Дисертації з теми "Oceanic mixing"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Oceanic mixing.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Oceanic mixing".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Brainerd, Keith. "Upper ocean turbulence, mixing, and stratification /." Thesis, Connect to this title online; UW restricted, 1995. http://hdl.handle.net/1773/11007.
2
Kay, David J. "Mixing processes in a highly stratified tidal flow /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/9639.
3
Carter, Glenn S. "Turbulent mixing near rough topography /." Thesis, Connect to this title online; UW restricted, 2005. http://hdl.handle.net/1773/10976.
4
Font, i. Ferré Jordi. "La circulació general a la mar Catalana." Barcelona : Centre de Publicacions, Intercanvi Cientific i Extensio Universitaria, Universitat de Barcelona, 1986. http://catalog.hathitrust.org/api/volumes/oclc/32908084.html.
5
Wells, Mathew Graeme. "Convection, turbulent mixing and salt fingers." View thesis entry in Australian Digital Theses Program, 2001. http://thesis.anu.edu.au/public/adt-ANU20011212.103012/index.html.
6
Xu, Danya. "Lagrangian Study of Particle Transport Processes in the Coastal Gulf of Maine." Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/XuD2008.pdf.
7
Straneo, Fiammetta. "Dynamics of rotating convection including a horizontal stratification and wind /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/10996.
8
Deese, Heather E. "Chaotic advection and mixing in a western boundary current-recirculation system : laboratory experiments /." Online version, 2000. http://hdl.handle.net/1912/3036.
Анотація:
Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), February 2001.Includes bibliographical references (p. 116-118).
9
Chadwick, David Bartholomew. "Tidal exchange at the bay-ocean boundary /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823709.
10
Hamme, Roberta Claire. "Applications of neon, nitrogen, argon, and oxygen to physical, chemical, and biological cycles in the ocean /." Thesis, Connect to this title online; UW restricted, 2003. http://hdl.handle.net/1773/10997.
11
McCabe, Ryan Matthew. "Small-scale coastal dynamics and mixing from a Lagrangian perspective /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/10963.
12
McPhee, Erika E. "Internal-wave mixing along sloping boundaries : a mechanism for generating intermediate nepheloid layers /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/10972.
13
Páramo, Pedro. "Seismic studies of continental rupture and ocean finestructure in the Gulf of California." Laramie, Wyo. : University of Wyoming, 2006. http://proquest.umi.com/pqdweb?did=1144186761&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
14
Hartnett, Hilairy Ellen. "Organic carbon input, degradation, and preservation in continental margin sediments : an assessment of the role of a strong oxygen deficient zone /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/10961.
15
Dunne, John P. "Measured and modeled particle export in equatorial and coastal upwelling regions /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/11043.
16
Rice, Ana E. "Mixing dynamics in the Delaware Bay and adjacent shelf." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 156 p, 2009. http://proquest.umi.com/pqdweb?did=1833621161&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
17
Galí, Tàpias Martí. "Interactive effects of vertical mixing, solar radiation and microbial activity on oceanic dimethylated sulfur cycling." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/117383.
Анотація:
The production and subsequent emission of volatile compounds is one of the numerous ways by which microbial plankton participate in the cycling of elements and influence the Earth's climate. Dimethylsulfide (DMS), produced by enzymatic decomposition of the algal intracellular compound dimethylsulfoniopropionate (DMSP), is the more abundant organic volatile in the upper ocean. Its global emission amounts ca. 28 Tg S per year, and represents the main biogenic source of sulfur to the troposphere and about 30% of the total S emission (anthropogenic, biogenic and volcanic). Atmospheric oxidation of DMS contributes to atmospheric acidity, and is believed to promote the formation and growth of aerosols. Furthermore, DMSderived sulfate aerosols have been suggested to cool the climate by reducing the amount of shortwave solar radiation reaching the Earth's
surface through two mechanisms: by scattering solar radiation and, more important, by acting as cloud condensation nuclei, thus making clouds brighter and longerlived.
The `CLAW' hypothesis postulates that, if oceanic DMS emission was in turn stimulated by solar radiation, a regulatory feedback mechanism could operate between marine plankton and the radiative budget over the oceans. However, the relationship between DMS emission and solar radiation is not straightforward, since a number of biochemical and photochemical transformations come into action from the moment DMSP is synthesized by phytoplankton until DMS is emitted. These transformations are intimately linked to the physical environment, the ecological setting and the microbial interactions, rendering the picture of dimethylated sulfur cycling a lot more complicated. Surprisingly, though, the seasonal cycle of seawater
DMS concentration seems to follow that of solar radiation in the majority of oceanic regions, regardless their productivity regimes.
The premise of this thesis is that, to understand this emerging pattern, we need to understand what regulates the DMS production and consumption processes and their balance (that is, DMS budgets). To this end, we have studied the response of biotic and abiotic DMS cycling to solar radiation by means of incubation experiments. At another level, we have studied the response of ecosystem DMS budgets to different radiation climates. Since the depth of the upper mixed layer regulates the amount and spectral composition of the `light' seen by the cells and molecules, our studies have been backed by a careful characterization of underwater radiation fields and vertical mixing dynamics.
Our results show that solar radiation has a stimulating effect on gross DMS production. Moreover, the stimulation is more effective at shorter and more energetic wavelengths in the ultraviolet (UV) region. Direct DMS production and/or increased DMSP release by UVstressed phytoplankton is the most plausible explanation for this observation, leaving a secondary role for DMS production mechanisms related to bacterial metabolism and microzooplankton grazing. At the ecosystem level, we have shown that vertical mixingmediated solar exposure regulates whether DMS is preferentially oxidized by bacteria or by photochemical reactions. The outcome of this competition between DMS sinks is that total DMS loss rate constants vary little across oceanic biomes. As a result, the seasonal and also the shortterm variability in DMS concentrations respond mainly to gross DMS production. The stress
response occurs at different temporal scales: seasonally, through the succession of microbial communities towards stronger DMSP producers and higher DMS yields in summer stratified waters; and across daynight cycles, where shortterm radiative stress modulates DMSP to DMS conversion yields. By means of a literature metaanalysis, we have improved the current understanding of the different DMS(P) cycling regimes and their links with the ecological geography of the sea.
18
Pollmann, Friederike [Verfasser], and Carsten [Akademischer Betreuer] Eden. "Oceanic internal gravity waves and turbulent mixing : observations and parameterizations / Friederike Pollmann ; Betreuer: Carsten Eden." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2018. http://d-nb.info/1151322423/34.
