On the Structure and Dynamics of the Oceanic Bottom Boundary Layer

Weatherly, Georges L.; Martin, Paul J.

doi:10.1175/1520-0485(1978)008<0557:otsado>2.0.co;2

Cited by 246 publications

(198 citation statements)

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“…With this definition, a cross-shelf spatial pattern emerged with bottom mixed layer heights ranging from 4-18 m on the shelf, a minimum at the foot of the front, and increasing to 40 m on the upper slope. Houghton (1995) found reasonable comparison between bottom mixed layer estimates with Weatherly and Martin's (1978) scaling. However, he found smaller bottom mixed layer heights than predicted from Lentz's (1991) scaling.…”

Section: Downstream Of This Location At Approximately 74mentioning

confidence: 65%

“…Ekman flows that has been examined in 1d models (Weatherly and Martin 1978. Although this asymmetry is shown to arise with state-dependent mixing schemes for 1d upwelling and downwelling flows, the important question to address in future studies is how the cross-isobath structure of the Ekman flow is modified by mixing during the buoyancy shutdown process.…”

Section: Discussionmentioning

confidence: 99%

“…Over a flat bottom, Weatherly and Martin (1978) argued on dimensional grounds that stratification reduces the bottom boundary layer height from the unstratified case. By including stratification in the scaling for the frictional boundary layer height, they showed that the revised stratified scale height was qualitatively consistent with previous estimates of bottom boundary layer thickness over the West Florida continental shelf (Weatherly and Van Leer 1977).…”

Section: Bottom Boundary Layers Over Continental Shelves and Upper Comentioning

confidence: 99%

“…Weatherly and Van Leer (1977) also suggested that patterns of warming (cooling) within the bottom boundary layer may be explained by frictionally driven downslope (upslope) flows due to downwelling (upwelling) favorable along-shelf flows. Weatherly and Martin (1978) used a numerical model, with the Mellor-Yamada level 2 turbulence closure scheme, to examine how the frictional bottom boundary layer is modified by upslope or downslope Ekman advection of buoyancy. The thickness of the bottom boundary layer is specified by the height at which the turbulence vanishes away from the bottom.…”

Section: Bottom Boundary Layers Over Continental Shelves and Upper Comentioning

confidence: 99%

“…First, Houghton (1995) examined data from the Shelf Edge Exchange Processes (SEEP-II) experiment to calculate bottom mixed layer heights near the front. Then, these heights were compared to both Weatherly and Martin's (1978) scaling for the height of the bottom boundary layer from a one-dimensional model of flow over a stratified flat bottom and Trowbridge and scaling for the height of the bottom mixed layer subject to a downslope Ekman buoyancy flux. From ADCP velocity data onshore of the shelfbreak, calculations of veering angles above the bottom are predominantly positive, consistent with an Ekman flow.…”

Section: Downstream Of This Location At Approximately 74mentioning

confidence: 99%

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Linear and nonlinear stratified spindown over sloping topography

Benthuysen¹

2010

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In a stratified rotating fluid, frictionally driven circulations couple with the buoyancy field over sloping topography. Analytical and numerical methods are used to quantify the impact of this coupling on the vertical circulation, spindown of geostrophic flows, and the formation of a shelfbreak jet.Over a stratified slope, linear spindown of a geostrophic along-isobath flow induces cross-isobath Ekman flows. Ekman advection of buoyancy weakens the vertical circulation and slows spindown. Upslope (downslope) Ekman flows tend to inject (remove) potential vorticity into (from) the ocean. Momentum advection and nonlinear buoyancy advection are examined in setting asymmetries in the vertical circulation and the vertical relative vorticity field. During nonlinear homogeneous spindown over a flat bottom, momentum advection weakens Ekman pumping and strengthens Ekman suction, while cyclonic vorticity decays faster than anticyclonic vorticity. During nonlinear stratified spindown over a slope, nonlinear advection of buoyancy enhances the asymmetry in Ekman pumping and suction, whereas anticyclonic vorticity can decay faster than cyclonic vorticity outside of the boundary layers.During the adjustment of a spatially uniform geostrophic current over a shelfbreak, coupling between the Ekman flow and the buoyancy field generates Ekman pumping near the shelfbreak, which leads to the formation of a jet. Scalings are presented for the upwelling strength, the length scale over which it occurs, and the timescale for jet formation. The results are applied to the Middle Atlantic Bight shelfbreak.

