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Sharifuzzaman, MD. "Dynamics of Crystalline Gravity Currents". Thesis, Griffith University, 2018. http://hdl.handle.net/10072/381374.
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Gravity currents, which are also known as density currents, are established when one fluid flows into another of different density, and the density difference between the two drives the flow. They are widespread and vital phenomena that occur within numerous natural systems (Lemckert and Imberger, 1993a, b; Lemckert et al., 2002; Yu et al., 2013; Zigic et al., 2002).
While the majority of commonly occurring gravity currents have received significant attention by researchers, crystalline gravity currents have not been studied extensively yet, and there is very little fundamental knowledge about their behavior. Crystalline and particle-driven gravity currents are suspensions of dense particles that spread into an ambient fluid due to the difference between the density of suspension and that of the ambient fluid (Sparks et al., 1997; Simpson, 1997). Studies have been conducted in laboratories analyzing gravity currents mainly on lock exchange phenomenon (Huppert and Simpson, 1980; Hallworth et al. 1996; Lemckert et al., 2002; Rottman and Simpson, 1983; Shin et al., 2004) and continuous inflow phenomenon (Ellison and Turner, 1959; Garcia, 1993; Maxworthy, 1983; Middleton, 1966b; Zhang et al., 2008). In Lock exchange mechanism, two fluids of varying density are kept separate by a lock gate. The fluid with higher density is known as the lock fluid and it has significantly lower volume than the second fluid. When the lock gate is removed, gravity current forms because of the density difference between the fluids. During the evolution of the current, the particles continually deposit or dissolve, thus reducing the excess density of suspension and the driving buoyancy force (e. g. during the late stages of turbidity currents, Parker et al., 1986). While the non-dissolving kind (sediment-laden) is well studied by many researchers (Fragoso et al., 2013; Garcia, 1994; Hallworth et al., 1996; Kuenen, 1937; Parker et al., 1986; Simpson and Britter, 1979; Shin et al., 2004;), the crystalline gravity currents are not being looked at. The focus of this study was on these currents produced by lock release inflow of highly saline solution with suspended salt crystals to understand their behavior, and the impact they may have on the receiving environment. The results were then compared with those of unsaturated gravity currents under the same experimental conditions. Data were also extracted from the literature for sediment-laden lock release gravity currents under similar experimental conditions and compared with the findings of this study focusing on the self-similar phase.
The outcomes of this experimental study showed that dynamics of crystalline gravity currents are entirely different from those of unsaturated and sediment-laden gravity currents. The temporal change in the driving buoyancy affects its characteristics. The research and outcomes of this study will assist in providing first-hand knowledge of the progress of gravity currents with initially suspended salt crystals in lock release condition into a receiving environment.Thesis (Masters)
Master of Philosophy (MPhil)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text
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Kuehl, Joseph J. "On the dynamics of oceanic gap-traversing boundary currents /". View online ; access limited to URI, 2009. http://digitalcommons.uri.edu/dissertations/AAI3401123.
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Edwards, Deborah Anne. "Turbidity currents : dynamics, deposits and reversals". Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293760.
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Le, Bras Isabela Astiz. "Dynamics of North Atlantic western boundary currents". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/109056.
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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), 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 163-174).
The Gulf Stream and Deep Western Boundary Current (DWBC) shape the distribution of heat and carbon in the North Atlantic, with consequences for global climate. This thesis employs a combination of theory, observations and models to probe the dynamics of these two western boundary currents. First, to diagnose the dynamical balance of the Gulf Stream, a depth-averaged vorticity budget framework is developed. This framework is applied to observations and a state estimate in the subtropical North Atlantic. Budget terms indicate a primary balance of vorticity between wind stress forcing and dissipation, and that the Gulf Stream has a significant inertial component. The next chapter weighs in on an ongoing debate over how the deep ocean is filled with water from high latitude sources. Measurements of the DWBC at Line W, on the continental slope southeast of New England, reveal water mass changes that are consistent with changes in the Labrador Sea, one of the sources of deep water thousands of kilometers upstream. Coherent patterns of change are also found along the path of the DWBC. These changes are consistent with an advective-diffusive model, which is used to quantify transit time distributions between the Labrador Sea and Line W. Advection and stirring are both found to play leading order roles in the propagation of water mass anomalies in the DWBC. The final study brings the two currents together in a quasi-geostrophic process model, focusing on the interaction between the Gulf Stream's northern recirculation gyre and the continental slope along which the DWBC travels. We demonstrate that the continental slope restricts the extent of the recirculation gyre and alters its forcing mechanisms. The recirculation gyre can also merge with the DWBC at depth, and its adjustment is associated with eddy fluxes that stir the DWBC with the interior. This thesis provides a quantitative description of the structure of the overturning circulation in the western North Atlantic, which is an important step towards understanding its role in the climate system.
by Isabela Astiz Le Bras.
Ph. D.
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Thorpe, Antony. "Sediment transport and bedform dynamics in rip currents". Thesis, University of Plymouth, 2016. http://hdl.handle.net/10026.1/6558.