19
Martin, Michiko J. "An investigation of momentum exchange parameterizations and atmospheric forcing for the Coastal Mixing and Optics Program." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/55324.
Анотація:
Thesis (S.M.)--Joint Program in Applied Ocean Physics and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1998.Includes bibliographic references (p. 77-83).
This thesis presents an investigation of the influence of surface waves on momentum exchange. A quantitative comparison of direct covariance friction velocity measurements to bulk aerodynamic and inertial dissipation estimates indicates that both indirect methods systematically underestimate the momentum flux into developing seas. To account for wave-induced processes and yield improved flux estimates, modifications to the traditional flux parameterizations are explored. Modification to the bulk aerodynamic method involves incorporating sea state dependence into the roughness length calculation. For the inertial dissipation method, a new parameterization for the dimensionless dissipation rate is proposed. The modifications lead to improved momentum flux estimates for both methods.
by Michiko J. Martin.
S.M.
20
Lee, Bing-Sun. "Uses of chlorofluorocarbons as ocean tracers and for estimating the removal rates of CFC-11 and carbon tetrachloride in certain marine environments /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/11048.
21
MacKinnon, Jennifer A. "Coastal recipes : internal waves, turbulence and mixing on the New England continental shelf /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/11063.
22
Alford, Matthew. "Observations of overturning and double diffusive processes in the thermocline : the context of ocean mixing /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1998. http://wwwlib.umi.com/cr/ucsd/fullcit?p9907820.
23
Johnson, Clare. "Tracing Wyville Thomson Ridge overflow water in the Rockall Trough." Thesis, University of the Highlands and Islands, 2012. https://pure.uhi.ac.uk/portal/en/studentthesis/tracing-wyville-thomson-ridge-overflow-water-in-the-rockall-trough(07bd114b-bbec-4efe-9a13-783ba80ff83d).html.
Анотація:
Although it has long been known that cold dense waters from the Nordic Seas overflow the Wyville Thomson Ridge, the water masses' subsequent pathways and fate have been uncertain. This study conclusively places Wyville Thomson Ridge Overflow Water (WTOW) as an important water mass in the eastern subpolar North Atlantic for the first time. Using a variety of chemical tracer s (chlorofluorocarbons, oxygen, nutrients and aluminium) in conjunction with temperature and salinity, WTOW is traced southwards into the northern and central Rockall Trough as well as into the channels between the western banks. The overflow water has a clear temperature, salinity and chlorofluorocarbon (CFC-11 and CFC-12) signature. Additionally, levels of aluminium are elevated in WTOW suggesting that this element is potentially a useful and novel water mass tracer. The lower oxygen layer complicates the use of dissolved oxygen and nitrate as tracers in the mid water column. However, higher and lower concentrations respectively in the western trough reveal the presence of WTOW in this area. The overflow water does not appear to have a silicate or phosphate signature. Two branches of WTOW exist in the Rockall Trough: a slow-moving indistinct intermediate branch (600-1200 m) f ound in both the east and west of the basin; and a coherent deep branch (> 1200 m) that flows southward along the western banks of the trough. As well as having a large spatial footprint within the Rockall Trough, intermediate a nd deep WTOW are temporally persistent being present 65-75 % of the time between 1975 and 2008. The signature of WTOW at intermediate depths is absent from the Ellett Line record in the mid-1980s and early-1990s. As deep WTOW is still observed during these periods flow over the Wyville Thomson Ridge cannot have ceased. Instead, it is proposed that the strength of the Subpolar Gyre is an important driver in the temporal distribution of intermediate WTOW within the Rockall Trough. When the gyre is strong, such as in the mid-1980s and early-1990s, the mid water column is dominated by waters originating from the west which block the southward flow of intermediate WTOW. In contrast, when the gyre is weak, such as in the late-1990s and 2000s, subpolar waters lie further west enabling intermediate waters within the Rockall Trough to be dominated by the southern orig inating Mediterranean Overflow Water and the northern water mass of WTOW.
24
Schanze, Julian J. (Julian Johannes). "The production of temperature and salinity variance and covariance : implications for mixing." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79294.
Анотація:
Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 187-195).
Large-scale thermal forcing and freshwater fluxes play an essential role in setting temperature and salinity in the ocean. A number of recent estimates of the global oceanic freshwater balance as well as the global oceanic surface net heat flux are used to investigate the effects of heat- and freshwater forcing at the ocean surface. Such forcing induces changes in both density and density-compensated temperature and salinity changes ('spice'). The ratio of the relative contributions of haline and thermal forcing in the mixed layer is maintained by large-scale surface fluxes, leading to important consequences for mixing in the ocean interior. In a stratified ocean, mixing processes can be either along lines of constant density (isopycnal) or across those lines (diapycnal). The contribution of these processes to the total mixing rate in the ocean can be estimated from the large-scale forcing by evaluating the production of thermal variance, salinity variance and temperature-salinity covariance. Here, I use new estimates of surface fluxes to evaluate these terms and combine them to generate estimates of the production of density and spice variance under the assumption of a linear equation of state. As a consequence, it is possible to estimate the relative importance of isopycnal and diapycnal mixing in the ocean. While isopycnal and diapycnal processes occur on very different length scales, I find that the surface-driven production of density and spice variance requires an approximate equipartition between isopycnal and diapycnal mixing in the ocean interior. In addition, consideration of the full nonlinear equation of state reveals that surface fluxes require an apparent buoyancy gain (expansion) of the ocean, which allows an estimate of the amount of contraction on mixing due to cabbeling in the ocean interior.
by Julian J. Schanze.
Ph.D.
25
Shaw, William J. (William James) 1971. "Mechanisms of turbulent mixing in the Continental Shelf bottom boundary layer." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/58518.
Анотація:
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2000.Includes bibliographic references.
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.
by William J. Shaw.
Ph.D.
26
Ru, Hua. "A 2 1/2 dimensional thermohaline circulation model with boundary mixing." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/58265.
Анотація:
Thesis (S.M.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), 2000.Includes bibliographical references (leaves 78-82).
