Dissertations / Theses on the topic 'Eddies'
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1
Abernathey, Ryan (Ryan Patrick). "Mixing by ocean eddies." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70772.
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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.
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Cenedese, Claudia. "Baroclinic eddies over topography." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624104.
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Athanasiadis, Panos J. "Teleconnections and transient eddies." Thesis, University of Reading, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493965.
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The subject of this thesis is the dynamics of teleconnections and mid-latitude stationary eddies, key components of the structure and variability of the extratropical general circulation. Deepening our understanding of their dynamics is of particular importance in the context of predicting and explaining possible climate changes.
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Haines, K. "Long-lived eddies in planetary atmospheres." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38343.
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An, Byoung Woong. "Modelling outflows, coastal currents and eddies." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446475/.
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Several types of flows driven by outflows on the continental shelf are examined mathematically and numerically. Within a quasigeostrophic framework, a variety of vertical structures and topographies are used. Features are explained in terms of potential vorticity conservation. The combined effects of topography and anomalous vorticity of the outflow are studied. First, shelf-like topography is considered. The role of topographic wave radiation is studied using the linearised barotropic potential vorticity equation for a weak outflow with zero vorticity. Contour dynamics is used for stronger outflows with relative vorticity. Next, the effects of anomalous vorticity in driving such coastal currents are studied using 11/2-layer model and its interaction with topography. Simulations show that the strong tendency for the development of anticyclonic eddy near topographic change. Two-layer outflows and their interaction with topography are examined. Purely buoyancy driven outflows are considered in which only one of two layers enters the flow domain. Purely barotropic outflows are also considered. Simulations show the development of eddies by interaction with topography in the lower fluid. The effect of topography whose gradient lies perpendicular to the coastline on coastal currents and eddies is investigated. The formation of dipole eddies is found to be a robust feature when the coastal current interacts with the topography depending on the sign of the topographic gradient. The stability of a two-layer converging/diverging coastal jet associated with piecewise constant potential vorticity is studied numerically. Baroclinic instability is demonstrated. The origin of the instability appears first at the coast, and may explain the meandering and eddying associated with detaching western boundary currents. The final study revisits the barotropic outflow problem. Owing to boundary layer separation at the exit, the outflow may consist of a dipolar structure. The interaction of this dipole with shelf-like topography is studied numerically.
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Burns, Helen. "Diabatic eddies in idealised channel models." Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/424757/.
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The Southern Ocean is a unique and climatically important region where mesoscale eddies are of first order importance. The circulation of the Southern Ocean controls the amount of carbon stored in the ocean and is an integral part of the worlds global overturning circulation. It is therefore of great importance to understand the dynamics of the Southern Ocean and the possible response of the overturning circulation to changing forcing i.e. climate change. Because of the role eddies play in setting that circulation, the dynamics are still not fully understood. This thesis explores one poorly understood aspect of the Southern Ocean; dia- batic eddies. Using the Massachusetts Institute of Technology General Circulation Model (MITgcm) to set up an idealised channel we close the northern boundary which causes the Southern Ocean overturning to collapse. This is to be expected as the circulation is part of the global overturning and must be connected to the rest of the world’s ocean. We use Transformed Eulerian Mean (TEM) theory to suggest this collapse is achieved via diabatic eddies altering the effective surface buoyancy forcing. We then alter the northern boundary condition to show that diabatic eddies can be related to the northern boundary stratification. However the response of the diabatic eddies is also dependent on the surface forcing, partic- ularly the sense of the forcing: changing from fixed-fluxes to surface restoring can have dramatic effects. Surface restoring alters the dynamics of the mixed layer, eddy compensation and saturation. This suggests that when exploring Southern Ocean dynamics in regional models, the effect of the imposed boundary conditions must always be considered. Our results suggest if the background stratification is altered we may see a very different circulation in the Southern Ocean, but to what extent would also depend on the response of the atmosphere and hence the surface forcing.
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Hall, C. "Cyclonic Eddies in the Cape Basin." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/6586.