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Simultaneous in-situ measurements of waves, currents, water depth, suspended sediment concentrations and bed profiles were made in a rip channel on Perranporth Beach, Cornwall, UK. Perranporth is a high energy beach (annual offshore Hs = 1.6 m) which is macro-tidal (mean spring range = 6.3 m) and the grain size is medium sand (D50 = 0.28 – 0.34 mm). It can be classified as a low tide bar – rip beach and exhibits a relatively flat inter-tidal zone with pronounced rhythmic low tide bar - rip morphology. Data were collected over two field campaigns, totalling 14 tidal cycles and including 27 occurrences of rip currents, in a range of offshore wave heights (Hs = 0.5 – 3 m). The in-situ measurements were supplemented with morphological beach surveys. Sediment samples were taken for grain size analysis. The rip current was found to be tidally modulated. The strongest rip flow (0.7 m/s) occurred at mid to low tide, when waves were breaking on the adjacent bar. Rip flow persisted when the bar had dried out at the lowest tidal elevations. The rip was observed to pulse at a very low frequency (VLF) with a period of 15 - 20 minutes, which was shown to be influenced by wave breaking on the adjacent bar. The rip was completely in-active at high tide. Bedforms were ubiquitous in the rip channel and occurred at all stages of the tide. Visual observations found bedforms to be orientated shore parallel. When the rip was active, mean bedform length and height was 1.45 m and 0.06 m respectively. The size and position of the bedforms in the nearshore suggested that they were best classified as megaripples. When the rip was not active, the mean bedform length and height was 1.09 m and 0.06 m respectively. In rip conditions, with typical mean offshore flow rates of > 0.3 m/s, the bedforms migrated in an offshore direction at a mean rate of 0.16 cm/min and a maximum rate of 4.6 cm/min. The associated mean bedform sediment transport rate was 0.0020 kg/m/s, with a maximum rate of 0.054 kg/m/s. In the rip, migration rates were correlated with offshore directed mean flow strength. In non-rip conditions, bedform migration was onshore directed with a mean rate of 0.09 cm/min and a maximum rate of = 2.2 cm/min. The associated mean bedform transport rate was 0.0015 kg/m/s, with a maximum rate of = 0.041 kg/m/s. The onshore bedform transport was correlated with incident wave skewness, and was weakly correlated with orbital velocity. Over a tidal cycle, the offshore directed bedform transport was only marginally larger in rip currents than when it was when onshore directed in non-rip conditions. Sediment suspension in the rip current was shown to be dependent on the presence of waves. Suspended sediment transport was dominated by the mean flux. The mean flux contributed > 70% of total suspended transport on 19 out of the 27 observed rip current occurrences. The net contribution of the oscillatory flux was small compared to the mean flux. Within the oscillatory component, a frequency domain partitioning routine showed that the VLF motion was an important mechanism for driving offshore directed sediment transport. This was balanced by onshore directed sediment transport at incident wave frequency of a similar magnitude. Depth integration showed that the mean total suspended sediment transport was in the range of 0.03 kg/m/s to 0.08 kg/m/s. At high tide, when the rip was inactive suspended sediment transport rates were minimal compared to when the rip was active. Bedform transport was (on average) 6% of the total suspended sediment transport in a rip current. The new results presented here show that rip currents make an important contribution to offshore directed sediment transport. The magnitudes of transport indicate that future improvements to morphology change models should include rip driven offshore sediment transport.
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Cordoba, Gustavo. "Dilute particle-laden currents : dynamics and deposit patterns". Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495639.
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A numerical model based on the full Navier-Stokes equations is developed to study the dynamics and deposit patterns of turbidity currents. The equation system is simplified using the dilute flow condition which allows one set of momentum equations. The model allows to simulate multiparticle flows in an ambient of pure or sea-water. The solution of the mathematical model is done extending the Characteristic-Based-Split (CBS) Finite Element algorithm to particle-laden flows. The algorithm is implemented by developing a computer program coded in Fortran 90. Additionally, a Box model based on mass balance is developed, which allows to account for the sedimentation, multiple particles and slope changes. Two dimensional and radial flows can be modelled using the proposed Box model just by changing the initial and boundary conditions. The confidence of both the Navier-Stokes based model and the mass-balance based Box model are successfully tested using laboratory experimental data.
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Barrass, Timothy Adam. "Dynamics and sedimentation from axisymmetric, polydisperse gravity currents". Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.288282.
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Girton, James Bannister. "Dynamics of transport and variability in the Denmark Strait overflow /". Thesis, Connect to this title online; UW restricted, 2001. http://hdl.handle.net/1773/11023.
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Gregorio, Sandy O. "Investigation on the dynamics of gravity-driven coastal currents". Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/47656/.
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Numerical simulations of buoyant, gravity-driven coastal plumes are summarized and compared to the inviscid geostrophic theory of Thomas & Linden (2007) and to laboratory studies for plumes owing along a vertical-wall coastline (those of Thomas & Linden (2007) and additional experiments performed at Warwick University). In addition, results of two new laboratory studies with different scales for plumes owing along a more realistic inclined-wall coastline are presented and compared to an extended theoretical model from the geostrophic theory of Thomas & Linden (2007). The theoretical and experimental results for plumes flowing along inclined-wall coastlines are compared to the inclined-wall experimental studies of Avicola & Huq (2002), Whitehead & Chapman (1986) and Lentz & Helfrich (2002), to the inclined-wall scaling theory of Lentz & Helfrich (2002), and to oceanic observations. The lengths, widths and velocities of the buoyant gravity currents are studied. Agreement between the laboratory and numerical experiments, and the geostrophic theories for both vertical-wall and inclined-wall studies is found to depend mainly on one non-dimensional parameter which characterizes the strength of horizontal viscous forces (the horizontal Ekman number). The best agreement between the experiments and the geostrophic theories is found for plumes with low viscous forces. At large values of the horizontal Ekman number, laboratory and numerical experiments depart more significantly from theory (e.g., in the plume propagation velocity). At very low values of the horizontal Ekman number (obtained in the large-scale inclined-wall experimental study only), departures between experiments and theory are observed as well. Agreement between experiments and theory is also found to depend on the steepness of the plumes isopycnal interface for the vertical-wall study, and on the ratio between the isopycnal and coastline slopes for the inclined-wall study.
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Meuleners, Michael Joseph. "A numerical study of the mesoscale eddy dynamics of the Leeuwin Current system /". Connect to this title, 2005. http://theses.library.uwa.edu.au/adt-WU2007.0134.
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Restrepo, Juan M., e Shankar Venkataramani. "Stochastic longshore current dynamics". ELSEVIER SCI LTD, 2016. http://hdl.handle.net/10150/621938.
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We develop a stochastic parametrization, based on a 'simple' deterministic model for the dynamics of steady longshore currents, that produces ensembles that are statistically consistent with field observations of these currents. Unlike deterministic models, stochastic parameterization incorporates randomness and hence can only match the observations in a statistical sense. Unlike statistical emulators, in which the model is tuned to the statistical structure of the observation, stochastic parametrization are not directly tuned to match the statistics of the observations. Rather, stochastic parameterization combines deterministic, i.e physics based models with stochastic models for the "missing physics" to create hybrid models, that are stochastic, but yet can be used for making predictions, especially in the context of data assimilation. We introduce a novel measure of the utility of stochastic models of complex processes, that we call consistency of sensitivity. A model with poor consistency of sensitivity requires a great deal of tuning of parameters and has a very narrow range of realistic parameters leading to outcomes consistent with a reasonable spectrum of physical outcomes. We apply this metric to our stochastic parametrization and show that, the loss of certainty inherent in model due to its stochastic nature is offset by the model's resulting consistency of sensitivity. In particular, the stochastic model still retains the forward sensitivity of the deterministic model and hence respects important structural/physical constraints, yet has a broader range of parameters capable of producing outcomes consistent with the field data used in evaluating the model. This leads to an expanded range of model applicability. We show, in the context of data assimilation, the stochastic parametrization of longshore currents achieves good results in capturing the statistics of observation that were not used in tuning the model.