A simple quasi-two dimensional dynamical model of Thermohaline circulation (THC) is developed, assuming that the mixing only occurs near western and eastern boundary layers. When the surface density is prescribed, the climatically important quantities, such as the strength of overturning and meridional heat transport, are related to the zonal integral over the vigorously mixing regions and scaled as (KvΔx)2/3. The numerical results suggest that the density difference between eastern and western boundaries play an important role in the meridional overturning. The eastern boundary is characterized by the upwelling on top of downwelling. The western boundary layer is featured by the universal upwelling. The inefficiency of diffusion heat transport accounts for the narrowness of sinking region and shallowness of overturning cell in one-hemisphere. The experiments with other surface boundary conditions are also explored. The circulation patterns obtained are similar under various surface temperature distributions, suggesting these are very robust features of THC. The role of boundary mixing is further explored in global ocean. The 2 1/2 dynamical model is extended to two-hemisphere ocean. Additional dynamics such as Rayleigh friction and abyssal water properties are taken into account. A set of complicated governing equations are derived and numerically solved to obtain steady state solution. The basic circulation features are revealed in our dynamical model. An equtorially asymmetric meridional circulation is observed due to small perturbation at the surface temperature in the high latitude. The density differences between eastern and western boundaries are distinct in both hemispheres. This is achieved during the spin-up process. Although the dynamical model results agree well with OGCM results in one-hemisphere, several important dynamics are lacking and exposed in two-hemisphere experiments. We need to consider horizontal advection terms which will effectively advect positive density anomalies across the equator and form the deep water for the entire system.
by Hua Ru.
S.M.
27
Dell, Rebecca Walsh. "Abyssal mixing from bottom boundary effects in Mid-Atlantic Ridge flank canyons." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59657.
Анотація:
Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010.Includes bibliographical references (p. 54-56).
This paper begins to explore a previously neglected mechanism for abyssal ocean mixing using bottom boundary layer dynamics. Abyssal mixing and the associated upward buoyancy fluxes are necessary to balance the sinking of dense waters at high latitudes and to close the global overturning circulation. Previous studies have concentrated on the hypothesis that the primary mechanism for this mixing is breaking internal waves generated by tidal flows over rough topography. However, intriguing observations, particularly from the Brazil Basin Tracer Release Experiment, suggest that mixing in the flank canyons of the Mid-Atlantic Ridge generated when strong mean flows interact with the many sills and constrictions within the canyons may represent a dynamically important amount of abyssal mixing. The energy pathways and mechanisms of this mixing are much less clear than in the case of breaking internal waves. This study attempts to clarify this by suggesting an analogy with an idealized diffusive boundary layer over a sloping bottom. This boundary layer is characterized by up-slope flows powered by the buoyancy flux in the fluid far from the boundary. Here we explore the energy budget of the boundary layer, and find that the diffusive boundary layer provides flows that are generally consistent with those observed in submarine canyons. In addition, we derive the vertical velocity in the far-field fluid, analogous to an Ekman pumping velocity, that these boundary layers can induce when the bottom slope is not constant. Finally, we present both theoretical and numerical models of exchange flows between the bottom boundary and the far-field flow when the bottom slope is not constant. These exchange flows provide a mechanism by which boundary-driven mixing can affect the overall stratification and buoyancy fluxes of the basin interior.
by Rebecca Walsh Dell.
S.M.
28
Kunz, Thomas J. Diehl Sebastian. "Effects of mixing depth, turbulent diffusion, and nutrient enrichment on enclosed marine plankton communities." Connect to this title online, 2005. http://edoc.ub.uni-muenchen.de/archive/00004539/.
Анотація:
Thesis (Ph. D.)--Ludwig-Maximilians-Universität München, 2005..Title from PDF title page (viewed on May 13, 2006). Includes three articles co-authored with Sebastian Diehl. Vita. Includes bibliographical references.
29
Dell, Rebecca Walsh. "Boundary layer dynamics and deep ocean mixing in Mid-Atlantic Ridge canyons." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79282.
Анотація:
Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 160-163).
Physical oceanographers have known for several decades the total amount of abyssal mixing and upwelling required to balance the deep-water formation, but are still working to understand the mechanisms and locations-how and where it happens. From observational studies, we know that areas of rough topography are important and the hundreds of Grand-Canyon sized canyons that line mid-ocean ridges have particularly energetic mixing. To better understand the mechanisms by which rough topography translates into energetic currents and mixing, I studied diffusive boundary layers over varying topography using theoretical approaches and idealized numerical simulations using the ROMS model. In this dissertation, I show a variety of previously unidentified characteristics of diffusive boundary layers that are likely relevant for understanding the circulation of the abyssal ocean. These boundary layers share many important properties with observed flows in abyssal canyons, like increased kinetic energy near topographic sills and strong currents running from the abyssal plains up the slopes of the mid-ocean ridges toward their crests. They also have a previously unknown capacity to accelerate into overflows for a variety of oceanographically relevant shapes and sizes of topography. This acceleration happens without external forcing, meaning such overflows may be ubiquitous in the deep ocean. These boundary layers also can force exchange of large volumes of fluid between the relatively unstratified boundary layer and the stratified far-field fluid, altering the stratification far from the boundary. We see these effects in boundary layers in two- and three-dimensions, with and without rotation. In conclusion, these boundary layer processes, though previously neglected, may be a source of a dynamically important amount of abyssal upwelling, profoundly affecting predictions of the basin-scale circulation. This type of mechanism cannot be captured by the kind of mixing parameterizations used in current global climate models, based on a bottom roughness. Therefore, there is much work still to do to better understand how these boundary layers behave in more realistic contexts and how we might incorporate that understanding into climate models.
by Rebecca Walsh Dell.
Ph.D.
30
Deese, Heather E. (Heather Elizabeth) 1975. "Chaotic advection and mixing in a western boundary current-recirculation system : laboratory experiments." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/53538.
Анотація:
Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2001.Includes bibliographical references (p. 116-118).
I study the exchange between a boundary current and flanking horizontal recirculations in a 'sliced-cylinder' rotating tank laboratory experiment. Two flow configurations are investigated: a single recirculation and a double, figure-8, recirculation. The latter case involves a hyperbolic point, while the former does not. I investigate the stirring and mixing under both steady and unsteady forcing. I quantify the mixing in each case using effective diffusivity, Keff, and a corollary effective length, Leff, as derived by Nakamura (1995, 1996). This approach involves diagnosing the geometric complexity of a tracer field. Geometric complexity is indicative of advective stirring. Because stirring creates high gradients, flows with high advective stirring also have high diffusion, and stronger overall mixing. I calculate effective length from images of dye in the tank and find much higher values of Leff in the unsteady hyperbolic cases than in the other cases. Slight unsteadiness in flows involving hyperbolic points gives rise to a chaotic advection mechanism known as 'lobe dynamics'. These lobes carry fluid in and out of the recirculations, acting as extremely effective stirring mechanisms. I demonstrate the existence of these exchange lobes in the unsteady hyperbolic (figure-8) flow. The velocity field in the tank is calculated utilizing particle image velocimetry (PIV) techniques and a time series U(t) demonstrates the (forced) unsteadiness in the flow. Images of dye in the tank show exchange lobes forming at this same forcing period, and carrying fluid in and out of the recirculation. Based on the results of these experiments, I am able to confirm that, at least in this controlled environment, basic geometry has a profound effect on the mixing effectiveness of a recirculation. I demonstrate radically increased stirring and mixing in the unsteady hyperbolic flow as compared to steady flows and flows without hyperbolic points. Recirculations are ubiquitous in the world ocean; they occur on a variety of scales, in many different configurations, and at all depths. Some of these configurations involve hyperbolic points, while others do not. Chaotic advection via lobe exchange may be an important component of the mixing at multiple locations in the ocean where hyperbolic recirculation geometries exist.
by Heather E. Deese.
