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  • 1
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    The Bottom Boundary Layer (2018)
    Annual Reviews
    In:  Annual Review of Marine Science, 10 (1). pp. 397-420.
    Details
    Publication Date: 2020-06-09
    Description: The oceanic bottom boundary layer extracts energy and momentum from the overlying flow, mediates the fate of near-bottom substances, and generates bedforms that retard the flow and affect benthic processes. The bottom boundary layer is forced by winds, waves, tides, and buoyancy and is influenced by surface waves, internal waves, and stratification by heat, salt, and suspended sediments. This review focuses on the coastal ocean. The main points are that (a) classical turbulence concepts and modern turbulence parameterizations provide accurate representations of the structure and turbulent fluxes under conditions in which the underlying assumptions hold, (b) modern sensors and analyses enable high-quality direct or near-direct measurements of the turbulent fluxes and dissipation rates, and (c) the remaining challenges include the interaction of waves and currents with the erodible seabed, the impact of layer-scale two- and three-dimensional instabilities, and the role of the bottom boundary layer in shelf-slope exchange.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1146/annurev-marine-121916-063351
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Observations of near-bottom flow in a wave-dominated nearshore environment (2006)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: To provide observational data for analysis of near-bottom, wave-induced flows, a downward-looking laser Doppler velocimeter (LDV) was deployed to profile the near-bed velocity structure of a six meter water column at a site just outside the surfzone off the coast of North Carolina. 90 second "snap-shots" of the velocity at six elevations below 20 cm above bottom were measured at 25 Hz, while pressure was concurrently measured at 126 cm above bottom. The near-bottom data were supplemented with a benthic acoustic stress sensor (BASS) at approximately 20 cm above bottom which concurrently measured velocity components at 10 Hz. The purposes of this report are to document the collection, processing and archival of these data and to present the profiles for evaluation.
    Description: Funding was provided by the Coastal Sciences Program of the Office of Naval Research under Grant N00014-92-J-12300.
    Keywords: Near-bed velocity ; Wave-induced flow ; Bass/LDV measurements ; Larc (Ship) Cruise
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: 5748092 bytes
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  • 3
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    Significance of Langmuir circulation in upper ocean mixing : comparison of observations and simulations (2010)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L10603, doi:10.1029/2009GL037620.
    Description: Representing upper ocean turbulence accurately in models remains a great challenge for improving weather and climate projections. Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum, heat, and mass in the oceanic surface layer. We present a direct comparison between observations and large eddy simulations, based on the wave-averaged Navier-Stokes equation, of an LC growth event. The evolution of cross-wind velocity variance and spatial scales, as well as mixed layer deepening are only consistent with simulations if LC effects are included in the model. Our results offer a validation of the large eddy simulation approach to understanding LC dynamics, and demonstrate the importance of LC in ocean surface layer mixing.
    Description: This research was supported by the Office of Naval Research through grants N00014-09-M-0112 (TK) and N00014-06-1-0178 (AP, JT). TK also received support from a Woods Hole Oceanographic Institution Cooperative Institute for Climate and Ocean Research Postdoctoral Scholarship.
    Keywords: Langmuir circulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    The influence of crosswind tidal currents on Langmuir circulation in a shallow ocean (2011)
    American Geophysical Union
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C08005, doi:10.1029/2011JC006971.
    Description: Langmuir circulation (LC) is a turbulent process driven by wind and surface waves that plays a key role in transferring momentum, heat, and mass in the oceanic surface layer. On the coastal shelves the largest-scale LC span the whole water column and thus couple the surface and bottom boundary layers and enhance turbulent mixing. Observations and large eddy simulations (LES) of a shallow coastal ocean demonstrate that these relatively large scale Langmuir cells are strongly influenced by crosswind tidal currents. Two mechanisms by which crosswind tidal shear may distort and disrupt Langmuir cells are proposed. The first mechanism involves cell shearing due to differential advection across the whole cell. For the second mechanism, middepth vertical LC currents advect sheared mean crosswind current, leading to the attraction of upwelling and downwelling regions, so that LC cells are unsustainable when both regions overlap. Scaling arguments indicate that LC cells are more susceptible to crosswind shear distortion for smaller LC surface velocity convergence and greater cell aspect ratio (vertical to horizontal LC scale), which is consistent with the results obtained from the observations and LES. These results imply that scaling of LC characteristics in a coastal ocean differs from that in the open ocean, which has important practical implications for parameterizing enhanced mixing due to LC.
    Description: This research was supported by the Office of Naval Research through grant N00014‐06‐1‐0178 (A.P., J.T.). Author T.K. received support from Faculty Startup Funds of the University of Delaware College of Earth, Ocean, and Environment.
    Keywords: Langmuir circulation ; Boundary layer dynamics ; Tides
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 5
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    Mechanisms of surface wave energy dissipation over a high-concentration sediment suspension (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 1638–1681, doi:10.1002/2014JC010245.