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So, Damon Wai Kwan. "The dynamics of two-dimensional propagating jumps and density currents". Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38165.
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Springer, Scott R. "Dynamics of western boundary currents in simple models of low-latitude circulations /". Thesis, Connect to this title online; UW restricted, 1994. http://hdl.handle.net/1773/11010.
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Guthrie, Vanessa M. "Dynamics of eastern boundary currents and their effects on sound speed structure". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FGuthrie.pdf.
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Thesis (M.S. in Physcial Oceanography)--Naval Postgraduate School, June 2006.Thesis Advisor(s): Mary L. Batteen, John A. Colosi. "June 2006." Includes bibliographical references (p. 69-73). Also available in print.
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Combes, Vincent. "Upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34814.
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The upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary is explored using a high resolution ocean model for the last 60 years. Three ocean circulations have been modeled. From North to South, we investigate the dynamics of the Gulf of Alaska (GOA), the California Current System (CCS) and the Humboldt Current System (HCS, also known as the Peru-Chile Current System). The statistics of coastal waters transport are computed using a model passive tracer, which is continuously released at the coast. By looking at the passive tracer concentration distribution, we find that the Pacific Decadal Oscillation modulates the coastal variability of the GOA, the North Pacific Gyre Oscillation controls the upwelling of the CCS, while the El-Niño Southern Oscillation affects the upwelling of Peru and Chile mainly through coastally trapped Kelvin waves. Results also emphasize the key role of the mesoscale eddies in the offshore transport of coastal waters masses. The passive tracer experiments, performed in this study in the GOA, CCS, and HCS, therefore could provide a dynamical framework to understand the dynamics of the upwelling/downwelling and offshore transport of nutrient rich coastal water and to interpret how it responds to atmospheric forcing. This also could reinforce our interpretation (and therefore predictions) in the changes in vertical and offshore advection of other important biogeochemical quantities, essential in understanding ecosystem variability.
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Benage, Mary Catherine. "The thermal evolution and dynamics of pyroclasts and pyroclastic density currents". Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53962.
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The thermal evolution of pyroclastic density currents (PDCs) is the result of entrainment of ambient air, particle concentration, and initial eruptive temperature, which all impact PDC dynamics and their hazards, such as runout distance. The associated hazards and opaqueness of PDCs make it impossible for in-situ entrainment efficiencies or concentration measurements that would provide critical information on the thermal evolution and physical processes of PDCs. The thermal evolution of explosive eruptive events such as volcanic plumes and pyroclastic density currents (PDCs) is reflected in the textures of the material they deposit. A multiscale model is developed to evaluate how the rinds of breadcrust bombs can be used as a unique thermometer to examine the thermal evolution of PDCs. The multiscale, integrated model examines how bubble growth, pyroclast cooling, and dynamics of PDC and projectile pyroclasts form unique pyroclast morphology. Rind development is examined as a function of transport regime (PDC and projectile), transport properties (initial current temperature and current density), and pyroclast properties (initial water content and radius). The model reveals that: 1) rinds of projectile pyroclasts are in general thicker and less vesicular than those of PDC pyroclasts; 2) as the initial current temperature decreases due to initial air entrainment, the rinds on PDC pyroclasts progressively increase in thickness; and 3) rind thickness increases with decreasing water concentration and decreasing clast radius. Therefore, the modeled pyroclast’s morphology is dependent not only on initial water concentration but also on the cooling rate, which is determined by the transport regime.
The developed secondary thermal proxy is then applied to the 2006 PDCs from the Tungurahua eruption to constrain the entrainment efficiency and thermal evolution of PDCs. A three-dimensional multiphase Eulerian-Eulerian-Lagrangian (EEL) model is coupled to topography and field data such as paleomagnetic data and rind thicknesses of collected pyroclasts to study the entrainment efficiency and thus the thermal history of PDCs at Tungurahua volcano, Ecuador. The modeled results that are constrained with observations and thermal proxies demonstrate that 1) efficient entrainment of air to the upper portion of the current allows for rapid cooling, 2) the channelized pyroclastic density currents may have developed a stable bed load region that was inefficient at cooling and 3) the PDCs had temperatures of 600-800K in the bed load region but the upper portion of the currents cooled down to ambient temperatures. The results have shown that PDCs can be heterogeneous in particle concentration, temperature, and dynamics and match observations of PDCs down a volcano and the thermal proxies. Lastly, the entrainment efficiencies of PDCs increases with increasing PDC temperature and entrainment varies spatially and temporally. Therefore, the assumption of a well-mixed current with a single entrainment coefficient cannot fully solve the thermal evolution and dynamics of the PDC.
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Hahn, Christian. "Magnetization dynamics and pure spin currents in YIG/normal-metal systems". Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066657.