S.M.
31
Wells, Judith R. (Judith Roberta). "A laboratory study of localized boundary mixing in a rotating stratified fluid." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/58062.
Анотація:
Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and the Woods Hole Oceanographic Institution), 2003.Includes bibliographical references (p. 145-148).
Oceanic observations indicate that abyssal mixing is localized in regions of rough topography. How locally mixed fluid interacts with the ambient fluid is an open question. Laboratory experiments explore the interaction of mechanically induced boundary mixing and an interior body of linearly stratified rotating fluid. Turbulence is generated by a vertically oscillating horizontal bar, located at middepth along the tank wall. The turbulence forms a region of mixed fluid which quickly reaches a steady state height and collapses into the interior. The mixed layer thickness ... is independent of the Coriolis frequency f. N is the buoyancy frequency, co is the bar frequency, and the constant, Y=1 cm, is empirically determined by bar mechanics. In initial experiments, the bar is exposed on three sides. Mixed fluid intrudes directly into the interior as a radial front of uniform height, rather than as a boundary current. Mixed fluid volume grows linearly with time ... The circulation patterns suggest a model of unmixed fluid being laterally entrained with velocity, e Nhm, into the sides of a turbulent zone with height hm and width Lf ... where Lf is an equilibrium scale associated with rotational control of bar-generated turbulence. In accord with the model, outflux is constant, independent of stratification and restricted by rotation ... Later experiments investigate the role of lateral entrainment by confining the sides of the mixing bar between two walls, forming a channel open to the basin at one end. A small percentage of exported fluid enters a boundary current, but the bulk forms a cyclonic circulation in front of the bar. As the recirculation region expands to fill the channel, it restricts horizontal entrainment into the turbulent zone. The flux of mixed fluid decays with time.
(cont.) ... The production of mixed fluid depends on the size of the mixing zone as well as on the balance between turbulence, rotation and stratification. As horizontal entrainment is shut down, longterm production of mixed fluid may be determined through much weaker vertical entrainment. Ultimately, the export of mixed fluid from the channel is restricted to the weak boundary current.
by Judith R. Wells.
Ph.D.
32
Horowitz, Michael (Michael Joshua) 1962. "Western South Atlantic holocene and glacial deepwater hydrography derived from benthic foraminiferal Cd/Ca and stable carbon isotope data." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/69183.
Анотація:
Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1999.Includes bibliographical references (leaves 16-21).
Today, deep waters produced in the North Atlantic are exported through the western South Atlantic. Antarctic intermediate water (AAIW) also enters the Atlantic in this region. Circumpolar deep water (CDW) fills the depths below AAIW and above and below northern source waters. A depth transect of cores from 1567-3909 m water depth in the western South Atlantic are ideally located to monitor inter-ocean exchange of deep water, and variations in the relative strength of northern versus southern source water production. Last glacial maximum (LGM) Cd/Ca and 813C data indicate a nutrient-depleted intermediate-depth water mass. In the mid-depth western South Atlantic, a simple conversion of LGM 813C data suggests significantly less nutrient enrichment than LGM Cd/Ca ratios, but Cd/Ca and 613C data can be reconciled when plotted in CdW/ 13C space. Paired LGM Cd/Ca and S13C data from mid-depth cores suggest increasingly nutrient rich waters below 2000 m, but do not require an increase in Southern Ocean water contribution relative to today. Cd/Ca data suggest no glacial-interglacial change in the hydrography of the deepest waters of the region. To maintain relatively low Cd/Ca ratios (low nutrients) in the deepest western South Atlantic waters, and in CDW in general, during the LGM requires an increased supply of nutrient-depleted glacial North Atlantic intermediate water (GNAIW) and/or nutrient-depleted glacial Subantarctic surface waters to CDW to balance reduced NADW contribution to CDW. LGM Cd/Ca and 513C data suggest strong GNAIW influence in the western South Atlantic which in turn implies export of GNAIW from the Atlantic, and entrainment of GNAIW into the Antarctic Circumpolar current.
by Michael Horowitz.
S.M.
33
Miltenberger, Alexander Reid. "The effects of ocean eddies on tropical cyclones." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78538.
Анотація:
Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 40-41).
The purpose of this study is to understand the interactions of tropical cyclones with ocean eddies. In particular we examine the influence of a cold-core eddy on the cold wake formed during the passage of Typhoon Fanapi (2010). The three-dimensional version of the numerical Price-Weller-Pinkel (PWP) vertical mixing model has previously been used to simulate and study the cold wakes of Atlantic hurricanes. The model has not been used in comparison with observations of typhoons in the Western Pacific Ocean. In 2010 several typhoons were studied during the Impact of Typhoons on the Ocean in the Pacific (ITOP) field campaign and Fanapi was particularly well observed. We use these observations and the 3DPWP to understand the ocean cold wake generated by Fanapi. The cold wake of Fanapi was advected by a cyclonic eddy that was south of the typhoon track. The 3DPWP model outputs with and without an eddy are compared with observations made during the field campaign. These observations are compared to model outputs with eddies in a series of positions right and left of the storm track in order to study effects of mesoscale eddies on ocean vertical mixing in the cold wake of typhoons.
by Alexander Reid Miltenberger.
S.M.
34
Spiro, Jaeger Gualtiero Victor Rudi. "Stratified and stirred : monsoon freshwater in the Bay of Bengal." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122332.
Анотація:
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-121).
Submesoscale ocean dynamics and instabilities, with characteristic scales 0.1-10 kin, can play a critical role in setting the ocean's surface boundary layer thickness and associated density stratification. Submesoscale instabilities contribute to lateral stirring and tracer dispersal. These dynamics are investigated in the Bay of Bengal, motivated by the upper ocean's potentially coupled interactions with Monsoon winds and convection. The region's excess precipitation and runoff generates strong salinity gradients that typically set density fronts and stratification in the upper 50 m. Since we cannot synoptically measure currents containing fast-evolving and oscillating components across the submesoscale range, we instead analyze passive tracer distributions (spice = density-compensated temperature (T) and salinity (S) anomalies), identifying signatures of flows and testing dynamical theories.