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A great deal of attention has been paid to the inter-ocean exchange of thermohalineproperties in the Agulhas Retroflection region. Recent observations have shown thatthe highly energetic field of the southern half of the Cape Basin consists of bothcyclonic and anticyclonic eddies. These eddies interact with each other, resulting inthe vigorous stirring of these water mass. Investigations have shown that the cycloniceddies tend to be smaller and outnumber the anticyclonic rings. Nonetheless, verylittle is known of their characteristics and the nature in which they are formed. Usingremote sensing data, confirmed with hydrographic data, this study determines thelocation, frequency and seasonality of cyclonic eddy formation; their size, trajectoriesand lifespan; physical components and associations with Agulhas Rings.Cyclonic eddies were seen to split, merge and link with other cyclonic eddies, withsplitting events creating child cyclonic eddies. The 105 parent and 157 child cycloniceddies identified during this study show that an average of II parent and 17 childcyclonic eddies were formed annually. 31.58 % follow an overall west-southwestdirection, with 27.37 % translocating west north-westward. Poleward translocationspeeds average at 0.3 kIn/day, whereas translocation speeds obtained from alldirectional components averages at 2.153 kIn/day for parent and 2.975 km/day forchild cyclonic eddies. Parent cyclonic eddies lived for approximately 254 days,whereas child cyclonic eddies survived for a mean of 188 days. Of note was asignificant variation of lifespan between parent and child cyclonic eddies formed inboth the north and south of the study area. 77 % of northern and 93 % of southerncyclonic eddies were formed directly adjacent to positive sea level anomalies orAgulhas Rings, resulting in an total overall association of 82.93 % parent and 89.63 %child cyclonic eddies. Cyclonic eddy groups were seen to merge at a rate of 16.38parent and 14 child cyclonic eddies per year, whereas topography appeared to affectthe demise of 17.00 % of the investigated cyclonic eddies.Therefore this study may form a basis for further investigations into the influenceCape Basin cyclonic eddies have on the meridional transfer of heat, salt, nutrients,oxygen and carbon concentrations in the South-East Atlantic Ocean. A more in-depthstudy using model outputs and targeted in situ hydrographical data would againenhance cyclonic eddy knowledge.
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Ring, Michael J. 1979. "The role of eddies in buoyancy flux." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/114316.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2001.Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2001.
Cataloged from PDF version of thesis.
Includes bibliographical references (page 35).
This thesis explores the role of eddies in determining the stratification of the ocean through a laboratory experiment. The experiment uses a dual-tank apparatus, with a smaller tank sitting inside the larger tank. Both tanks sit on a rotating turntable, which simulates the rotation of Earth. During the experiment, salty water is pumped from the outer tank through small holes in the base of the inner tank, which is initially filled with fresh water. The evolution of the dense fluid in the inner tank is observed, with particular regard to the number of eddies that form. These observations are checked against theoretical predictions, derived from analysis of buoyancy flux, for the number of eddies expected to form.
by Michael J. Ring.
S.B.
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Lewis, Stephen Richard. "Long-lived eddies in the atmosphere of Jupiter." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329956.
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Miltenberger, Alexander Reid. "The effects of ocean eddies on tropical cyclones." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78538.
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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.
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Jordan, Stephen Arthur. "The large-eddy simulation of incompressible flows in simple and complex geometries." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-10022007-145351/.
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Doddi, Sai Kumar. "Validation of detached eddy simulation using LESTool for homogenous turbulence." Lexington, Ky. : [University of Kentucky Libraries], 2004. http://lib.uky.edu/ETD/ukymeen2004t00143/Sai%5FThesis.pdf.
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Thesis (M.S.)--University of Kentucky, 2004.Title from document title page (viewed June 21, 2004). Document formatted into pages; contains xii, 117 p. : ill. Includes abstract and vita. Includes bibliographical references (p. 113-116).
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Carpenter, Glen H. "Surface circulation associated with the Mindanao and Halmahera Eddies." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27297.
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Adcock, Susan T. "A parameterisation of geostrophic eddies over variable bottom topography." Thesis, University of Reading, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314318.
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Gunn, Kathryn Louise. "Time-lapse acoustic imaging of oceanic fronts and eddies." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/284560.
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Seismic reflection surveying is used to generate acoustic images of the water column. This technique employs conventional multi-channel equipment which is used to image the solid Earth. In the water column, acoustic impedance contrasts are produced by variations in temperature and, to some extent, salinity. Acoustic impulses generated by an array of airguns suspended behind a vessel are reflected from these contrasts and recorded on long cables of hydrophones that are towed below the sea-surface. In this way, two- and three-dimensional images of thermohaline circulation can be generated. Critically, these images have equal vertical and horizontal resolutions of \textit{O}(10)~m. Here, I describe, process, and analyse a calibrated two-dimensional seismic survey from the Bellingshausen Sea of the Southern Ocean and a three-dimensional seismic survey from the Brazil-Falkland Confluence located offshore Uruguay. First, the Bellingshausen survey was designed to image the thermohaline structure across the west Antarctic shelf where warm-core eddies are reported. Processed and calibrated seismic images reveal the detailed thermohaline structure of Circumpolar Deep Water. Many warm-core eddies are observed, which have diameters of 1--12~km and thicknesses of 100--200~m. Pre-stack analysis demonstrates that this eddy field is being advected onto the shelf at speeds of \textit{O}(0.1)~m~s$^{-1}$. An iterative inverse modelling procedure is used to convert reflectivity into temperature and salinity, which confirms that the eddies have anomalously warm centres (i.e. $\sim$1$^{\circ}$C). These results have significant implications for ice shelf melting. Secondly, the Uruguay survey is used to investigate a large-scale frontal system. Although this system has been studied using hydrographic methods, these studies either have limited spatial resolution or have restricted depth penetration. The three-dimensional seismic survey, which was acquired in a `racetrack' pattern, permits the volume to be interrogated. Since the frontal system migrates southwestwards at a speed of \textit{O}(10)~km~day$^{-1}$, this survey is time-lapse in nature. Processed images reveal a band of dipping reflections that extend to depths of $\sim$2000~m. These reflections represent the frontal interface between the Brazil and Falkland currents. Physical oceanographic properties are calculated for images that cross this front. On the warm side of the front, the water mass is characterised by flat and continuous reflectivity. On the cold side of the front, the water mass is characterised by deformed reflectivity on all scales. Pre-stack analysis suggests that near-surface flow at the frontal interface is convergent. Between 0.5 and 1~km depth, a substantial eddy that is 30~km long and 250~m thick is visible on the cold side of the front. Detailed mapping suggests that this eddy grew and decayed over a period of 6~days. Its observed scale and duration are inconsistent with analytical and numerical studies of intra-thermocline eddies. Nevertheless, its duration is consistent with scaling arguments of frictional spin-down. Spatial and temporal distributions of mixing rates (i.e. diapycnal diffusivities) are estimated by spectrally analysing vertical displacements of automatically tracked reflections. Both internal wave and turbulent regimes are identifiable. Recovered diapycnal diffusivities are of \textit{O}($10^{-6}$--$10^{-2.2}$)~m$^{2}$~s$^{-1}$, consistent with hydrographically determined estimates. Mixing is suppressed and enhanced on the warm and cold sides of the front, respectively. Seismic Oceanography has considerable potential to quantify aspects of thermohaline circulation on multiple scales.