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Le domaine de recherche de la spintronique vise a concevoir des dispositifs électroniques misant sur le degré de libre de spin pour transporter de l'information. An d'intégrer ces courants de spin dans des dispositifs électroniques, il est particulièrement intéressant d'étudier l'inter-conversion d'un pur courant de spin en un courant de charge par l'effet Hall de spin, ainsi que le transfert de moment angulaire entre les électrons de conduction d'un métal normal (NM) et l'aimantation d'un ferromagnétique (FM) (couple de transfert de spin / pompage de spin). An de mieux comprendre ces différentes interaction, cette thèse se concentre sur l'étude du système hybride constitué de la juxtaposition d'un ferrimagnétique isolant, le grenat d'yttrium fer (YIG), et d'un métal normal _a fort couplage spin-orbite (Pt ou Ta), nécessaire pour bénéficier de la polarisation en spin de l'interface par un courant électrique dans le plan. Nous avons étudié le pompage de spin et la magnétorésistance produite par l'effet Hall de spin a l'interface entre des bicouches de YIG j Pt et YIG j Ta, et ceci sur des lms étendus de YIG de 200 nm d'épaisseur, produits par épitaxie en phase liquide. Nous observons que la tension électrique, produite par l'effet Hall de spin inverse, change de signe entre du Pt et du Ta confirmant ainsi l'inversion des signes de l'angle de Hall entre ces deux matériaux. En outre, en mesurant la variation de la tension de Hall inverse en fonction de l'épaisseur de la couche de Ta, nous avons réussi à borner la longueur de diffusion de spin dans le Ta. Tant le YIG j Pt et le YIG j Ta affiche une variation semblable de la magnétorésistance a effet Hall de spin en fonction de l'orientation du champ magnétique. Pour étudier l'inuence interfaciale du pompage de spin…Spintronics aims at designing electronic devices which capitalize on the spin degree of freedom to transport information using spin currents. In order to incorporate spin currents intoelectronic devices, it is particularly interesting to study the interconversion from a spin current, the motion of spin angular momentum, to a charge current (Spin Hall Effect) as well as the transfer of spin angular momentum between the conduction electrons of a normal metal (NM) and the magnetization of a ferromagnet (FM) (Spin Transfer Torque/Spin Pumping). To investigate the interplay of those effects this thesis studies hybrid systems of the ferromagnetic insulator Yttrium Iron Garnet and normal metals with large spin-orbit coupling, a prerequisite for spin Hall e_ect. We study spin pumping and spin hall magnetoresistance in YIGjPt and YIGjTa bi-layers using extended _lms of 200 nm thick YIG, grown by liquid phase epitaxy. The inverse spin Hall voltages in Pt and Ta confirm the opposite signs of spin Hall angles in these two materials. Moreover, from the dependence of the inverse spin Hall voltage on the Ta thickness, we constrain the spin di_usion length in Ta. Both the YIGjPt and YIGjTa systems display a similar variation of resistance upon magnetic eld orientation, the spin Hall magnetoresistance. To study the inuence of interfacial spin pumping and a possible reverse e_ect, it is desirable to work with thin _lm thicknesses. A high quality 20 nm thick YIG _lm was grown by pulsed laser deposition, showing a damping similar to that of bulk YIG. We use nano-lithography to pattern series of YIG(20nm) and YIG(20nm)jPt(13nm) discs with diameters between 300 and 700 nm. The ferromagnetic resonance (FMR) spectra of the individual sub-micron sized samples are recorded through magnetic resonance force microscopy. . Passing dc-current through micron sized YIGjPt disks reveal a variation of the FMR linewidth consistent with the geometry and amplitude of the expected SHE transfer torque. In the absence of exciting microwave _elds, a variation in the magnetization is detected when the dc-current reaches the expected threshold for auto oscillations
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Batt, Rachel Louise. "The influence of bed roughness on the dynamics of gravity currents". Thesis, University of Leeds, 2008. http://etheses.whiterose.ac.uk/11282/.
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To date the influence of bed roughness onl the propagation and dynamics of gravity currents has been largely neglected. A new physical modelling dataset has been compiled, which details the fundamental affects of several bed roughnesses on lock-release gravity currents. Five bed configurations were chosen encompassing 'grain' and 'form' type elements at a range of spacings. 1%, 5% and 10% initial density excesses were studied and the effect of removing the buoyant ambient fluid between the elements examined. Observations due to changing the current depth relative to the element height were also made. Ultrasonic Doppler velocimetry profiling (UDVP) and video capture techniques were used to analyse stream wise and vertical velocity structures and the affects on the front speed and distance travelled by the current. A 10 depth-averaged model solves modified 2-layer shallow water equations using the method of characteristics to obtain temporal velocity and depth evolution for a current under the influence of a general roughness quantity. 2D and 3D depth-resolved CFD simulations use the commercial software FLUENT to solve the RANS equations and transport of a scalar for the dense current with the RNG k - € turbulence model. The CFD predictions were well validated by the new experimental dataset and provide supplementary predictions of concentration, lateral motion and activity in the vicinity of the roughness elements. Comparison of 20 and 30 models resulted in the conclusion that the 3D model is vital for accurate simulation of internal dynamics of gravity current propagation over beam type bed roughness. In general general, the distance that the front travels decreases with any bed roughness present. This reduction increases with element spacing. The stream wise mean velocity profiles show a reduced velocity maximum further from the bed. Decreased entrainment results from breakdown of larger billows. Also observed is a thicker current, a rounder profile and a shorter, diluted head. Areas of increased vertical motion within the current. associated with decreased horizontal motion are observed, indicative of ejections of ambient fluid from between the elements. The presence of this fluid is found to contribute to ~ 50% of the current retardation. There are also similarities with the effects of bed roughness in open channel and pipe flows, most notably there is a critical element spacing (11'/ kr ~ 7) where the effects of roughness are greatest (where w is element spacing and kr is element height). The experimental and numerical results demonstrate that the application of existing models that rely on experimental validation with smooth beds to situations where a rough boundary is present may lead to significant errors.
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Berry, William Alexander. "A hydrodynamic characterization of tidal ecosystems with respect to predation". Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31848.
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Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.Committee Chair: Webster, Don; Committee Member: Sturm, Terry; Committee Member: Weissburg, Marc. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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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.
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Hanson, Christine Elizabeth. "Oceanographic forcing of phytoplankton dynamics in the coastal eastern Indian Ocean". University of Western Australia. Centre for Water Research, 2004. http://theses.library.uwa.edu.au/adt-WU2005.0033.
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[Truncated abstract] This work was the first large-scale biological oceanographic study to be undertaken in the coastal eastern Indian Ocean adjacent to Western Australia, and covered both northwest (Exmouth Peninsula to the Abrolhos Islands) and southwest (Cape Naturaliste to Cape Leeuwin) regions. The study area was dominated by the Leeuwin Current (LC), an anomalous eastern boundary current that transports tropical water poleward and prevents deep nutrients from reaching the surface by creating large-scale downwelling. Indeed, LC and offshore waters were consistently associated with low nitrate concentrations and low phytoplankton biomass and production (< 200 mg C m-2 d-1). However, the physical forcing of the LC was offset, during the summer months, by upwelling associated with wind-driven inshore countercurrents (Ningaloo and Capes Currents), which provided a mechanism to access high nutrient concentrations normally confined to the base of the LC. ... Limited seasonal investigations off the Capes region of southwestern Australia showed that the winter production scenario can be very different than summer conditions, with strong Leeuwin Current flow that meanders onto the continental shelf and entrains seasonally nutrient-enriched shelf waters. However, production in the LC was still low (≤450 mg C m-2 d-1) due to light limitation resulting from both increased light attenuation and reduced surface irradiance characteristic of the winter months. This investigation provides fundamental knowledge on physical-biological coupling off Western Australia, with implications for fisheries management in view of seasonal and inter-annual variability in the strength of both the Leeuwin Current and inshore countercurrents.
