Stratification Prediction and Bottom Boundary Layer Dynamics Over the Texas-Louisiana Continental Shelf PDF Download
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Author: Wenxia Zhang
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Languages : en
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The bottom boundary layer is an unstratified thin layer above the sea floor, separated from the more strongly stratified interior. Formation of a thin bottom boundary layer in the presence of stratification and a sloping bottom is common, and well characterized by theory. This thin layer is an important source of mixing over the continental shelf, and it plays a fundamental role in several continental shelf physical and biogeochemical processes, such as buoyancy advection, bottom material transport and hypoxia formation. In this research, Both observations and numerical models are used to study models' ability of reproducing observed stratification and bottom boundary layer dynamics over the Texas-Louisiana shelf. Simulated vertical stratification, which is also representing the vertical density structure, was first evaluated since it directly controls the bottom boundary layer structure itself and is important for other bottom boundary layer dynamics. A new metric, the histogram of vertical stratification, is introduced in this research to evaluate the models' ability of reproducing observed stratification in a bulk sense. The improvement in model performance is attributed to the finer horizontal and temporal resolutions of a model, while factors like open boundary conditions and vertical resolutions are modified without any improvement in the ability of the model to simulate observed stratification. Towed, undulating CTD profiles collected during Mechanisms Controlling Hypoxia (MCH) program also detected mid-water oxygen minima in many transects. These intrusions are connected with the bottom boundary layer and follows the pycnocline seaward as a mid-water column tongue of low oxygen. We calculate convergence within the bottom boundary layer relative to density surfaces using the simulated results; there is a convergence in the bottom boundary layer at the location where the pycnocline intercepts the bottom, creating an injection of bottom boundary layer water into the pycnocline. Convergent flow at the bottom, relative to isopycnal surfaces, is strongest in the density classes associated with the oxygen minimum layer. We believe these mid-water oxygen minima are actually intrusions of low oxygen protruding from the bottom boundary layer via buoyancy advection driven convergence, following the main pycnocline. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155027
Author: Wenxia Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The bottom boundary layer is an unstratified thin layer above the sea floor, separated from the more strongly stratified interior. Formation of a thin bottom boundary layer in the presence of stratification and a sloping bottom is common, and well characterized by theory. This thin layer is an important source of mixing over the continental shelf, and it plays a fundamental role in several continental shelf physical and biogeochemical processes, such as buoyancy advection, bottom material transport and hypoxia formation. In this research, Both observations and numerical models are used to study models' ability of reproducing observed stratification and bottom boundary layer dynamics over the Texas-Louisiana shelf. Simulated vertical stratification, which is also representing the vertical density structure, was first evaluated since it directly controls the bottom boundary layer structure itself and is important for other bottom boundary layer dynamics. A new metric, the histogram of vertical stratification, is introduced in this research to evaluate the models' ability of reproducing observed stratification in a bulk sense. The improvement in model performance is attributed to the finer horizontal and temporal resolutions of a model, while factors like open boundary conditions and vertical resolutions are modified without any improvement in the ability of the model to simulate observed stratification. Towed, undulating CTD profiles collected during Mechanisms Controlling Hypoxia (MCH) program also detected mid-water oxygen minima in many transects. These intrusions are connected with the bottom boundary layer and follows the pycnocline seaward as a mid-water column tongue of low oxygen. We calculate convergence within the bottom boundary layer relative to density surfaces using the simulated results; there is a convergence in the bottom boundary layer at the location where the pycnocline intercepts the bottom, creating an injection of bottom boundary layer water into the pycnocline. Convergent flow at the bottom, relative to isopycnal surfaces, is strongest in the density classes associated with the oxygen minimum layer. We believe these mid-water oxygen minima are actually intrusions of low oxygen protruding from the bottom boundary layer via buoyancy advection driven convergence, following the main pycnocline. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/155027
Author: Zheng Zhang
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Languages : en