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O'Reilly, Bevan James. "Phytoplankton associated with mesoscale eddies in the Mozambique Channel." Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1010967.
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The study undertaken was an attempt to provide information on the effect that oceanographic features common in the Mozambique Channel have on primary production. Oligotrophic conditions dominated the Mozambique Channel at the time of sampling and the introduction of nutrients into the euphotic zone by upwelling processes were identified as cyclonic eddies. Differences in physico-chemical variables between surface and F-max across all sites proved to be stronger than the physico-chemical variables between 4 grouped oceanographic features. This was revealed by stronger variations in phytoplankton community structure and chlorophyll a concentration between surface and F-max compared to oceanographic features sampled. One of the hypotheses presented for the study was that diatoms would dominate phytoplankton communities within a cyclonic eddy. This was not the case as the coccolithophorid, Emiliania huxleyi Lohmann (Hay and Mohler 1967) dominated F-max and surface water in the cyclonic eddies and most other sites. Phytoplankton community structure did not differ significantly between the oceanographic features sampled which contradicted another one of hypotheses presented in the study. Chlorophyll a concentration in surface water of the cyclonic eddies was significantly higher than in surface waters within the anti-cyclonic eddy. F-max was not significantly different in phytoplankton biomass between these two system types. The cyclonic eddies and anti-cyclone had similar phytoplankton diversity which did not verify the hypothesis that there would be less phytoplankton species diversity within cyclonic eddies compared to the anti-cyclonic eddy. Phytoplankton community structure differed between F-max (depth at which maximum chlorophyll a is found) and the surface. This phytoplankton community difference was linked to differences in physico-chemical variables between the two depths. The diatoms Thalassionema nitzschioides, Pseudo-nitzschia sp.A, Pseudo-nitzschia sp.B, Thalassiosira sp.C, Thalassiosira sp.E, Bacteriastrum furcatum, Guinardia cylindrus, Nitzschia closterium, Hemiaulus hauckii, and Nitzschia braarudii revealed the only discernible ecological similarity amongst phytoplankton species across all sites and depths. This is important as it revealed that these species were regularly found occupying similar depths and potentially similar physico-chemical ranges in the water column which suggest these diatom species responded to a dominant source of variation. Distribution patterns of species and of ecologically defined groups support the hypothesis that diatom species and assemblages are good indicators of the changing character of an upwelling system. These statements lead to the assumption that the diatom grouping found in this study indicates areas of upwelling where water temperatures are reduced and nutrients are more readily available. One must keep in mind that ordination techniques are only descriptive and no significance is tested. The coccolithophorid D. anthos and the dinoflagellate Phalacroma spp. were noted as being most dissimilar to all other phytoplankton species with regards to their position in the water column and their response to physico-chemical variables. Finally, the dominance of E. huxleyi in the Mozambique Channel during November/December of 2009 reveals the potential vulnerability of phytoplankton in the channel to ocean acidification.
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Halo, Issufo F. M. "The Mozambique Channel eddies : characteristics and mechanisms of formation." Doctoral thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/6477.
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Includes abstract.Includes bibliographical references.
The model outputs and the satellite data have shown a number of cyclonic and anticyclonic eddies being generated within the Mozambique Channel. The eddies were identified using a newly designed eddy detection algorithm. The algorithm has shown that cyclonic eddies appeared to be more ubiquitous than the anticyclonic and had a single mode sizedistribution. On the other hand, the anticyclonic eddies seemed to have a favorite site for their formation, and have shown a bi-modal size-distribution.
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Pannala, Sreekanth. "On large eddy simulations of reacting two-phase flows." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/11978.
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Zhou, Long. "Mesoscale variability and Lagrangian statistics in the tropical North Atlantic /." View online ; access limited to URI, 2009. http://digitalcommons.uri.edu/dissertations/AAI3401129.