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Melato, Lebohang Innocentia. "Characterization of the Carbonate System across the Agulhas and Agulhas Return Currents". Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15745.
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In this study, we investigate the role that the solubility and biological pumps have on CO₂ variability across the Agulhas Current system ( Agulhas Current and the Agulhas Return Current). The Agulhas Current system transports heat and salt from the Indian Ocean into the South Atlantic Ocean via the Agulhas leakage, which influences the Atlantic Meridional Overturning Circulation (AMOC). This study presents for the first time a characterization of the role the Agulhas Current system (Agulhas and Agulhas Return Currents) has on the uptake of anthropogenic CO₂. Fugacity of carbon dioxide (fCO₂ ) values were obtained from a ship-based underway pCO₂ (partial pressure of carbon dioxide) system and the air-sea CO₂ fluxes were computed using 6-hourly wind speeds from the NOAA Blended Sea Winds. An experiment was conducted during the Crossroads scientific monitoring line in May 2013, where surface dissolved inorganic carbon, total alkalinity and CO₂ flux were compared between the Agulhas and Agulhas Return Currents and the region directly south over the Agulhas Plateau. Our findings highlighted that the solubility and biological pumps played minimal to no role in the drawdown of carbon across the sub-Tropical zone and the Agulhas Current system (Agulhas and Agulhas Return Currents), due to opposing effect between chlorophyll and temperature on pCO₂ that explained why although there was carbon drawdown by primary production in the Agulhas and Agulhas Return Current regions, this does not play a role in enhancing the air-sea exchange of CO₂. The solubility pump was responsible for CO₂ in the sub-Antarctic zone. The biological and solubility pumps were responsible for CO₂ sink in the Agulhas Plateau eddy. The highest CO₂ flux in the study was observed in the Agulhas Plateau eddy at a flux value of -8.12 mmolC.m-².day-¹ due to the cooler mean sea surface temperature of ~16.5 °C. This is the first time that such as study has been undertaken and aims to provide a better understanding of the role of Western Boundary Currents such as the Agulhas Current has in the uptake of CO₂.
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Chumbinho, Rogřio Paulo Antunes. "Kinematics and dynamics of a cyclonic eddy off Pt. Arena, California /". Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA298587.
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Dissertation (Ph. D. in Physical Oceanography) Naval Postgraduate School, December 1994."December 1994." Dissertation supervisor(s): R.L. Haney. Includes bibliographical references (p. 75-79). Also available online.
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Uriarte, Adolfo. "Sediment dynamics on the inner continental shelf of the Basque country (N. Spain)". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285661.
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Akuetevi, Cataria Quam Cyrille. "Dynamics of turbulent western boundary currents at low latitudes, a numerical study". Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU002/document.
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Les courants turbulents de bord ouest sont l'un des phénomènes les plus dominants des océans, il en existe aux faibles latitudes aussi. Ils sont caractérisés par une dynamique très turbulente avec une forte production d'énergie cinétique, et une forte variabilité interne. Plusieurs régions existent où les courants de bord ouest se rétrofléchissent (décollage de la côte) pour former des structures cohérentes: des anticyclones, des bursts (arrachements) et des dipoles. Circulant le long de la côte, les courants de bord ouest interagissent très fortement avec le bord ouest et la bathymétrie et sont donc un problème de couche limite. Cependant aucune étude du point de vue de la théorie de couche limite n'a été jamais été faite. Cette thèse aborde le problème d'un point de vue de couche limite par l'utilisation d'un modèle idéalisé "shallow water" à très haute résolution (2.5km) afin d'isoler et de comprendre les processus. Les résultats sont ensuite appliqués à des sorties de modèle réaliste Drakkar (~10km) basé sur le code NEMO. Le courant de Somali est ensuite pris pour cette applicationStrong western boundary currents are one of dominant features of the world oceans, also at low latitudes. They exhibit a turbulent dynamics and their region is a source of strong kinetic energy production and internal variability of the worlds oceans. Several places exists where the western boundary currents retrofect (i.e separation from the coast) and generate coherent structures as anticyclonic eddies, bursts and dipoles. The dynamics of turbulent western boundary currents has so far not been extensively studied in the viewpoint of turbulent boundary-layer theory. The approach followed in this thesis is to use a fine resolution (2.5km) reduced-gravity shallow water model to understand the turbulent boundary-layer processes and then apply these findings to the Ocean General Circulation Model NEMO in the Drakkar configuration (~10km). The case of the Somali Currentis considered for this application
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Lingel, Sherrill Lee. "Scaling effects on the mixing processes of lock-exchange gravity currents /". Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/10149.
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Thomas, Ian Martin. "Numerical studies of the effect of shelf-edge topography on the stability of along-slope currents". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246230.
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Fairweather, Luke. "Mechanisms of supra MTD topography generation and the interaction of turbidity currents with such deposits". Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=215569.
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Mass-transport deposits (MTDs) are virtually ubiquitous on the modern seafloor and common in ancient slope successions. Their upper surfaces are often irregular due to surface topography, which may vary significantly in wavelength and geometry. Turbidity currents are highly sensitive to topography, resulting in the modification of their density and velocity profiles during topographic interaction, thus affecting their depositional architecture. It is therefore expected that supra-MTD turbidite systems are also affected so. Previous analysis of the upper surface of MTDs and conformable overlying turbidite systems suggests that the upper surface of MTDs support irregularities that vary in wavelength, from 10 m to greater than 1000 m, by which longer length-scales may compartmentalise turbidite systems. But such studies do not investigate in detail the mechanisms by which topography is generated and the effect of the three-dimensional form of topography on supra-MTD turbidite systems. This study therefore addresses these aspects by the application of spectral analysis methods, synthetic modelling of three-dimensional topography, and architectural and lithofacies relationships of turbidite systems with the upper surface of MTDs, illustrated using an ancient slope succession cropping out at Cerro Bola, Argentina, and a modern deepwater system of the Sabah slope, offshore Brunei. In this thesis, an analytical model is described that characterises the three-dimensional form of the upper surface of MTDs in to two types: isolated topographic highs (termed positive topography) and isolated topographic lows (termed negative topography), which describe topography with a low and high degree of confinement, respectively. The geometry of these 'types' of topography are illustrated to vary significantly depending on the variability in the confinement across the surface in question, the degree of anisotropy and the obliquity of the flow direction to its orientation, which are similarly quantified using the analytical model described. Such topographic variability and anisotropy are demonstrated to relate to horizontal variations in thickness of the underlying MTD, generated by various mechanisms, including: internal structure, basal shear surface topography and post-emplacement creep and compaction. Each mechanism may support a variety of wavelengths that typically vary in length-scale and are generated simultaneously upon syn- and post-MTD emplacement. As a consequence, a turbidity current may interact with multiple length-scales of topography that might be produced contemporaneously with deposition. Topographic interaction may therefore not occur over the same length-scale as topographic ponding and, thus, supra-MTD ponded turbidite systems may have vertical and horizontal facies transitions that occur over similar length and height scales to the underlying topography despite ponding over a longer wavelength. Due to the three-dimensional complexity and variability of MTD topography, facies and architectures of supra-MTD reservoirs cannot be generalised in two-dimensions or extrapolated with ease into the third-dimension from isolated exposures/data.
