for enhanced turbulence compare to what was expected from the wind work alone. Summer melting of sea ice reduces the temperature, salinity and depth of the mixed layer, and increases salt and buoyancy fluxes at the base of the mixed layer. Deeper in the water column and near the seabed, tidal work is a main source of turbulence: diapycnal diffusivity in the bottom 250 m of the water column is enhanced during strong tidal currents, reaching on average 10−3 m2 s−1. The average profile of diffusivity decays with distance from seabed with an e-folding scale of 22 m compared to 18 m in conditions with weaker tidal currents. A nonlinear relation is inferred between the depth-integrated dissipation in the bottom 250 m of the water column and the tidally-driven bottom drag and is used to estimate the bottom dissipation along the continental slope of the Eurasian Basin. Computation of the inverse Froude number suggests that nonlinear internal waves forced by the diurnal tidal activity (K1 constituent) can develop north of Svalbard and in the Laptev and Kara Seas, with the potential to mix the entire water column vertically. Estimates of vertical turbulent heat flux from the Atlantic Water layer up to the mixed layer reaches 30 W m−2 in the core of the boundary current, and is on average 8 W m−2, accounting for ∼ 1 % of the total heat loss of the Atlantic layer in the region.

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Section: Tidal Mixingsupporting

confidence: 51%

Section: Atlantic Water Heat Lossmentioning

confidence: 99%

Section: Atlantic Water Heat Lossmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Structure and drivers of ocean mixing north of Svalbard in summer and fall 2018

Koenig¹,

Kolås²,

Fer³

2020

Preprint

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“…In practice, however, our method is different from Dewey and Crawford (1988). We determine the values of u ⋆ using a least-squares fit to ɛ, similar to Couto et al (2020).…”

Section: Friction Velocity Estimatesmentioning

confidence: 99%

Upper‐Ocean Turbulence Structure and Ocean‐Ice Drag Coefficient Estimates Using an Ascending Microstructure Profiler During the MOSAiC Drift

et al. 2022

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Sea ice mediates the transfer of momentum, heat, and gas between the atmosphere and the ocean. However, the under‐ice boundary layer is not sufficiently constrained by observations. During the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC), we collected profiles in the upper 50–80 m using a new ascending vertical microstructure profiler, resolving the turbulent structure within 1 m to the ice. We analyzed 167 dissipation rate profiles collected between February and mid‐September 2020, from 89°N to 79°30′N through the Amundsen Basin, Nansen Basin, Yermak Plateau, and Fram Strait. Measurements covered a broad range of forcing (0–15 m s−1 wind and 0–0.4 m s−1 drift speeds) and sea ice conditions (pack ice, thin ice, and leads). Dissipation rates varied by over 4 orders of magnitude from 10−9 W kg−1 below 40 m to above 10−5 W kg−1 at 1 m. Following wind events, layers with dissipation scriptO()10−6 $\mathcal{O}\left(1{0}^{-6}\right)$ W kg−1 extended down to 20 m depth under pack ice. In leads in the central Arctic, turbulence was enhanced 2–10 times relative to thin ice profiles. Under‐ice dissipation profiles allowed us to estimate the boundary layer thickness (4 ± 2 m), and the friction velocity (1–15 mm s−1, 4.7 mm s−1 on average). A representative range of drag coefficient for the MOSAiC sampling site was estimated to (4–6) × 10−3, which is a typical value for Arctic floe observations. The average ratio of drift speed to wind speed was close to the free‐drift ratio of 2% with no clear seasonal or regional variability.

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From a vortex gas to a vortex crystal in instability-driven two-dimensional turbulence

van Kan,

Favier,

Julien

et al. 2024

J. Fluid Mech.

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We study structure formation in two-dimensional turbulence driven by an external force, interpolating between linear instability forcing and random stirring, subject to nonlinear damping. Using extensive direct numerical simulations, we uncover a rich parameter space featuring four distinct branches of stationary solutions: large-scale vortices, hybrid states with embedded shielded vortices (SVs) of either sign, and two states composed of many similar SVs. Of the latter, the first is a dense vortex gas where all SVs have the same sign and diffuse across the domain. The second is a hexagonal vortex crystal forming from this gas when the linear instability is sufficiently weak. These solutions coexist stably over a wide parameter range. The late-time evolution of the system from small-amplitude initial conditions is nearly self-similar, involving three phases: initial inverse cascade, random nucleation of SVs from turbulence and, once a critical number of vortices is reached, a phase of explosive nucleation of SVs, leading to a statistically stationary state. The vortex gas is continued in the forcing parameter, revealing a sharp transition towards the crystal state as the forcing strength decreases. This transition is analysed in terms of the diffusivity of individual vortices using ideas from statistical physics. The crystal can also decay via an inverse cascade resulting from the breakdown of shielding or insufficient nonlinear damping acting on SVs. Our study highlights the importance of the forcing details in two-dimensional turbulence and reveals the presence of non-trivial SV states in this system, specifically the emergence and melting of a vortex crystal.

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Mixing Rates and Bottom Drag in Bering Strait

Cited by 4 publications

References 67 publications

Structure and drivers of ocean mixing north of Svalbard in summer and fall 2018

Structure and drivers of ocean mixing north of Svalbard in summer and fall 2018

Upper‐Ocean Turbulence Structure and Ocean‐Ice Drag Coefficient Estimates Using an Ascending Microstructure Profiler During the MOSAiC Drift

From a vortex gas to a vortex crystal in instability-driven two-dimensional turbulence

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