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De, Bruyn Kops Stephen M. "Numerical simulation of non-premixed turbulent combustion /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/7140.
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Lilly, Jonathan M. "Observations of the Labrador Sea eddy field /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/11041.
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Bulhoes, de Morais Cesar Reinert. "On the Evolution of Cyclonic Eddies along the Florida Keys." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_theses/70.
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Cyclonic oceanic vortices (eddies) ranging from ~10 to 150km in diameter that travel along the Florida Keys are investigated. This study employs hydrodynamic parameters from simulations in a high-resolution (~900m horizontally), three-dimensional (26 vertical levels) HYbrid Coordinates Ocean Model regional application to study coastal to offshore interactions along the Florida Keys. These parameters are compared qualitatively to observations from Chlorophyll-a Satellite (SEAWiFs) and HF Radar (WERA). Further, eddy characteristics along the Florida Keys are determined using the Okubo-Weiss parameter combined with Sea-Surface Height fields for the period 2004- 2008. Additionally, their temporal scales are assessed using spectral time-series analysis via Welch?s Fast Fourier Transform and Wavelet Transforms. Some processes that influence eddy evolution along the Florida Keys are presented in the form of case studies. And finally, the relative contribution of mesoscale and submesoscale eddies to the upwelling along the Florida Keys is assessed, supporting the argument that these features contribute to produce water exchanges between the offshore flow and the coastal areas.
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Jaimes, Benjamin. "On the Response to Tropical Cyclones in Mesoscale Oceanic Eddies." Scholarly Repository, 2009. http://scholarlyrepository.miami.edu/oa_dissertations/342.
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Tropical cyclones (TCs) often change intensity as they move over mesoscale oceanic features, as a function of the oceanic mixed layer (OML) thermal response (cooling) to the storm's wind stress. For example, observational evidence indicates that TCs in the Gulf of Mexico rapidly weaken over cyclonic cold core eddies (CCEs) where the cooling response is enhanced, and they rapidly intensify over anticyclonic warm features such as the Loop Current (LC) and Warm Core Eddies (WCEs) where OML cooling is reduced. Understanding this contrasting thermal response has important implications for oceanic feedback to TCs' intensity in forecasting models. Based on numerical experimentation and data acquired during hurricanes Katrina and Rita, this dissertation delineates the contrasting velocity and thermal response to TCs in mesoscale oceanic eddies. Observational evidence and model results indicate that, during the forced stage, the wind-driven horizontal current divergence under the storm's eye is affected by the underlying geostrophic circulation. Upwelling (downwelling) regimes develop when the wind stress vector is with (against) the geostrophic OML velocity vector. During the relaxation stage, background geostrophic circulations modulate vertical dispersion of OML near-inertial energy. The near-inertial velocity response is subsequently shifted toward more sub-inertial frequencies inside WCEs, where rapid vertical dispersion prevents accumulation of kinetic energy in the OML that reduces vertical shears and layer cooling. By contrast, near-inertial oscillations are vertically trapped in OMLs inside CCEs that increases vertical shears and entrainment. Estimates of downward vertical radiation of near-inertial wave energies were significantly stronger in the LC bulge (12.1X10 super -2 W m super -2) compared to that in CCEs (1.8X10 super -2 W m super -2). The rotational and translation properties of the geostrophic eddies have an important impact on the internal wave wake produced by TCs. More near-inertial kinetic energy is horizontally trapped in more rapidly rotating eddies. This response enhances vertical shear development and mixing. Moreover, the upper ocean temperature anomaly and near-inertial oscillations induced by TCs are transported by the westward-propagating geostrophic eddies. From a broader perspective, coupled models must capture oceanic features to reproduce the differentiated TC-induced OML cooling to improve intensity forecasting.
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Roberts, Malcolm. "Investigation of the role of ocean eddies and their parameterization." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389514.
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Arbic, Brian K. "Generation of mid-ocean eddies : the local baroclinic instability hypothesis." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/53047.
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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), 2000.Includes bibliographical references (p. 284-290).
by Brian Kenneth Arbic.
Ph.D.
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Pankratov, Kirill Konstantinovich. "Influence of topography on the dynamics of baroclinic oceanic eddies." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/55020.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1994.Includes bibliographical references (leaves 187-190).
by Kirill Konstantinovich Pankratov.
Ph.D.
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PeÌrez, PeÌrez Edgar. "Heat transport by baroclinic eddies : evaluating eddy parameterizations for numerical models." Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442945.
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Buck, Justin James Henry. "Eddies and instabilities in downslope flows in the Weddell Sea, Antarctica." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507219.