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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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Connor, Erin Grace. "Blade dynamics and flux measurements for model seagrass blades in waves and currents". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/95573.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 113-117).
Complex interactions between flow conditions, blade posture, and mass transport processes, represent a challenge to fully understanding the influence of hydrodynamic conditions on the flux of nutrients to the blade surface of submerged aquatic vegetation. To isolate the physical mechanisms from biological processes, model seagrass blades constructed from low-density polyethylene (LDPE) film were used as a laboratory proxy. In accordance with previous studies of LDPE, the balance of the drag force due to fluid motion and the restoring force due to blade stiffness determined the blade posture in unidirectional flow and the relative motion in oscillatory flow. The blade rigidity was adjusted by changing either the blade length or the blade thickness. Horizontal force measurements showed that the reconfiguration of blades in flow resulted in a less than quadratic power-law relation between force and velocity. Specifically, F - U³/⁴. Two techniques and two tracer chemicals (dibromochloromethane and 1,2-dichlorobenzene) for estimating uptake by LDPE, as an analogue to nutrient uptake by seagrass, are described and compared. Mass uptake by blades during flux experiments demonstrated mixed control by both the LDPE-side and water-side mass transfer velocities. In experiments using 1,2-dichlorobenzene, measured uptake was fit to a numerical diffusion model to estimate the water-side transfer velocity. The water-side transfer velocity had a non-linear dependence on velocity in that the rate of increase of the mass transfer velocity decreased with greater blade bending in flow.
by Erin Grace Connor.
S.M.
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Meuleners, Michael Joseph. "A numerical study of the mesoscale eddy dynamics of the Leeuwin Current system". University of Western Australia. School of Environmental Systems Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0134.
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[Truncated abstract] The study of eastern ocean boundary currents has been principally restricted to the Pacific and Atlantic ocean regions. The traditional view of the circulation near eastern ocean boundaries is that upwelling-favourable winds force surface waters offshore, leading to upwelling of cold, nutrient-rich subsurface water at the coast, the formation and offshore advection of a coastal front, and the generation of alongshore currents, generally having an equatorward surface flow and a poleward undercurrent. The eastern ocean boundary system of the southern Indian Ocean, off the west coast of Australia, is unique compared with these regions because a warm, poleward surface flow, known as the Leeuwin Current, dominates the dynamics over the continental shelf. Satellite imagery has shown the Leeuwin Current consists of a complex system of meanders, jet-like streams, and eddies, and has a seasonal and interannual variability. The oceanic circulation of the region between Carnarvon (latitude 25°S) and Jurien Bay (latitude 31°S) was examined using observational and remotely sensed data in conjunction with a detailed numerical modelling study. The model was validated using in situ ADCP and CTD data, and the horizontal eddy viscosity parameterization was tested against field observations. ... The resulting offshore meander grew laterally, shallowed, and closed to form an anticlockwise eddy to the original clockwise eddy’s south, forming a characteristic LC eddy pair (dipole). The model demonstrated the LC and Leeuwin Undercurrent (LUC) coupling played an important role in the onset of eddies at both sites. When an energy diagnostic scheme was used, the dominant instability process linked to the anticlockwise eddy’s development at site 1 was a mixed mode barotropic and baroclinic instability. The baroclinic instability’s source was the available potential energy stored within the mean lateral density gradient. The LC’s meandering southerly flow interacting with the LUC’s northerly subsurface flow generated the horizontal shear that sourced the barotropic instability. The dominant instability process at site 2 was baroclinic in origin. Possible links between the eddy field dynamics and the shelfslope region’s alongshore topographic variability were considered. The results of a suite of five model runs, differing only in the specification of bottom topography, were contrasted to investigate the effects. Except for the expected alongshore variability, delay in the onset of instabilities, varying growth rates, and some differences in the dominant wavebands’ mesoscale patterns, the overall impression was the response was similar.
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Coutis, Peter F. School of Mathematics UNSW. "Currents, coasts and cays : a study of tidal upwelling and island wakes". Awarded by:University of New South Wales. School of Mathematics, 2000. http://handle.unsw.edu.au/1959.4/18207.
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In this thesis, the phenomenon of flow-topography interaction is considered in the context of two dynamically distinct case studies. In the first study, tidally-driven upwelling is investigated usingfield data collected in Hydrographers Passage (20????S), a narrow, navigable channel in the dense outer reef matrix of the southern Great Barrier Reef, Australia. In the second study, island wake formations at Cato Island (155????32????E, 23????15????S) in the deep, Western Coral Sea are examined using a combination of field data and numerical experiments. The result of the Hydrographers Passage study are of considerable scientific interest since they apply to numerous smaller non-navigable reef-edge passages dotted throughout the southern Great Barrier Reef. Strong, semi-diurnal flood tides flowing through a gap in a distal patch reef system at the shelf break generate strong upwelling, providing a pulsed, semi-diurnal input of nutrients to the reefs offshore of the passage. If stable in the long term, this mechanism could have profound evolutionary implications for large reefal areas in the southern Great Barrier Reef. In the second study, two sets of field observations at Cato Island coincided with conditions of strong (~0.7m s-1), vertically sheared incident currents and weaker (~0.3m s-1), more variable incident flows. The combination of dynamically distinct flow regimes and a tall, steep-sided island penetrating oligotrophic surface waters provides a unique opportunity to investigate the impact of island wakes on hydrographic structure and biological enhancement. Field data indicate that flow disturbances downstream of Cato Island are likely to generate biological enhancement during conditions of eddy shedding and non-shedding wakes. A primitive equation numerical model configured on the basis of field observations faithfully reproduces the key features of both data sets; mechanisms responsible for producing these key features are proposed. Previous numerical studies of island wakes have concentrated primarily on eddy shedding flows. In this thesis, the sub-critical (non-shedding) flow scenario is also considered. It is demonstrated that particle retention in island wakes has a ????hair trigger???? characteristic controlled by incident flow speed. This observation leads to a new proposal to explain the long-standing recruitment problem of biological oceanography.
