Mechanisms for enhanced turbulence in the Drake Passage region of the Southern Ocean

Merrifield, Sophia

doi:10.1575/1912/8079

Cited by 1 publication

(4 citation statements)

References 110 publications

(249 reference statements)

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“…We tested boundary layer scalings (BLS) from satellite data against direct measurements of TKE dissipation rate from a glider. We found that BLS underestimates turbulent dissipation in the near-surface and overestimates turbulent dissipation below the near-surface, consistent with Merrifield (2016). The structure of this bias is consistent across wind speeds in the lower 90% of the AML, but strongly contingent on wind speed in the upper 10% of the AML.…”

Section: Discussionsupporting

confidence: 80%

“…5 for an example profile), consistent withMerrifield's (2016) bulk analysis of tow-yo VMP transects from DIMES US5.A section of this bias is shown in Fig.6c, with blue hues (red hues) indicating underprediction (overprediction) of turbulence in the surface boundary layer, with underprediction of near-surface TKE dissipation rates by up to 4 orders of magnitude. The vertical extent of this underprediction varies in depth, with three strong events lagging 2-3 days after intense storms; these will be revisited in the Discussion.…”

supporting

confidence: 76%

“…A second physical explanation is that sources of turbulent kinetic energy (TKE) other as internal wave driven mixing (St. Laurent et al, 2012) and double diffusion (Merrifield et al, 2016). It should be emphasized that this second explanation is not a complete explanation by itself because it does not account for the lack of observed turbulence at depth in Fig.…”

Section: B Influence Of Sources Other Than Breaking Wavesmentioning

confidence: 99%

“…However, there are several issues with this simplification, which neglects wave effects and boundary sources; in the real surface boundary layer, there is addition production due to Stokes shear, and neither variety of shear is necessarily aligned with the momentum flux ⟨𝑢𝑤⟩. Several past works have explored these additions (Agrawal et al, 1992;Sutherland et al, 2013;2014;2016;D'Asaro et al, 2014;Fox-Kemper et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

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Shear Turbulence in the High-Wind Southern Ocean Using Direct Measurements

Ferris

Clayson

Gong

et al. 2022

Journal of Physical Oceanography

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The ocean surface boundary layer is a gateway of energy transfer into the ocean. Wind-driven shear and meteorologically forced convection inject turbulent kinetic energy into the surface boundary layer, mixing the upper ocean and transforming its density structure. In the absence of direct observations or the capability to resolve sub-grid scale 3D turbulence in operational ocean models, the oceanography community relies on surface boundary layer similarity scalings (BLS) of shear and convective turbulence to represent this mixing. Despite their importance, near-surface mixing processes (and ubiquitous BLS representations of these processes) have been under-sampled in high energy forcing regimes such as the Southern Ocean. With the maturing of autonomous sampling platforms, there is now an opportunity to collect high-resolution spatial and temporal measurements in the full range of forcing conditions. Here, we characterize near-surface turbulence under strong wind forcing using the first long-duration glider microstructure survey of the Southern Ocean. We leverage these data to show that the measured turbulence is significantly higher than standard shear-convective BLS in the shallower parts of the surface boundary layer and lower than standard shear-convective BLS in the deeper parts of the surface boundary layer; the latter of which is not easily explained by present wave-effect literature. Consistent with the CBLAST (Coupled Boundary Layers and Air Sea Transfer) low winds experiment, this bias has the largest magnitude and spread in shallowest 10% of the actively mixing layer under low-wind and breaking wave conditions, when relatively low levels of turbulent kinetic energy (TKE) in surface regime are easily biased by wave events.

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Section: Discussionsupporting

confidence: 80%

supporting

confidence: 76%

Section: B Influence Of Sources Other Than Breaking Wavesmentioning

confidence: 99%