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The Weddell Sea, Antarctica is a significant area of down welling water in the world large scale ocean circulation. When water descends a slope it is subject to instabilities forming mesoscale features such as eddies in the plume. This thesis is a study of the source of the plume of Ice Shelf Water (ISW) that flows down the Filchner Slope and the downslope flow via the Ronne Depression into the cavity beneath the Ronne Ice Shelf. Oceanographic observations and laboratory experiments simulating the influence of an ice shelf on such a flow are used in this study. The oceanographic data sets used for the Filchner slope are mooring records and research cruise data. The study includes the analysis of novel yoyo casts where the plume of ISW is observed for periods of up to 15 hours. Although the flows observed could not be fully classified, the analysis demonstrated the ability of such a data set to observe the plume. The data analysed from the Ronne Ice Front are two mooring records with an emphasis on eddies in the flows. Eddies were observed at the ice front in both moorings with stronger signals observed during the winter freezing season when the water column is unstratified. The question arose as to whether eddies can propagate across the topographic barrier the ice shelf presents and what effect does ambient two layer stratification have? The experiments in the rest of the thesis were conducted to answer this question. The experimental work uses small 1.2 m and a large 14 m diameter rotating table considering the effect that an ice shelf has on the propagation of eddies. In all but one experiment eddies are generated in the flows though a barotropic mechanism initiated through vortex stretching. It is shown that a relatively small change in ice shelf thickness is required to impede the propagation of eddies into the cavity beneath the ice shelf. However, when two-layer stratification is present and the interface is near to the base of the ice shelf eddies appear to propagate into the ice shelf cavity. The results are then compared to observations and it is concluded that the oceanographic implication of this work is that eddies are unlikely to propagate across the barrier that the ice shelf represents. This is even when stratification is present during summer because the vorticity of eddies is weak and the stratification level is located above the ice shelf base.
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Wilson, Christopher. "The role of mesoscale eddies and its representation in numerical models." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484268.
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Tielking, Terrance A. "Wind forcing of eddies and jets in the California current system." Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/23147.
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Williams, R. G. "The influence of air-sea interaction on ocean synoptic-scale eddies." Thesis, University of East Anglia, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.377713.
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Mackenzie, Beverley Anne. "On the primary productivity potential for Lagrangian particles in mesoscale eddies." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.272743.
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Sinha, Bablu. "The influence of mesoscale eddies and topography on southern ocean flow." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239650.
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Fox-Kemper, Baylor 1973. "Eddies and friction : removal of vorticity from the wind-driven gyre." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/39405.
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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), 2003.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 299-310).
Inertial terms dominate the single-gyre ocean model and prevent western-intensification when the viscosity is small. This occurs long before the oceanically-appropriate parameter range. It is demonstrated here that the circulation is controlled if a mechanism for ultimate removal of vorticity exists, even if it is active only in a narrow region near the boundary. Vorticity removal is modeled here as a viscosity enhanced very near the solid boundaries to roughly parameterize missing boundary physics like topographic interaction and three dimensional turbulence over the shelf. This boundary-enhanced viscosity allows western-intensified mean flows even when the inertial boundary width is much wider than the frictional region because eddies flux vorticity from within the interior streamlines to the frictional region for removal. Using boundary-enhanced viscosity, western-intensified calculations are possible with lower interior viscosity than in previous studies. Interesting behaviors result: a boundary-layer balance novel to the model, calculations with promise for eddy param- eterization, eddy-driven gyres rotating opposite the wind, and temporal complexity including basin resonances.
(cont.) I also demonstrate that multiple-gyre calculations have weaker mean circulation than single-gyres with the same viscosity and subtropical forcing. Despite traditional understanding, almost no inter-gyre flux occurs if no-slip boundary conditions are used. The inter-gyre eddy flux is in control only with exactly symmetric gyres and free slip boundaries. Even without the inter-gyre flux, the multiple-gyre circulation is weak because of sinuous instabilities on the jet which are not present in the single-gyre model. These modes efficiently flux vorticity to the boundary and reduce the circulation without an inter-gyre flux, postponing inertial domination to much smaller viscosities.
by Baylor Fix-Kemper.
Ph.D.
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Zhou, Shuyntai. "The role of large-scale atmospheric eddies in the climate equilibrium." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/17291.
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Doddridge, Edward. "Influence of eddies on vertical transport and nutrients in subtropical gyres." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:9ca650eb-fa96-4807-ba78-44b838484334.
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The presence of large-scale Ekman pumping associated with the climatological wind-stress curl is the textbook explanation for low biological activity in the subtropical gyres. Using an idealised model it is shown that Eulerian-mean Ekman pumping may be opposed by an eddy-driven circulation, analogous to the way in which the atmospheric Ferrel cell and the Southern Ocean Deacon cell are opposed by eddy-driven circulations. Potential vorticity fluxes, Lagrangian particle tracking, and depth-density streamfunctions are used to show that, in the model, the rectified effect of eddies acts to largely cancel the Eulerian-mean Ekman downwelling. To distinguish this effect from eddy compensation, it is proposed that the suppression of Eulerian-mean downwelling by eddies be called "eddy cancellation." Eddy cancellation highlights that the thermocline forms a barrier between the surface waters and the abyssal ocean. The presence of this barrier suggests that the nutrient budget of the subtropical mode water and euphotic zone should be considered together. An idealised two-layer axisymmetric model of nutrient concentration in subtropical gyres is developed. This model is used to explore the concept of a unified nutrient budget for the euphotic zone and mode water of subtropical gyres. The steady-state nutrient distribution and fluxes from the idealised model are compared with observations and previous studies. These comparisons show that the solutions of the idealised model are reasonable. Following this validation the sensitivity of the model to changes in parameter values is explored. The model predicts a non-monotonic response to changes in the residual Ekman pumping velocity, with a productivity minimum at 30 m year -1. The model also predicts a positive relationship between primary productivity and mode water thickness. The predicted relationship between primary productivity and mode water thickness is tested using observational datasets, which provide some evidence to support the conclusion that thicker mode waters lead to higher productivity in the oligotrophic gyres.