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Wei, Taoyuan. "The effects of positive gradient breaks on flow and sediment dynamics in density currents". Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534847.
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Gensheimer, Robert James. "Dynamics of particle clouds in ambient currents with application to open-water sediment disposal". Thesis, Cambridge Massachusetts Institute of Technology, 2010. http://hdl.handle.net/10945/4945.
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CIVINSApproved for public release; distribution is unlimited
Open-water sediment disposal is used in many applications around the world, including land reclamation, dredging, and contaminated sediment isolation. Timely examples include the land reclamation campaign currently underway in Singapore and the Boston Harbor Navigation Improvement Project. Both of these projects required the precise dumping of millions of cubic meters of purchased sediment, in the former example, and dredged material (both clean and contaminated), in the latter example. This shows the significant economic and environmental interests in the accurate placement of sediment, which requires knowledge of how particle clouds behave in ambient currents. Flow visualization experiments were performed in a glass-walled recirculating water channel to model open-water sediment disposal by releasing particles quasi-instantaneously into the channel with ambient currents. For releases at the surface, criteria were developed to characterize ambient currents as weak, transitional, or strong as a function of particle size. In weak ambient currents, particle clouds advected downstream with a velocity equal to the ambient current, but otherwise the behavior and structure was similar to that in quiescent conditions. The parent cloud's entrainment coefficient (alpha) increased with decreasing particle size and elevation above the water surface, between values of 0.10 and 0.72, but for most experiments, the range was less significant (0.11 to 0.24). A substantial portion of the mass initially released, up to 30%, was not incorporated into the parent cloud and formed the trailing stem. This was also heavily dependent on the initial release variables, with the greatest sensitivity on particle size. The loss of sediment during descent, defined as the fraction of mass missing a designated target with a radius equal to the water depth, was quantified and found to increase sharply with current speed.
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Gensheimer, Robert James III. "Dynamics of particle clouds in ambient currents with application to open-water sediment disposal". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/60709.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 255-259).
Open-water sediment disposal is used in many applications around the world, including land reclamation, dredging, and contaminated sediment isolation. Timely examples include the land reclamation campaign currently underway in Singapore and the Boston Harbor Navigation Improvement Project. Both of these projects required the precise dumping of millions of cubic meters of purchased sediment, in the former example, and dredged material (both clean and contaminated), in the latter example. This shows the significant economic and environmental interests in the accurate placement of sediment, which requires knowledge of how particle clouds behave in ambient currents. Flow visualization experiments were performed in a glass-walled recirculating water channel to model open-water sediment disposal by releasing particles quasi-instantaneously into the channel with ambient currents. For releases at the surface, criteria were developed to characterize ambient currents as "weak," "transitional," or "strong" as a function of particle size. In "weak" ambient currents, particle clouds advected downstream with a velocity equal to the ambient current, but otherwise the behavior and structure was similar to that in quiescent conditions. The parent cloud's entrainment coefficient (??) increased with decreasing particle size and elevation above the water surface, between values of 0.10 and 0.72, but for most experiments, the range was less significant (0.11 to 0.24). A substantial portion of the mass initially released, up to 30 %, was not incorporated into the parent cloud and formed the trailing stem. This was also heavily dependent on the initial release variables, with the greatest sensitivity on particle size. The "loss" of sediment during descent, defined as the fraction of mass missing a designated target with a radius equal to the water depth, was quantified and found to increase sharply with current speed. The cloud number (Nc), which relates the particle settling velocity to a characteristic thermal descent velocity, provides a basis for scaling laboratory results to the real world and formulating guidelines to reduce the losses that could result from open-water sediment disposal.
by Robert James Gensheimer, III.
S.M.
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Louw, Gavin Shaun. "Monitoring the dynamics of the Agulhas Current System off Port Edward, Kwazulu-Natal". Thesis, Cape Peninsula University of Technology, 2014. http://hdl.handle.net/20.500.11838/2032.
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Thesis submitted in fulfilment of the requirements for the degree
Master of Technology: Oceanography
in the Faculty of Applied Sciences
at the Cape Peninsula University of TechnologyIn order to validate remote sensing products and to provide data for model assimilation, a real-time monitoring line consisting of three moorings was deployed across the Agulhas Current off Port Edward, South Africa. This deployment formed part of a Technology and Human Resource for Industry Programme (THRIP) funded initiative to develop a real-time mooring system capable of measuring ocean parameters in the Agulhas Current during 2011. The slope and offshore moorings displayed a distinct stratified regime within the Agulhas Current, a northeastward flowing Agulhas Undercurrent and the southwestward flowing Agulhas Current. Three major reversal events, with northeastward currents occurred on 23 July, 02 September and on 11 October 2011. All current reversals caused a decrease in current velocity. The Agulhas Undercurrent was a persistent feature and average velocities between the line of moorings ranged between 13.38 cm/s and 15.52 cm/s. The results obtained from the mooring systems were consistent in terms of velocity, direction and hydrographic properties of the Agulhas Current as described in previous literature. The low directional variability in the surface layers at the offshore mooring and dominant southwestward flow, except during reversal events indicate the strong influence of the Agulhas Current in this region. The inshore mooring showed less occurrences of the Agulhas Undercurrent if northward flow in the bottom layers was to be considered as signs of the Agulhas Undercurrent. General current characteristics as well as the characterisation of the mesoscale features affecting the coast off Port Edward was accomplished through the use of the in situ moorings. All current reversals encountered were associated with the process of vortex shedding from the Natal Bight. These events may be related to the shedding of the Durban Cyclonic Eddy from its origin in the Natal Bight. Data from the offshore mooring suggested that for monitoring Agulhas Current core dynamics, it was ideally placed as highest surface velocities were measured by this mooring system. The slope mooring recorded highest velocities within the Agulhas Undercurrent and was thus ideally placed to measure the Agulhas Undercurrent’s core. Shelf dynamics were under the influence of the Agulhas Current and northerly current reversals and were aptly recorded by the inshore mooring which was placed on the continental shelf, close to the shelf break.