The analysis is based on over 9000 vertical profiles of T and S measured along ~4800 km of ship tracks in the Bay of Bengal during ASIRI and MISO-BOB expeditions in 2013, 2015, and 2018. Observations in the surface mixed layer reveal ~1 km scale-selective correlation of surface T and S, with compensation reducing cross-front density gradients by ~50%. Using a process study ocean model, we show this is caused by submesoscale instabilities slumping fronts, plus surface cooling over the resultant enhanced salinity stratification, potentially thwarting the forward cascade of energy. In the stratified interior, we present a spectral analysis of horizontal spice variance statistics from wavenumber k ~0.01 cpkm to ~1 cpkm. At scales <10 km, stratified layers that are closer to the surface exhibit redder passive tracer spectra (power spectra k⁻³, gradient spectra k⁻¹) than predicted by quasi-geostrophic or frontogenetic theories.
Complimentary observations reveal spice patterns with multiple, parallel, ~10 m thin layers, crossing isopycnals with O(10⁻⁴) slopes, coherent over at least 30-80 kin, with coincident layers of stratification anomalies. Comparison with shear measurements, and a numerical process study, suggest that both submesoscale sheared eddies, and thin near-inertial waves, form such layers. Fast formation timescales and large aspect ratios suggest they enhance horizontal mixing by shear dispersion, reducing variance at ~1-10 km scales.
by Gualtiero Victor Rudi Spiro Jaeger.
Ph. D.
Ph.D. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)
35
Gerbi, Gregory Peter. "Observations of turbulent fluxes and turbulence dynamics in the ocean surface boundary layer." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45778.
Анотація:
Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008.Includes bibliographical references (p. 110-119).
This study presents observations of turbulence dynamics made during the low winds portion of the Coupled Boundary Layers and Air-Sea Transfer experiment (CBLAST-Low). Observations were made of turbulent fluxes, turbulent kinetic energy, and the length scales of flux-carrying and energy-containing eddies in the ocean surface boundary layer. A new technique was developed to separate wave and turbulent motions spectrally, using ideas for turbulence spectra that were developed in the study of the bottom boundary layer of the atmosphere. The observations of turbulent fluxes allowed the closing of heat and momentum budgets across the air-sea interface. The observations also show that flux-carrying eddies are similar in size to those expected in rigid-boundary turbulence, but that energy-containing eddies are smaller than those in rigid-boundary turbulence. This suggests that the relationship between turbulent kinetic energy, depth, and turbulent diffusivity are different in the ocean surface boundary layer than in rigid-boundary turbulence. The observations confirm previous speculation that surface wave breaking provides a surface source of turbulent kinetic energy that is transported to depth where it dissipates. A model that includes the effects of shear production, wave breaking and dissipation is able to reproduce the enhancement of turbulent kinetic energy near the wavy ocean surface. However, because of the different length scale relations in the ocean surface boundary layer, the empirical constants in the energy model are different from the values that are used to model rigid-boundary turbulence. The ocean surface boundary layer is observed to have small but finite temperature gradients that are related to the boundary fluxes of heat and momentum, as assumed by closure models. However, the turbulent diffusivity of heat in the surface boundary layer is larger than predicted by rigid-boundary closure models. Including the combined effects of wave breaking, stress, and buoyancy forcing allows a closure model to predict the turbulent diffusivity for heat in the ocean surface boundary layer.
by Gregory Peter Gerbi.
Ph.D.
36
Fong, Derek Allen. "Dynamics of freshwater plumes: observations and numerical modeling of the wind-forced response and alongshore freshwater transport." Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/58510.
Анотація:
Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1988.Includes bibliographical references (leaves 163-172).
A freshwater plume often forms when a river or an estuary discharges water onto the continental shelf. Freshwater plumes are ubiquitous features of the coastal ocean and usually leave a striking signature in the coastal hydrography. The present study combines both hydrographic data and idealized numerical simulations to examine how ambient currents and winds influence the transport and mixing of plume waters. The first portion of the thesis considers the alongshore transport of freshwater using idealized numerical simulations. In the absence of any ambient current, the downstream coastal current only carries a fraction of the discharged fresh water; the remaining fraction recirculates in a continually growing "bulge" of fresh water in the vicinity of the river mouth. The fraction of fresh water transported in the coastal current is dependent on the source conditions at the river mouth. The presence of an ambient current augments the transport in the plume so that its freshwater transport matches the freshwater source. For any ambient current in the same direction as the geostrophic coastal current, the plume will evolve to a steady-state width. A key result is that an external forcing agent is required in order for the entire freshwater volume discharged by a river to be transported as a coastal current. The next section of the thesis addresses the wind-induced advection of a river plume, using hydrographic data collected in the western Gulf of Maine. The observations suggest that the plume's cross-shore structure varies markedly as a function of fluctuations in alongshore wind forcing. Consistent with Ekman dynamics, upwelling favorable winds spread the plume offshore, at times widening it to over 50 km in offshore extent, while downwelling favorable winds narrow the plume width to a few Rossby radii. Near-surface current meters show significant correlations between cross-shore currents and alongshore wind stress, consistent with Ekman theory. Estimates of the terms in the alongshore momentum equation calculated from moored current meter arrays also indicate an approximate Ekman balance within the plume. A significant correlation between alongshore currents and alongshore wind stress suggests that interfacial drag may be important. The final section of the thesis is an investigation of the advection and mixing of a surface-trapped river plume in the presence of an upwelling favorable wind stress, using a three-dimensional model in a simple, rectangular domain. Model simulations demonstrate that the plume thins and is advected offshore by the cross shore Ekman transport. The thinned plume is susceptible to significant mixing due to the vertically sheared horizontal currents. The first order plume response is explained by Ekman dynamics and a Richardson number mixing criterion.
by Derek Allen Fong.
Ph.D.
37
Lerisson, Gaétan. "Stabilité d'une onde de gravité interne, analyse locale, globale et croissance transitoire." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLX017/document.