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Wardle, Richard M. "Representation of eddies in climate models by a potential vorticity flux." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/58540.
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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), February 1999.Includes bibliographical references (p. 170-177).
This thesis addresses the parameterization of the heat and momentum transporting properties of eddy motions for use in three-dimensional, primitive equation, z-coordinate atmosphere and ocean models. Determining the transport characteristics of these eddies is fundamental to understanding their effect on the large-scale ocean circulation and global climate. The approach is to transform the primitive equations to yield the altered 'transformed Eulerian mean' (TEM) equations. The assumption is made that the eddy motions obey quasigeostrophic dynamics while the mean flow obeys the primitive equations. With this assumption, the TEM framework leads to the eddies appearing as one term, which acts as a body force in the momentum equations. This force manifests itself as a flux of potential vorticity (PV) - a quantity that incorporates both eddy momentum and heat transporting properties. Moreover, the dynamic velocities are those of the residual mean circulation, a much more relevant velocity for understanding heat and tracer transport. Closure for the eddy PV flux is achieved through a flux-gradient relationship, which directs the flux down the large scale PV gradient. For zonal flows, care is taken to ensure that the resulting force does not generate any net momentum, acting only to redistribute it. Neglect of relative vorticity fluxes in the PV flux yields the parameterization scheme of Gent and McWilliams. The approach is investigated by comparing a zonally-averaged parameterized model with a three dimensional eddy-resolving calculation of flow in a stress-driven channel. The stress at the upper surface is communicated down the water column to the bottom by eddy form drag. Moreover, lateral eddy momentum fluxes act to strengthen and sharpen the mean flow, transporting eastward momentum up its large scale gradient. Both the vertical momentum transfer and lateral, upgradient momentum transfer by eddies, are captured in the parameterized model. The advantages of this approach are demonstrated in two further zonal cases: 1) the spin-down of a baroclinic zone, and 2) the atmospheric jet stream. The time mean TEM approach and the eddy PV flux closure are explored in the context of an eddy-resolving closed basin flow which breaks the zonal symmetry. Decomposition of eddy PV fluxes into components associated with advective and dissipative effects suggest that the component associated with eddy flux divergence, and therefore forcing of the mean flow, is mainly directed down the large scale gradient and can be parameterized as before. Thus, the approach can be used to capture eddy transport properties for both zonal mean and time mean flows. The PV flux embodies both the eddy heat and momentum fluxes and so presents a more unified picture of their transferring properties. It therefore provides a powerful conceptual and practical framework for representing eddies in numerical models of the atmsophere and ocean.
by Richard M. Wardle.
Ph.D.
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Chien, Yu-Tang. "Change in the Leading Mode of North America's Wintertime Stationary Eddies." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7587.
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Extreme winter weather events in North America have become more frequent and increasingly destructive. This phenomenon was linked to a jet stream pattern that generates abnormally warm conditions in the west and cold conditions in the east, referred to as the North American Winter Dipole. Studies have shown that the Dipole may have amplified and this amplification could be linked to global warming. By analyzing the atmospheric and oceanic data worldwide, the wintertime circulation in the Northern Hemisphere shows signs of a persistent change after the 1980s. In the first part of this study, we examine how the ocean has changed in correspondence to the Dipole and the evolution of the pattern change. In the second part of this study, we use multiple global reanalysis datasets to construct the Dipole index. The result validates the reported Dipole variation during the modern period. We also use the Dipole variance to investigate the Dipole’s behavior in the paleoclimate and future warming conditions. Overall, we sought to better understand how the Dipole pattern evolves and how it may link to the different forcing, as a way to anticipate future change in North America’s winter.
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Badin, Gualtiero. "Are eddies important in the coastal ocean? : a North Sea case study." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440765.
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Hopkins, Alicia A. "Sensitivity of bottom topography on the dynamics and sound speed structure in the Northern Canary Current System." Thesis, Monterey, Calif. : Naval Postgraduate School, 2006. http://bosun.nps.edu/uhtbin/hyperion.exe/06Dec%5FHopkins.pdf.
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Thesis (M.S. in Meterology and Physical Oceanography)--Naval Postgraduate School, December 2006.Thesis Advisor(s): Mary L. Batteen. "December 2006." Includes bibliographical references (p. 101-105). Also available in print.
