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  • 11
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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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  • 12
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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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  • 13
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    On the exchange of momentum over the open ocean (2013)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2013. 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 43 (2013): 1589–1610, doi:10.1175/JPO-D-12-0173.1.
    Description: This study investigates the exchange of momentum between the atmosphere and ocean using data collected from four oceanic field experiments. Direct covariance estimates of momentum fluxes were collected in all four experiments and wind profiles were collected during three of them. The objective of the investigation is to improve parameterizations of the surface roughness and drag coefficient used to estimate the surface stress from bulk formulas. Specifically, the Coupled Ocean–Atmosphere Response Experiment (COARE) 3.0 bulk flux algorithm is refined to create COARE 3.5. Oversea measurements of dimensionless shear are used to investigate the stability function under stable and convective conditions. The behavior of surface roughness is then investigated over a wider range of wind speeds (up to 25 m s−1) and wave conditions than have been available from previous oversea field studies. The wind speed dependence of the Charnock coefficient α in the COARE algorithm is modified to , where m = 0.017 m−1 s and b = −0.005. When combined with a parameterization for smooth flow, this formulation gives better agreement with the stress estimates from all of the field programs at all winds speeds with significant improvement for wind speeds over 13 m s−1. Wave age– and wave slope–dependent parameterizations of the surface roughness are also investigated, but the COARE 3.5 wind speed–dependent formulation matches the observations well without any wave information. The available data provide a simple reason for why wind speed–, wave age–, and wave slope–dependent formulations give similar results—the inverse wave age varies nearly linearly with wind speed in long-fetch conditions for wind speeds up to 25 m s−1.
    Description: This work was funded by the National Science Foundation Grant OCE04-24536 as part of the CLIVAR Mode Water Dynamics Experiment (CLIMODE) and the Office of Naval Research Grant N00014-05-1-0139 as part of the CBLAST-LOW program.
    Description: 2014-02-01
    Keywords: Wind shear ; Wind stress ; Atmosphere-ocean interaction ; Fluxes ; Momentum ; Algorithms
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 14
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    Inhibited upper ocean restratification in nonequilibrium swell conditions (2013)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. 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 40 (2013): 3672–3676, doi:10.1002/grl.50708.
    Description: Diurnal restratification of the ocean surface boundary layer (OSBL) represents a competition between mixing of the OSBL and solar heating. Langmuir turbulence (LT) is a mixing process in the OSBL, driven by wind and surface waves, that transfers momentum, heat, and mass. Observations in nonequilibrium swell conditions reveal that the OSBL does not restratify despite low winds and strong solar radiation. Motivated by observations, we use large-eddy simulations of the wave-averaged Navier-Stokes equations to show that LT is capable of inhibiting diurnal restratification of the OSBL. Incoming heat is redistributed vertically by LT, forming a warmer OSBL with a nearly uniform temperature. The inhibition of restratification is not reproduced by two common Reynolds-averaged Navier-Stokes equation models, highlighting the importance of properly representing sea-state dependent LT dynamics in OSBL models.
    Description: This work was supported by the U.S. National Science Foundation (Grant OCE-1130678).
    Description: 2014-01-30
    Keywords: Swell ; Upper ocean turbulence ; Restratification ; Diurinal heating ; Langmuir turbulence ; Langmuir circulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 15
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    The Ocean Observatories Initiative (2018)
    The Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2018. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 31, no. 1 (2018): 16–35, doi:10.5670/oceanog.2018.105.
    Description: The Ocean Observatories Initiative (OOI) is an integrated suite of instrumented platforms and discrete instruments that measure physical, chemical, geological, and biological properties from the seafloor to the sea surface. The OOI provides data to address large-scale scientific challenges such as coastal ocean dynamics, climate and ecosystem health, the global carbon cycle, and linkages among seafloor volcanism and life. The OOI Cyberinfrastructure currently serves over 250 terabytes of data from the arrays. These data are freely available to users worldwide, changing the way scientists and the broader community interact with the ocean, and permitting ocean research and inquiry at scales of centimeters to kilometers and seconds to decades.
    Description: Funding for the OOI is provided by the National Science Foundation through a Cooperative Support Agreement with the Consortium for Ocean Leadership (OCE-1026342).
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 16
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    Atmospheric and offshore forcing of temperature variability at the shelf break (2018)
    The Oceanography Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Oceanography Society, 2018. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 31, no. 1 (2018): 72–79, doi:10.5670/oceanog.2018.112.