Анотація:
Dans les océans profonds linéairement stratifiés, la déstabilisation des ondes de gravité internes est importante car elle contribue probablement au mélange turbulent et à la circulation thermohaline.À l'aide de simulations numériques directes, nous créons un faisceau d'onde interne progressive. Cette situation est équivalente à une onde produite par l'oscillation de la marée sur une topographie sous-marine. Nous retrouvons les résultats expérimentaux obtenus par cite{Bourget13} : le faisceau se déstabilise en un mode petite échelle. Nous regardons l'effet d'un écoulement horizontal moyen sur cette instabilité en prenant soin d'abaisser la fréquence de forçage afin de compenser l'effet doppler et de conserver localement la même onde. Un cas limite apparaît lorsque le forçage devient stationnaire, ce qui équivaut à une onde de sillage issue d'un écoulement constant au dessus d'une topographie.Les écoulements à petite vitesse voient une instabilité petite échelle similaire au cas marée alors que les écoulement intermédiaires restent stables. Les écoulements plus rapides (jusqu'au cas sillage) voient, par contre, une instabilité bien plus grande échelle que celle dans le cas marée. Cette sélection d'échelle est robuste aux variations du nombre de Froude, de Reynolds, de la taille du faisceau ou de l'angle de l'onde.Nous montrons que ces instabilités peuvent être décrites comme des triades résonantes et que les différentes échelles correspondent à différentes branches triadiques. Nous confirmons la présence de cas stables pour des vitesses intermédiaires en calculant les modes propres comme des modes de Floquet à l'aide d'un algorithme d'Arnoldi--Krylov, et en montrant qu'ils sont associés à des taux de croissance négatifs.Le cas sillage est instable et nous le stabilisons par une méthode deselective frequency damping cite{Akervik06} afin d'obtenir un écoulement de base stationnaire autour duquel nous calculons les perturbations optimales qui maximisent l'énergie totale à différents horizons temporels. Pour des horizons courts, la perturbation optimale est petite échelle alors que pour des horizons longs, elle est grande échelle et converge vers la solution non-linéaire obtenue précédemment. Les horizons courts voient une instabilité triadique petite échelle advectée par l'écoulement et les horizons longs développent une instabilité d'une branche triadique grande échelle capable de se maintenir dans le faisceau malgré l'écoulement.Nous interprétons cette sélection de mode par le biais de la théorie des instabilités absolue ou convective. Dans le cas de l'onde de sillage l'instabilité grande échelle est absolue alors que la petite échelle est convective (et domine la croissance transitoire puisque son taux de croissance local est supérieur). Les rôles s'inversent dans le cas marée et l'instabilité petit échelle devient absolue alors que la grande échelle est convective. Nous confirmons cette hypothèse en calculant la réponse impulsionnelle d'une onde plane monochromatique dans un domaine 2Dpériodique. L'évolution spatio-temporelle d'une perturbation localisée en temps et en espace montre la formation de trois paquets d'onde, chacun étant associé à une branche triadique que nous identifions par une extension de la théorie triadique prenant en compte un désaccordage cite{McEwan77} et permettant de calculer la vitesse de groupe des sommets des paquets. En calculant ensuite le taux de croissance absolu le long de rayons à x/t et z/t constant, nous validons notre hypothèseInternal gravity waves that exist in a continuously stratified fluid are particularly important in the ocean. They transport energy and are thought to generate turbulent mixing, which contribute to the deep ocean circulation.We generate an internal wave beam that propagates in a continuously stratified fluid with direct numerical simulations. This situation is equivalent to a tidal wave, where the tidal flow oscillates over a topography and generates a wave. Experimental results obtained by cite{Bourget13} are recovered, ie. the beam destabilizes into a small scale mode. We consider the effect of an horizontal mean flow on the instability and lower the forcing frequency in order to compensate for the doppler effect and to keep locally the same wave. A limit case appears when the forcing becomes stationary. This case is equivalent to a lee wave appearing when a stratified fluid flows over a topography.For small mean flow, small scale instabilities develop as in the tidal case. The beam then stabilizes at intermediate mean flows and destabilizes again for increasing flow speed. At this second threshold, down to the lee wave case, the instability is of much larger scale than for the tidal case. Varying the Reynolds number, the Froude number, the wave angle or the beam size doesn't affect the instability scale selection : a small scale instability in the tidal regime, and large scale instability in the lee regime.We show that the instability mechanism may be interpreted using the triadic instability. Scale selection corresponds to different branches of triadic resonance. We confirm the presence of a stability region for intermediate value of the mean advection velocity by computing the linear eigenmode as Floquet mode with an Arnoldi-Krylov technique and show that the leading eigenmode has a negative growth rate.In the lee wave, case the flow is unstable and a selective frequency damping method cite{Akervik06} is used to compute a steady base flow. We then implement a linear direct-adjoint method to compute the optimal perturbations that maximizes the total energy at different time horizons. At short time horizon, the optimal perturbation is small scale while at large time the perturbation switches to a large scale solution and converges to the large scale mode observed through the nonlinear simulations. Short time transients correspond to the small scale triadic instability advected by the flow whereas the long time large scale instability corresponds to large scale branch of the triadic instability that is able to sustain the flow.We propose an interpretation of the selection of these different instabilities in term of absolute and convective instability. In the case of the lee wave, the large scale instability is absolute whereas the small scale instability is convective (and dominates the short time transient growth because it has a larger local growth rate). When the mean flow is varied, the properties of small scale and large scale instabilities exchange: in the tidal case the short scale instability is absolute and the large scale convective. This conjecture is confirmed by computing the impulse response around a plane monochromatic internal gravity wave in an extended two dimensional periodic domain. The spatio temporal evolution of a perturbation localized in space and time points out the formation of three different wave packets corresponding to different branches of triadic instability. Using the triadic theory with finite detuning cite{McEwan77},we derive the group velocity at the maximum growth rate of the three different branches of triadic instability and find a good agreement with the velocity of the three wave paquet maxima in the impulse response. Analyzing the impulse response along rays, i.e. at x/t and z/tconstant, we compute the absolute growth rate along all possible rays and validate our conjecture
38
Abernathey, Ryan (Ryan Patrick). "Mixing by ocean eddies." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70772.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 163-175).
Mesoscale eddies mix and transport tracers such as heat and potential vorticity laterally in the ocean. While this transport plays an important role in the climate system, especially in the Southern Ocean, we lack a, comprehensive understanding of what sets mixing rates. This thesis seeks to advance this understanding through three related studies. First, mixing rates are diagnosed from an eddy-resolving state estimate of the Southern Ocean, revealing a meridional cross-section of effective diffusivity shaped by the interplay between eddy propagation and mean flow. Effective diffusivity diagnostics are then applied to quantify surface mixing rates globally, using a, kinematic model with velocities derived from satellite observations; the diagnosed mixing rates show a rich spatial structure, with especially strong mixing in the tropics and western-boundary-current regions. Finally, an idealized numerical model of the Southern Ocean is analyzed, focusing on the response to changes in win( stress. The sensitivity of the meridional overturning circulation to the wind changes demonstrates the importance of properly capturing eddy mixing rates for large-scale climate problems.
by Ryan Abernathey.