    Description: Field observations from the spring of 2008 on the Louisiana shelf were used to elucidate the mechanisms of wave energy dissipation over a muddy seafloor. After a period of high discharge from the Atchafalaya River, acoustic measurements showed the presence of 20 cm thick mobile fluid-mud layers during and after wave events. While total wave energy dissipation (D) was greatest during the high energy periods, these periods had relatively low normalized attenuation rates (κ = Dissipation/Energy Flux). During declining wave-energy conditions, as the fluid-mud layer settled, the attenuation process became more efficient with high κ and low D. The transition from high D and low κ to high κ and low D was caused by a transition from turbulent to laminar flow in the fluid-mud layer as measured by a Pulse-coherent Doppler profiler. Measurements of the oscillatory boundary layer velocity profile in the fluid-mud layer during laminar flow reveal a very thick wave boundary layer with curvature filling the entire fluid-mud layer, suggesting a kinematic viscosity 2–3 orders of magnitude greater than that of clear water. This high viscosity is also consistent with a high wave-attenuation rates measured by across-shelf energy flux differences. The transition to turbulence was forced by instabilities on the lutocline, with wavelengths consistent with the dispersion relation for this two-layer system. The measurements also provide new insight into the dynamics of wave-supported turbidity flows during the transition from a laminar to turbulent fluid-mud layer.
    Description: This work was supported by Office of Naval Research Award N00014-06-1–0718, which was part of the ONR Multidisciplinary University Research Initiative (MUD-MURI): entitled ‘‘Mechanisms of Fluid-Mud Interactions Under Waves.’’ Additional support was provided by National Science Foundation grant 1059914.
    Description: 2015-09-19
    Keywords: Fluid mud ; Wave dissipation ; Laminar and turbulent wave boundary layers ; Lutocline instabilities ; Wave-supported turbidity flows
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
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    Observations of turbulence in the ocean surface boundary layer : energetics and transport (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 39 (2009): 1077–1096, doi:10.1175/2008JPO4044.1.
    Description: Observations of turbulent kinetic energy (TKE) dynamics in the ocean surface boundary layer are presented here and compared with results from previous observational, numerical, and analytic studies. As in previous studies, the dissipation rate of TKE is found to be higher in the wavy ocean surface boundary layer than it would be in a flow past a rigid boundary with similar stress and buoyancy forcing. Estimates of the terms in the turbulent kinetic energy equation indicate that, unlike in a flow past a rigid boundary, the dissipation rates cannot be balanced by local production terms, suggesting that the transport of TKE is important in the ocean surface boundary layer. A simple analytic model containing parameterizations of production, dissipation, and transport reproduces key features of the vertical profile of TKE, including enhancement near the surface. The effective turbulent diffusion coefficient for heat is larger than would be expected in a rigid-boundary boundary layer. This diffusion coefficient is predicted reasonably well by a model that contains the effects of shear production, buoyancy forcing, and transport of TKE (thought to be related to wave breaking). Neglect of buoyancy forcing or wave breaking in the parameterization results in poor predictions of turbulent diffusivity. Langmuir turbulence was detected concurrently with a fraction of the turbulence quantities reported here, but these times did not stand out as having significant differences from observations when Langmuir turbulence was not detected.
    Description: The Office of Naval Research funded this work as a part of CBLAST-Low.
    Keywords: Turbulence ; Boundary layer ; Sea/ocean surface ; Air-sea interaction ; Energy transport
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 7
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    Vertical structure of dissipation in the nearshore (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2007. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 37 (2007): 1764-1777, doi:10.1175/jpo3098.1.
    Description: The vertical structure of the dissipation of turbulence kinetic energy was observed in the nearshore region (3.2-m mean water depth) with a tripod of three acoustic Doppler current meters off a sandy ocean beach. Surface and bottom boundary layer dissipation scaling concepts overlap in this region. No depth-limited wave breaking occurred at the tripod, but wind-induced whitecapping wave breaking did occur. Dissipation is maximum near the surface and minimum at middepth, with a secondary maximum near the bed. The observed dissipation does not follow a surfzone scaling, nor does it follow a “log layer” surface or bottom boundary layer scaling. At the upper two current meters, dissipation follows a modified deep-water breaking-wave scaling. Vertical shear in the mean currents is negligible and shear production magnitude is much less than dissipation, implying that the vertical diffusion of turbulence is important. The increased near-bed secondary dissipation maximum results from a decrease in the turbulent length scale.
    Description: Funding was provided by NSF and ONR.
    Keywords: Turbulence ; Kinetic energy ; Ocean
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 8
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    The effect of wave breaking on surf-zone turbulence and alongshore currents : a modeling study (2010)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 2187–2203, doi:10.1175/JPO2800.1.