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Combes, Vincent Emmanuel. "Intrinsic and Forced Interannual Variability of the Gulf of Alaska Mesoscale Circulation." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14532.
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The response of the Gulf of Alaska (GOA) circulation to large-scale North Pacific climate variability is explored using three high resolution (15 km) regional ocean model ensembles over the period 1950-2004. On interannual and decadal timescales the mean circulation is strongly modulated by changes in the large scale climate forcing associated with PDO and ENSO. Intensification of the model gyre scale circulation occurs after the 1976-1977 climate shift, as well as during 1965-1970 and 1993-1995. From the model dynamical budgets we find that when the GOA experiences stronger southeasterly winds, typical during the positive phase of the PDO and ENSO, there is net large-scale Ekman convergence in the central and eastern coastal boundary. The geostrophic adjustment to higher sea surface height (SSH) and lower isopycnals lead to stronger cyclonic gyre scale circulation. The opposite situation occurs during stronger northwesterly winds (negative phase of the PDO).
Along the eastern basin, interannual changes in the surface winds also modulate the seasonal development of high amplitude anticyclonic eddies (e.g. Hada and Sitka eddies). Large interannual eddy events during winter-spring, are phase-locked with the seasonal cycle. The initial eddy dynamics are consistent with a quasi-linear Rossby wave response to positive SSH anomalies forced by stronger downwelling favorable winds (e.g. southwesterly during El Nio). However, because of the fast growth rate of baroclinic instability and the geographical focusing associated with the coastal geometry, most of the perturbation energy in the Rossby wave is locally trapped until converted into large scale nonlinear coherent eddies. Coastally trapped waves of tropical origin may also contribute to positive SSH anomalies that lead to higher amplitude eddies. However, their presence does not appear essential. The model ensembles, which do not include the effects of equatorial coastally trapped waves, capture the large Hada and Sitka eddy events observed during 1982 and 1997 and explain most of the variance of tidal gauges along the GOA coast.
In the western basin, interannual eddy variability located south of the Alaskan Stream is not correlated with large scale forcing and appears to be intrinsic. A comparison of the three model ensembles forced by NCEP winds and a multi-century-long integration forced only with the seasonal cycle, shows that the internal variability alone explains most of the eddy variance. The asymmetry between the eddy forced regime in the eastern basin, and the intrinsic regime in the western basin, has important implications for predicting the GOA response to climate change. Eastern boundary eddies transport important biogeochemical quantities such as iron, oxygen and chlorophyll-a into the gyre interior, therefore having potential upscale effects on the GOA high-nutrient-low-chlorophyll region.
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Eden, Bethany Rose. "Zooplankton Community Structure in a Cyclonic and Mode-Water Eddy in the Sargasso Sea." W&M ScholarWorks, 2008. http://www.vims.edu/library/Theses/Eden08.pdf.
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Baker-Yeboah, Sheekela. "Sea surface height variability and the structure of eddies in the South Atlantic Cape Basin /." View online ; access limited to URI, 2008. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3314440.
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Chen, Shuiming. "Vertical structure of mesoscale ocean currents in the Indian Ocean observation, numerical modeling and theory /." Thesis, University of Hawaii at Manoa, 2003. http://proquest.umi.com/pqdweb?index=0&did=765960941&SrchMode=2&sid=8&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1209408688&clientId=23440.
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Yin, Jeffrey Hiapo. "The peculiar behavior of baroclinic waves during the midwinter suppression of the Pacific storm track /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/10043.
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Zidikheri, Meelis Juma. "Dynamical subgrid-scale parameterizations for quasigeostrophic flows using direct numerical simulations /." View thesis entry in Australian Digital Theses, 2007. http://thesis.anu.edu.au/public/adt-ANU20090108.112027/index.html.
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Lo, Piccolo Anna. "Arctic ocean submesoscale brine driven eddies: modeling of a sea ice edge front." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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Characteristic features of the wintertime Arctic Ocean are narrow and elongated fractures in the sea ice cover, up to hundreds of kilometers long and up to tens of kilometers wide, called leads. Leads expose the ocean to the cold atmosphere, establishing air-sea heat fluxes which freeze the oceanic surface. During new sea ice formation, dense and salt-enriched plumes of brine are rejected into the oceanic mixed-layer. Due to brine rejection, lateral density gradients appear at sea ice edges, creating fronts. Fronts store potential energy and are subjected to gravitational overturning. The effect of Earth's rotation prevents the complete slumping establishing along sea sea ice edge currents in a geostrophic balance state, known as geostrophic adjustment, leaving the isopycnals tilted. Baroclinic instabilities develop and grow into submesoscale eddies - typical vortical coherent structures of the oceanic mixed-layer. Transferring momentum and tracer properties laterally, submesoscale eddies are the leading order process of mixed-layer restratification. Current global climate models can not resolve this small scale turbulence and Arctic Ocean observations are limited due to the presence of sea ice. High resolution numerical models are therefore a powerful tool for investigating these unknown processes. In this work, idealized high resolution model experiments are setup in order to study the wintertime refreezing of an open ocean area near a sea ice edge. The results confirm that submesoscale eddies enhance the mixed-layer restratification subtracting energy from the mean flow and increasing the turbulent kinetic energy. Through the study of lateral density transfer scaling rate, a departure from the deformation radius emerges in geostrophic adjustment experiments and more strongly under ageostrophy predominance. The presence of an ageostrophic diffusion process can explain the frontal region widening.