Ph.D.
39
Zika, Jan David Climate & Environmental Dynamics Laboratory Faculty of Science UNSW. "Quantifying ocean mixing from hydrographic data." Awarded by:University of New South Wales. Climate & Environmental Dynamics Laboratory, 2010. http://handle.unsw.edu.au/1959.4/44872.
Анотація:
The relationship between the general circulation of the ocean and, along-isopycnal and vertical mixing is explored. Firstly, advection down isopycnal tracer gradients is related to mixing in specific regions of the ocean. Secondly, a general inverse method is developed for estimating both mixing and the general circulation. Two examples of down gradient advection are explored. Firstly the region of Mediterranean outflow in the North Atlantic. Given a known transport of warm salty water out of the Mediterranean Sea and the mean hydrography of the eastern North Atlantic, the vertical structure of the along-isopycnal mixing coefficient, K, and the vertical mixing coefficient, D, is revealed. Secondly, the Southern Ocean Meridional Overturning Circulation, SMOC, is investigated. There, relatively warm salty water is advected southward, along-isopycnals, toward fresher cooler surface waters. The strength and structure of the SMOC is related to K and D by considering advection down along-isopycnal gradients of temperature and potential vorticity. The ratio of K to D and their magnitudes are identified. A general tool is developed for estimating the ocean circulation and mixing; the \textit{tracer-contour inverse method}. Integrating along contours of constant tracer on isopycnals, differences in a geostrophic streamfunction are related to advection and hence to mixing. This streamfunction is related in the vertical, via an analogous form of the depth integrated thermal wind equation. The tracer-contour inverse method combines aspects of the box, beta spiral and Bernoulli methods. The tracer-contour inverse method is validated against the output of a layered model and against in-situ observations from the eastern North Atlantic. The method accurately reproduces the observed mixing rates and reveals their vertical structure.
40
Dusenberry, Jeffrey A. (Jeffrey Allen). "Picophytoplankton photoacclimation and mixing in the surface oceans." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38740.
41
Damerell, Gillian. "Aspects of southern ocean transport and mixing." Thesis, University of East Anglia, 2012. https://ueaeprints.uea.ac.uk/45642/.
Анотація:
Understanding and quantifying the circulation of the oceans and the driving mechanisms thereof is an important step in developing models which can accurately predict future climate change. In particular, model studies have shown that the spatial variability of diapycnal diffusivity, which represents the rate at which deep water returns to shallower depths by means of turbulent diapycnal mixing, is a critical factor controlling the strength and structure of the circulation. Efforts are therefore ongoing to measure diffusivity as extensively as possible, but temporal variability in diffusivity has not been widely addressed. Results from three Southern Ocean studies are presented in this thesis. Firstly, a high resolution hydrographic survey carried out on the northern flank of the Kerguelen Plateau identifies a complex meandering current system carrying a total eastward volume transport of 174 ± 22 Sv, mostly associated with the blended Subtropical Front/Subantarctic Front. Significant water mass transformation across isopycnals is not required to balance the budgets in this region. Secondly, results are presented which cast doubt on the advisability of using density profiles acquired using Conductivity-Temperature-Depth instruments to estimate diapycnal diffusivity (an attractive proposition due to low cost and widespread data availability) in areas of weak stratification such as the Southern Ocean, because the noise characteristics of the data result in inaccurate diffusivity estimates. Finally, a method is developed for estimating diffusivity from profiles of velocity shear acquired by moored acoustic Doppler current profilers. An 18-month time series of diffusivity estimates is derived with a median of 3.3 × 10−4 m2 s−1 and a range of 0.5 × 10−4 m2 s−1 to 57 × 10−4 m2 s−1. There is no significant signal at annual or semiannual periods, but there is evidence of signals at periods of approximately fourteen days (likely due to the spring-neaps tidal cycle), and at periods of 3.8 and 2.6 days most likely due to topographically-trapped waves propagating around the local seamount. More widespread application of this method would allow for an assessment of natural climate variability in diapycnal diffusivity.
42
Chu, Chi-keung Paul. "Mixing of turbulent advected line puffs /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B19041597.
43
Figueroa, Rodríguez Jesús Manuel. "Dynamics and mixing in the Upper Ocean Layer." Doctoral thesis, Universitat de Girona, 2005. http://hdl.handle.net/10803/7807.
Анотація:
S'estudia la resposta de la capa de barreja oceànica al forçament atmosfèric considerant dades obtingudes durant 12 dies d'abril del 2001 a 42 estacions a través de l'Atlàntic nord seguint aproximadament la latitud de 53ºN. Aquestes dades inclouen, a més de variables atmosfèriques, mesures de CTD, velocitats amb ADCP i dades de microestructura obtingudes amb un perfilador de caiguda lliure. En aquest últim cas, s'han desenvolupat tècniques de processament de les dades que també es presenten aquí.El transsecte estudiat segueix la posició climatològica del rotacional mitjà anual
del vent igual a zero i travessa el corrent del Labrador i algunes branques i meandres
del Corrent Atlàntic Nord. El forçament atmosfèric es va caracteritzar per vents intensos i fluxos superficials de calor negatius, tot i que, tal com es dedueix de la comparació del gruix de la capa de barreja amb la longitud de Monin-Obukov, la barreja induïda pel vent va dominar sobre la convectiva durant tot el transsecte.
The response of the mixed layer depth (MLD) to short-term (synoptic) variations of atmospheric forcing in the North Atlantic Ocean was analysed using CTD data, microstructure profiling, ADCP velocities and atmospheric measurements taken
during the last 12 days of April 2001 at 42 stations located close to 53ºN. The transect followed the climatological position of zero annually-averaged wind stress curl (WSC), crossing the Labrador Current and several branches and meanders of the North Atlantic Current. Atmospheric forcing was characterized by relatively high wind speeds and negative surface heat balance.
It is described the variability of the mixed layer and some parameterizations on different lengthscales are proposed. The vertical structure of TKEDR is analyzed and two closures schemes (Munk-Anderson type) are proposed. Finally it is explored the momentum rate of transference from wind to the ocean interior.
44
Boland, Emma Joan Douglas. "Jets, mixing, and topography in the Southern Ocean." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/245073.