    Description: The effect of breaking-wave-generated turbulence on the mean circulation, turbulence, and bottom stress in the surf zone is poorly understood. A one-dimensional vertical coupled turbulence (k–ε) and mean-flow model is developed that incorporates the effect of wave breaking with a time-dependent surface turbulence flux and uses existing (published) model closures. No model parameters are tuned to optimize model–data agreement. The model qualitatively reproduces the mean dissipation and production during the most energetic breaking-wave conditions in 4.5-m water depth off of a sandy beach and slightly underpredicts the mean alongshore current. By modeling a cross-shore transect case example from the Duck94 field experiment, the observed surf-zone dissipation depth scaling and the observed mean alongshore current (although slightly underpredicted) are generally reproduced. Wave breaking significantly reduces the modeled vertical shear, suggesting that surf-zone bottom stress cannot be estimated by fitting a logarithmic current profile to alongshore current observations. Model-inferred drag coefficients follow parameterizations (Manning–Strickler) that depend on the bed roughness and inversely on the water depth, although the inverse depth dependence is likely a proxy for some other effect such as wave breaking. Variations in the bed roughness and the percentage of breaking-wave energy entering the water column have a comparable effect on the mean alongshore current and drag coefficient. However, covarying the wave height, forcing, and dissipation and bed roughness separately results in an alongshore current (drag coefficient) only weakly (strongly) dependent on the bed roughness because of the competing effects of increased turbulence, wave forcing, and orbital wave velocities.
    Description: This work was funded by NSF, ONR, and NOPP.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
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    Turbulence in the coastal environment during HYCODE (2005)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: A tall tripod equipped with two acoustic Doppler velocimeters (ADVs) was deployed at a water depth of 15 m off the coast of New Jersey near the LEO-15 site. Sensors were co-located near the bottom to provide good estimates of Reynolds stress. Thermistors were located within several centimeters of the velocity sample volume to provide simultaneously sampled estimates of turbulent temperature variance and vertical temperature flux. One of the ADVs was equipped with a pressure and a temperature sensor. A wave/tide gauge was placed at 4 meters above bottom. The instruments were deployed late July through early December of 2000 and late June through early August of 2001. For the 2001 deployment, a single beam acoustic Doppler velocity sensor (DopBeam) was added to measure high frequency vertical velocity variance and echo intensity within the bottom boundary layer. A second tripod was deployed nearby and was equipped with an array of LISST sensors and an MSCAT. The purpose of this report is to document the instrumentation and deployment of the tripods and to document the tall tripod data by providing a description of the processing and data formats, time-series summaries of the burst averaged data along with preliminary analyses.
    Description: Funding was provided by the Office of Naval Research under Contract No. N00014-99-1-0213.
    Keywords: Turbulence ; Stress ; HYCODE ; Endeavor (Ship: 1976-) Cruise EN342 ; Endeavor (Ship: 1976-) Cruise EN344 ; Endeavor (Ship: 1976-) Cruise EN347 ; Endeavor (Ship: 1976-) Cruise EN356 ; Endeavor (Ship: 1976-) Cruise EN358
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: 3582726 bytes
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  • 10
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    Stress, salt flux, and dynamics of a partially mixed estuary (2005)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: A field study was performed in the lower Hudson River, a partially mixed estuary with a relatively simple geometry (Figure 1), between August and October of 1995. The objectives of the study were (1) to quantify and characterize the turbulent transport of momentum and salt, and (2) to relate the turbulent transport processes to the local and estuary-wide dynamics. The measurement program consisted of fixed and shipboard components. At a central site, a moored array of temperature-conductivity sensors and optical backscatter sensors (OBS), a bottom-mounted acoustic Doppler current profiler (ADCP), and a bottom-mounted array of acoustic travel-time current sensors (BASS), temperature-conductivity sensors, and OBS sensors resolved the vertical structure of velocity, salinity and turbidity and the near-bottom turbulence structure. Moored and bottom-mounted velocity, temperature, conductivity and pressure sensors at five secondary sites quantified the spatial and temporal variabilty of velocity, salinity and bottom pressure. Shipboard measurements with an ADCP and a conductivity-temperature-depth (CTD) profiler, accompanied by an OBS sensor, resolved the spatial structure and tidal variability of velocity, salinity and turbidity along several cross-channel and along-channel transects. This report describes the measurements in detail. Section II describes the instrumentation, Section III describes the deployment and sampling schemes, Section IV describes the data processing, and Section V is a summary of plots of selected data. Section VI documents the data files and Sections VII and VII give acknowledgments and references.
    Description: Funding was provided by the National Science Foundation under Grant OCE-94-15617 and The Hudson River Foundation.
    Keywords: Stress ; Salt flux ; Mixed estuary
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: 9092431 bytes
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