    Description: Knowledge of heat balance and associated temperature variability in the Northwest Atlantic coastal ocean is important for understanding impacts of climate change such as how ocean warming will affect the management of fisheries. Heat balances are particularly complicated near the edge of the continental shelf, where the cross-shelf temperature gradients within the shelf-break front complicate the competing influences of air-sea flux anomalies versus ocean advection. We review the atmospheric and oceanic processes associated with heat balance over the Northwest Atlantic continental shelf and slope, with an emphasis on the scale-dependent nature of the heat balance. We then use data from the Ocean Observatories Initiative (OOI) Pioneer Array to demonstrate heat balance scale dependence at the southern New England shelf break, and the capability of the array to capture multiscale ocean processes. Comparison of the cumulative effects of air-sea heat fluxes measured at the OOI Pioneer Array from May 2015 to April 2016 with the actual temperature change shows the importance of advective processes in overall heat balance near the shelf break.
    Description: KC was partially supported by the National Science Foundation under grant OCE-1435602 and OCE- 1634094. GG was supported by the National Science Foundation under grant OCE-1657853. AP was supported by the National Science Foundation through the Cooperative Agreement (subaward) SA9-10 from the Consortium for Ocean Leadership to the Woods Hole Oceanographic Institution.
    Repository Name: Woods Hole Open Access Server
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  • 17
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    Upper ocean momentum balances in the western equatorial Pacific on the intraseasonal time scale (2006)
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © The Authors, 2004. This is the author's version of the work. It is posted here by permission of Elsevier B. V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 52 (2005): 749-765, doi:10.1016/j.dsr.2004.12.004.
    Description: Surface Meteorology, upper ocean current, and hydrographic measurements, collected along a repeated survey pattern and from a central mooring in the western equatorial Pacific during late 1992 to early 1993, were used to analyse upper ocean momentum balances on the intraseasonal time scale. Wind stresses derived from meteorological measurements were compared with numerical weather prediction products. Advection terms in the momentum equations were estimated by planar fits to the current and hydrographic data. Pressure gradient terms were derived from planar fits to the dynamic heights calculated from the hydrographic data, referenced by balancing the momentum equation in a selected layer below the mixed layer. Under prevailing westerly winds, westward pressure gradient forcings of 2x10-7 m s-2 were set up in the western equatorial Pacific, countering the surface wind, while the total advection tended to accelerate the eastward momentum in the surface layer. During both calm wind and westerly wind burst periods, zonal turbulent momentum fluxes estimated from the ocean budgets were comparable with those estimated from microstructure dissipation rate measurements and with zonal wind stresses, so that the zonal momentum could be balanced within error bars. The meridional momentum balances were noisier, which might be due to the fact that the short meridional length scale of the equatorial inertial-gravity waves could contaminate the dynamic signals in the mixed temporal/spatial sampling data, so that the meridional gradient estimates from the planar fits could be biased.
    Description: MF acknowledges the support of Strategic Research Fund for Marine Environment. RL and PH were supported by NSF grant OCE-9525986. RW and AP were supported by NSF Grants OCE- 9110559 and OCE-9110554, respectively.
    Repository Name: Woods Hole Open Access Server
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  • 18
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    Design study for a moored surface-scanning sonar (2006)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: This report contains the results of a design study for a surface scanning sonar instrument capable of long-term deployment on ocean moorings. The instrument is intended to sample the bubble field just below the ocean's surface and compute the backscattered intensity and Doppler velocity in small unit volumes. The principal motivation for the development of such an instrument is to enhance the study of upper ocean processes by utilizing the ability of the sonar to detect surface waves and Langmuir circulation. Important design parameters for the instrument are investigated and a detailed design proposed. Key technical issues such as the trade-offs among spatial resolution, temporal resolution, velocity precision, total range, and power are discussed. The azimuthal motion of the instrument on a mooring is considered as a potential problem, and possible solutions are discussed. Matlab functions used for the investigations are included in an appendix.
    Description: Funding was provided by a grant from the Webster Foundation to the Woods Hole Oceanographic Institution.
    Keywords: Doppler sonar ; Surface scanning ; Moored instrumentation
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
    Format: 1967415 bytes
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  • 19
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    Corrigendum (2010)
    American Meteorological Society
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    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2010. 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 40 (2010): 1910–1914, doi:10.1175/2010JPO4483.1.
    Description: Corrigendum: Spall, M. A., R. S. Pickart, P. S. Fratantoni, and A. J. Plueddemann, 2008: Western Arctic shelfbreak eddies: Formation and transport. J. Phys. Oceanogr., 38, 1644–1668
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 20
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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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