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Turbulent dynamics at two sites (C and D) in a hypoxic zone on the Texas- Louisiana continental shelf were studied by investigating turbulence quantities i.e. turbulence kinetic energy (TKE), dissipation rate of TKE (E), Reynolds stress (T), dissipation rate of temperature variance (X), eddy diffusivity of temperature (v't), and eddy diffusivity of density (v'p). Numerical models were also applied to test their capability of simulating these turbulence quantities. At site D, TKE, E, and T were calculated from velocity measurements in the bot- tom boundary layer (BBL), using the Kolmogorov's -5/3 law in the inertial subrange of energy spectra of vertical velocity fluctuations in each burst measurement. Four second-moment turbulence closure models were applied for turbulence simulations, and modeled turbulence quantities were found to be consistent with those observed. It was found from inter-model comparisons that models with the stability functions of Schumann and Gerz predicted higher values of turbulence quantities than those of Cheng in the mid layer, which might be due to that the former stability functions are not sensitive to buoyancy. At site C, X, E, v't, and v'p were calculated from profile measurements throughout the water column, and showed high turbulence level in the surface boundary layer and BBL, as well as in the mid layer where shear stress was induced by advected non-local water above a hypoxic layer. The relatively high dissolved oxygen in the non-local water resulted in upward and downward turbulent oxygen fluxes, and the bottom hypoxia will deform due to turbulence in 7.11 days. Two of the four models in the study at site D were implemented, and results showed that turbulence energy resulting from the non-local water was not well reproduced. We attribute this to the lack of high-resolution velocity measurements for simulations. Model results agreed with observations only for X and E simulated from the model with the stability function of Cheng in the BBL. Discrepancies between model and observational results lead to the following conclusions: 1) the stability functions of Schumann and Gerz are too simple to represent the turbulent dynamics in stratified mid layers; 2) detailed velocity profiles measurements are required for models to accurately predict turbulence quantities. Missing such observations would result in underestimation. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151031
Author: William J. Shaw
Publisher:
ISBN:
Category : Continental shelf
Languages : en
Pages : 376
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The bottom boundary layer is an important dynamical region of shallow water flows. In this thesis, the problem of turbulent mixing in the coastal bottom boundary layer is investigated with a unique set of field measurements of velocity and sound speed that span a significant fraction of the boundary layer obtained over a six-week long period in the late summer of 1996 on the New England shelf. The energetics of the turbulent fluctuations are investigated by testing simplified budgets for turbulent kinetic energy and scalar variance. The turbulent kinetic energy budget is locally balanced while the scalar variance budget is not, probably due to turbulent diffusion. The direct effects of stratification are consistently significant only in the outer part of the boundary layer, where the flux Richardson number is approximately equal to a critical value of 0.2. Turbulence closure is investigated in terms of non-dimensional profiles of velocity and sound speed. Close to the bottom, the results are consistent with Monin-Obukhov similarity theory, while in the outer part of the boundary layer other scales including the height of the boundary layer are important for setting the turbulent length scale.
Author: Scott Michael Glenn
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 246
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Author:
Publisher: Academic Press
ISBN: 0080878857
Category : Science
Languages : en
Pages : 4604
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The study of estuaries and coasts has seen enormous growth in recent years, since changes in these areas have a large effect on the food chain, as well as on the physics and chemistry of the ocean. As the coasts and river banks around the world become more densely populated, the pressure on these ecosystems intensifies, putting a new focus on environmental, socio-economic and policy issues. Written by a team of international expert scientists, under the guidance of Chief Editors Eric Wolanski and Donald McClusky, the Treatise on Estuarine and Coastal Science, Ten Volume Set examines topics in depth, and aims to provide a comprehensive scientific resource for all professionals and students in the area of estuarine and coastal science Most up-to-date reference for system-based coastal and estuarine science and management, from the inland watershed to the ocean shelf Chief editors have assembled a world-class team of volume editors and contributing authors Approach focuses on the physical, biological, chemistry, ecosystem, human, ecological and economics processes, to show how to best use multidisciplinary science to ensure earth's sustainability Provides a comprehensive scientific resource for all professionals and students in the area of estuarine and coastal science Features up-to-date chapters covering a full range of topics
Author: Richard Brent Styles
Publisher:
ISBN:
Category :
Languages : en
Pages : 522
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Author: William D. Grant
Publisher:
ISBN:
Category : Boundary layer
Languages : en
Pages : 163
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Author:
Publisher:
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Category : Petrology
Languages : en
Pages :
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Author: Barry M. Lesht
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ISBN:
Category : Continental shelf
Languages : en
Pages : 502
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Author: Society of Economic Paleontologists and Mineralogists. Gulf Coast Section. Foundation. Research Conference
Publisher:
ISBN:
Category : Continental shelf
Languages : en
Pages : 224
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