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Yu, Wei. "On the interactions between the atmospheric seasonal mean flow and the transient eddies." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60457.
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Our study is concerned with the winter climatology over the Northern Hemisphere for the years 1980 to 1986.The local E-P flux divergence is divided into barotropic and baroclinic components. The 300 mb level is chosen to represent the upper troposphere. The three dominant convergence centres of the baroclinic component are found on the east coast of Asia, near the eastern Pacific and on the east coast of North America. In most areas the barotropic component of the eddy forcing accelerates the mean flow. Near the dateline the barotropic and baroclinic components of the eddy forcing tend to enhance each other, while on the east coast of North American the barotropic and baroclinic components partially cancel each other.
The three-dimensional structure of some general circulation statistics are discussed, and the results are compared with those of earlier studies.
The possible link between the interannual variation of the seasonal mean flow and the transient eddies forcing is discussed. The results show that no obvious correlation exists in our data set, so that no firm conclusions can be reached.
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de, Giovanetti Matteo. "Attached eddies in wall-bounded turbulent flows : streak instability and skin-friction generation." Thesis, Imperial College London, 2018. http://hdl.handle.net/10044/1/63818.
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The goal of this study is to answer some lingering questions that pertain the nature of wall-bounded turbulent flows. Building on the ‘attached-eddy’ hypothesis first proposed by A.A. Townsend, the main aim is to better understand the mechanisms governing their behaviour. In order to do so, several numerical experiments are performed in a turbulent channel flow. First, we seek for a better description of the mechanism behind the generation of the vortical structures: a body forcing is introduced in the flow to drive an amplified streak, and this process is carried out for several different streaks, ranging from the logarithmic to the outer region. All streaks are shown to undergo a sinuous-type instability; furthermore, they trigger the appearance of cross-streamwise structures, the streamwise wavelength scale of which is observed to be proportional to the spanwise spacing of the amplified streak. Application of dynamic mode decomposition reveals that the amplified streak can be considered the seeding mechanism for these vortical structures. Furthermore, the contribution of attached eddies to skin-friction drag is studied at relatively large Reynolds numbers. It is found that the outer-layer structures are responsible for a significant amount of skin-friction, but their removal does not result in comparable savings. Conversely, the self-similar structures populating the logarithmic layer are shown to generate a substantial amount of skin friction, and their contribution appears to increase with the Reynolds number. This outcome can explain the reduction in effectiveness of many drag-reducing devices, and is potentially useful to design novel techniques for flow control.
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Brett, Genevieve Elizabeth. "Chaotic advection, mixing, and property exchange in three-dimensional ocean eddies and gyres." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/117913.
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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), 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 259-268).
This work investigates how a Lagrangian perspective applies to models of two oceanographic flows: an overturning submesoscale eddy and the Western Alboran Gyre. In the first case, I focus on the importance of diffusion as compared to chaotic advection for tracers in this system. Three methods are used to quantify the relative contributions: scaling arguments including a Lagrangian Batchelor scale, statistical analysis of ensembles of trajectories, and Nakamura effective diffusivity from numerical simulations of dye release. Through these complementary methods, I find that chaotic advection dominates over turbulent diffusion in the widest chaotic regions, which always occur near the center and outer rim of the cylinder and sometimes occur in interior regions for Ekman numbers near 0.01. In thin chaotic regions, diffusion is at least as important as chaotic advection. From this analysis, it is clear that identified Lagrangian coherent structures will be barriers to transport for long times if they are much larger than the Batchelor scale. The second case is a model of the Western Alboran Gyre with realistic forcing and bathymetry. I examine its transport properties from both an Eulerian and Lagrangian perspective. I find that advection is most often the dominant term in Eulerian budgets for volume, salt, and heat in the gyre, with diffusion and surface fluxes playing a smaller role. In the vorticity budget, advection is as large as the effects of wind and viscous diffusion, but not dominant. For the Lagrangian analysis, I construct a moving gyre boundary from segments of the stable and unstable manifolds emanating from two persistent hyperbolic trajectories on the coast at the eastern and western extent of the gyre. These manifolds are computed on several isopycnals and stacked vertically to construct a three-dimensional Lagrangian gyre boundary. The regions these manifolds cover is the stirring region, where there is a path for water to reach the gyre. On timescales of days to weeks, water from the Atlantic Jet and the northern coast can enter the outer parts of the gyre, but there is a core region in the interior that is separate. Using a gate, I calculate the continuous advective transport across the Lagrangian boundary in three dimensions for the first time. A Lagrangian volume budget is calculated, and challenges in its closure are described. Lagrangian and Eulerian advective transports are found to be of similar magnitudes.
by Genevieve Elizabeth Brett.
Ph. D.