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Section: Downstream Of This Location At Approximately 74mentioning

confidence: 65%

Section: Discussionmentioning

confidence: 99%

Section: Bottom Boundary Layers Over Continental Shelves and Upper Comentioning

confidence: 99%

Section: Bottom Boundary Layers Over Continental Shelves and Upper Comentioning

confidence: 99%

Section: Downstream Of This Location At Approximately 74mentioning

confidence: 99%

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Linear and nonlinear stratified spindown over sloping topography

Benthuysen¹

2010

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Convective and shear-induced turbulence in the deep Kane Gap

Haren

Morozov

Gostiaux

et al. 2013

J. Geophys. Res. Oceans

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[1] The boundary layer above a 4569 m deep slope in the near-equatorial N-Atlantic Ocean Kane Gap, a throughflow for Antarctic Bottom Water (AABW), is characterized by two distinct turbulent regimes that differ by an order of magnitude in intensity depending on the direction of throughflow. During southward and downward flow, vertical mixing is vigorous. This is inferred from high-resolution temperature observations between 6 and 132 m above the bottom. For a representative case study of 2 days, average values are found for dissipation rate of " ¼ 2.1 6 1 Â 10 À9 W kg À1 and eddy diffusivity of K z ¼ 7 6 4 Â 10 À4 m 2 s À1 . The mixing is across relatively large vertical overturns. During northward and upward flow, smaller overturns are more horizontal as in stratified shear flow (with representative 2 day mean " ¼ 6 6 3 Â 10 À11 W kgStratification is approximately the same during both flow directions. Although the different turbulence regimes are partially associated with frictional boundary layers of large-scale flows above sloping topography, but not with those over flat bottoms, and partially with flow across a hill-promontory, internal waves are a dominant process in promoting turbulence. In addition, internal waves are observed to push stratification toward the bottom thereby importantly contributing to the mixing of AABW.

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Logarithmic velocity structure in the deep hypolimnetic waters of Lake Michigan

et al. 2016

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The characteristics of the bottom boundary layer are reported from a Lake Michigan field study carried out in deep hypolimnetic waters (55 m depth) during the stratified period (June–September 2012). The sandy substrate at the measurement site was densely covered with invasive quagga mussels (mean size: 1.6 cm; mean density: 10,000 mussels m−2). The measurements reveal a sluggish, compact bottom boundary layer, with flow speeds at 1 mab less than 5 cm s−1 for most of the period, and a dominance of subinertial energy. A downwelling event caused the largest currents observed during the deployment (10 cm s−1 at 1 mab) and a logarithmic layer thickness of 15 m. In spite of the weak flow, logarithmic profile fitting carried out on high‐resolution, near‐bed velocity profiles show consistent logarithmic structure (90% of profiles). Flow was dominated by subinertial energy but strong modified by near‐inertial waves. Fitted drag coefficients and roughness values are Cd1m = 0.004 and z0 = 0.12 cm, respectively. These values increase with decreasing flow speed, but approach canonical values for 1 mab flow speeds exceeding 4 cm s−1. The estimated vertical extent of the logarithmic region was compact, with a mean value of 1.2 m and temporal variation that is reasonably described by Ekman scaling, 0.07 u* / f, and the estimated overall Ekman layer thickness was generally less than 10 m. Near‐bed dissipation rates inferred from the law of the wall were 10−8−10−7 W kg−1 and turbulent diffusivities were 10−4−10−3 m2s−1.

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On the Structure and Dynamics of the Oceanic Bottom Boundary Layer

Cited by 246 publications

References 0 publications

Linear and nonlinear stratified spindown over sloping topography

Linear and nonlinear stratified spindown over sloping topography

Convective and shear-induced turbulence in the deep Kane Gap

Logarithmic velocity structure in the deep hypolimnetic waters of Lake Michigan

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