Анотація:
The Southern Ocean holds a unique place in our planet. It is home to the world’s longest and strongest ocean current, the Antarctic Circumpolar Current (or ACC), which is formed of jets (alternating velocity structures), thought to be significant surface transport barriers. The dynamical processes (particularly mixing processes) in the Southern Ocean are crucial to driving the global overturning circulation, which is in turn responsible for the global transport of heat, CO2, and nutrients. Despite the evident importance of the Southern Ocean to current and future climate, the important dynamical processes that occur there are poorly understood. This thesis attempts to contribute towards the understanding of some of the open questions in Southern Ocean dynamics. In particular, we investigate the effect that topography might have on the jets that form the ACC, with regards to their formation and in particular, their transport properties. Through a quasi-geostrophic model we investigate the properties of jets that form over a zonal slope in bottom topography, and find that the jets become tilted, aligning perpendicular to the large-scale barotropic potential vorticity gradient. As the jets tilt more, they become significantly more energetic, corresponding with an increase in across-jet transport. We compare various theories regarding the formation of such jets, involving linear analysis of the system. It is found that the analytical form of the Rossby wave frequencies correctly predicts the anisotropy of the energy spectra of simulations, and so the jet direction. Additionally, there is a need to characterise accurately the isopycnal mixing occurring throughout the Southern Ocean. We utilise satellite measurements to estimate isopycnal diffusivities in the Southern Ocean in two different studies. Using an effective diffusivity diagnostic to extend a previous study, we find reduced surface horizontal mixing at the latitudes of the ACC core. By comparing a tracer advection simulation with measurements from an experiment in the Southern Ocean, we find that simulations with a vertically averaged horizontal diffusivity of 20m2s−1 best match observations in the Pacific sector of the ACC.
45
朱智強 and Chi-keung Paul Chu. "Mixing of turbulent advected line puffs." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B29986758.
46
Banks, Helene Theresa. "Intrusions and mixing in the Western Equatorial Pacific Ocean." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243128.
47
Heubel, Eric Vincent. "Parameter estimation and adaptive modeling studies in ocean mixing." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/46155.
Анотація:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2008.Includes bibliographical references (p. 119-121).
In this thesis, we explore the different methods for parameter estimation in straightforward diffusion problems and develop ideas and distributed computational schemes for the automated evaluation of physical and numerical parameters of ocean models. This is one step of "adaptive modeling." Adaptive modeling consists of the automated adjustment of self-evaluating models in order to best represent an observed system. In the case of dynamic parameterizations, self-modifying schemes are used to learn the correct model for a particular regime as the physics change and evolve in time. The parameter estimation methods are tested and evaluated on one-dimensional tracer diffusion problems. Existing state estimation methods and new filters, such as the unscented transform Kalman filter, are utilized in carrying out parameter estimation. These include the popular Extended Kalman Filter (EKF), the Ensemble Kalman Filter (EnKF) and other ensemble methods such as Error Subspace Statistical Estimation (ESSE) and Ensemble Adjustment Kalman Filter (EAKF), and the Unscented Kalman Filter (UKF). Among the aforementioned recursive state estimation methods, the so-called "adjoint method" is also applied to this simple study. Finally, real data is examined for the applicability of such schemes in real-time forecasting using the MIT Multidisciplinary Simulation, Estimation, and Assimilation System (MSEAS). The MSEAS model currently contains the free surface hydrostatic primitive equation model from the Harvard Ocean Prediction System (HOPS), a barotropic tidal prediction scheme, and an objective analysis scheme, among other models and developing routines. The experiment chosen for this study is one which involved the Monterey Bay region off the coast of California in 2006 (MB06). Accurate vertical mixing parameterizations are essential in this well known upwelling region of the Pacific. In this realistic case, parallel computing will be utilized by scripting code runs in C-shell. The performance of the simulations with different, parameters is evaluated quantitatively using Pattern Correlation Coefficient, Root Mean Squared error, and bias error. Comparisons quantitatively determined the most adequate model setup.
by Eric Vincent Heubel.
M.Eng.
48
Mitsis, Christos. "Lagrangian studies, circulation and mixing in the Southern Ocean." Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/45250/.
Анотація:
Oceans play a vital role as one of the major components of Earth's climate system. The study of oceanic processes and the complexity inherent in dynamic ows is essential for understanding their regulatory character on the climate's variability. A key region for the study of such intrinsic oceanic variability is the Southern Ocean. In the form of a wind-driven, zonally unbounded, strong eastward ow, the Antarctic Circumpolar Current (ACC) circumnavigates the Antarctic continent connecting each of the ocean basins. The dynamics of the ACC, which is characterised by the absence of land barriers, apart from when crossing Drake Passage, have long been a topic of debate [Rintoul et al., 2001]. The main interests of this study focus on inferring and mapping the dynamic variability the ACC exhibits by means of transient disturbances [Hughes, 2005] (such as mesoscale eddies) and subsequent mixing from Lagrangian trajectories. The distribution of eddy transport and intensity, the mixing of conservative quantities and ow dynamics through to the interaction of eddy kinetic energy, mean ow and topography are examined. The sparseness of observations in the Southern Ocean and the necessity to understand the role of the oceanic circulation in the climate by a holistic approach highlights computational ocean circulation models as indispensable. In the context of this study, output from the run401 of the Ocean Circulation and Climate Advance Model (OCCAM) 1/12� ocean model, developed at the U.K. National Oceanography Centre, is utilised. In order to deduce the temporal and spatial variability of the ow dynamics, as well as its vertical distribution, simulation of monthly releases of passive particles using di�erent schemes (i.e. cluster or linear alignment) on isobaric and isoneutral surfaces was conducted. An analysis of the Lagrangian trajectories reveals the characteristics of the dynamics that control the ow and depict regions of enhanced eddy activity and mixing. The model's ability to simulate real oceanic ows is established through comparison with a purposeful release of the tracer CF3SF5, which is conducted as part of the DIMES experiment (http://dimes.ucsd.edu/). We �nd that topography plays a fundamental role in the context of Southern Ocean mixing through the association of high EKE regions, where the interaction of vortical elements and multi �lamented jets in non-parallel ows supports an e�ective mechanism for eddy stirring, resulting in the enhanced dispersion of particles. Suppression of mixingin regions where the ow is delineated by intensi�ed and coherent, both in space and time, jets (strong PV gradients) signifying the separation of the ow in di�erentiated kinematic environments, is illustrated. The importance of a local approximation to mixing instead of the construction of zonal averages is presented. We present the caveats of classical di�usion theory in the presence of persistent structures and �nd that values of 1000-2000 m2 s
49
Carse, Fiona. "Lake and ocean vertical mixing using sulphur hexafluoride tracer techniques." Thesis, University of East Anglia, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327480.
50
Ott, Michael William. "Mixing and secondary circulation in Juan de Fuca Strait." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ52768.pdf.