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Musiak, Jeffery Daniel. "Three-dimensional circulation dynamics of along-channel flow in stratified estuaries /". Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/6823.
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Tilston, Michael Christopher. "The Role of Particle Size and Concentration in Defining the Flow Structure of Turbidity Currents and the Morphology of their Deposits: Insights from Computed Tomography". Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/35828.
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Turbidity currents are turbulent particle suspensions that are the primary mechanism for transporting terrestrial sediments to the deep marine, and generate some of the largest depositional features on Earth. However the fluid-particle interactions that sustain these currents are poorly understood, principally due to the technical challenges posed by obtaining accurate velocity and density measurements, which are critical for describing flow behavior and depositional characteristics. Numerous studies have bypassed these issues by using saline density currents, but this negates the ability to link flow processes with depositional features, and it is unclear whether their density structures are representative of particle gravity flows. Consequently, numerous questions remain over the flow conditions that build up a significant part of the deep-marine geologic record.
In this thesis I reports on the flow processes and depositional features of sediment-gravity currents across a broad range of particle sizes and concentrations. The technical challenges of obtaining reliable density data are overcome by running the experimental flows through a medical grade computed tomography (CT) scanner, and pair this data with three-dimensional velocity measurements using an ultrasonic Doppler velocity profiler (UDVP-3D) to get one of the first glimpses of the internal structure of turbidity currents. Unlike previous studies where flow processes are described in terms of the velocity field, this thesis demonstrates that fluid-particle interactions are controlled by momentum characteristics, and that the velocity field is determined largely by the current’s density structure. Moreover, the density structure also exerts a first order control on the morphology of their deposits.
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Hancke, Lisa. "Dynamics of the Tsitsikamma current, with implications for larval transportof chokka squid (Loligo reynaudii) on the eastern Agulhas Bank". Thesis, Cape Peninsula University of Technology, 2010. http://hdl.handle.net/20.500.11838/2035.
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Thesis (MTech (Oceanography))Cape Peninsula University of Technology, 2010The current dynamics along the Tsitsikamma coast is described from a combination of acoustic current measurements. satellite-tracked surface drifters and underwater temperature recordings made between November 2006 and March 2008. The Tsitsikamma coast is largely a Marine Protected Area (MPA) that protects a rich marine biodiversity. The nearshore currents are important in the dispersal of eggs and larvae of many marine species. including the paralarvae of the commercially caught chokka squid. LoNgo reynaudii. Changes in the environment, including the currents. can affect the successful recruitment of chokka squid, and can bring about large annual fluctuations in biomass that creates economic uncertainty in the squid fishery. Results confirm the existence of a predominantly alongshore current off the Tsitsikamma coast. At Middelbank eastward flow was slightly dominant, with a percentage occurrence of 58% vs. 41% westward flow near the surface. The percentage eastward flow decreased with depth, with 41% vs. 58% westward flow near the seabed. At Thyspunt westward and eastward flow occurred at near equal percentages. but westward flow was slightly dominant throughout the water column. The alongshore current was strongest near the surface during eastward flow (maximum = 141 crn.s1: average = 27 crn.s '). while westward surface currents were weaker (maximum velocity = 78 cm.s1: average = 19 crn.s1). Current speed generally decreased with depth and opposing surface and bottom currents, associated with a thermal stratified water column, were occasionally recorded. The nearshore flow regime was characterised by frequent barotropic alongshore reversals that occurred year round. An increase in strong eastward episodes, and opposing surface and bottom currents during spring and summer months have implications for the dispersal of squid paralarvae during the summer and winter spawning seasons. In summer, the combination of strong eastward pulses in the current and upwelling at the capes favoured dispersal onto the midshelf of the Agulhas Bank. In winter, alongshore oscillations without the offshore displacement associated with upwelling. restricted offshore dispersal which caused surface particles to be retained inshore. Drifter trajectories show that both the eastward and westward nearshore current can link the inshore spawning grounds with the nursery grounds, offshore on the central Agulhas Bank; and that passive, neutrally buoyant material in the surface layer can reach the vicinity of the cold ridge in as little as eight days. The wind-driven processes of upwelling and coastal trapped waves (CTWs). and the influence of the greater shelf circulation are discussed as possible driving forces of variability in the currents off the Tsitsikamma coast. The occurrence of coastal trapped waves during thermal stratification appears to drive the jet-like, eastward pulses in the current. and results suggest that the propagation of CTWs may regulate and even enhance upwelling and downwelling along the Tsitsikamma coast.
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Elge, Murat. "Langmuir circulations in a coastal environment during CBLAST". Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Sept%5FElge.pdf.
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Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, Sept. 2004.Thesis advisor(s): Timothy P. Stanton. Includes bibliographical references (p. 95-99). Also available online.
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Денисов, Станіслав Іванович, Станислав Иванович Денисов, Stanislav Ivanovych Denysov, Ганна Валеріївна Бабич, Анна Валерьевна Бабич, Hanna Valeriivna Babych, Людмила Анатоліївна Денисова, Людмила Анатольевна Денисова, Liudmyla Anatoliivna Denysova e Ye A. Peredriy. "Effective Landau-Lifshitz-Gilbert Equation for a Conducting Nanoparticle". Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35362.
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We study the role of conductivity in the magnetization dynamics of single-domain ferromagnetic particles.
Our approach is based on the coupled system of Maxwell’s and Landau-Lifshitz-Gilbert (LLG) equations
that describes both the induced electromagnetic field and the magnetization dynamics. We show that
the effective LLG equation for a conducting particle contains two additional terms compared to the ordinary
LLG equation. One of these terms accounts for the magnetic field of eddy currents induced by an external
magnetic field, and the other is magnetization dependent and is responsible for the conductivity
contribution to the damping parameter. By analytically solving Maxwell’s equations, we determine this
contribution and demonstrate the importance of conduction effects for large nanoparticles.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35362
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Stagraczyński, Stefan Piotr [Verfasser]. "Magnetic dynamics and spin currents in quantum spin systems strongly coupled to environment / Stefan Piotr Stagraczyński". Halle, 2017. http://d-nb.info/114951289X/34.
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Elisabetta, Olivo. "Depositional Processes on the continental slope of Ross Sea (Antarctica) during the Cenozoic in relation with the ice sheet and sub bottom currents dynamics". Doctoral thesis, Università di Siena, 2019. http://hdl.handle.net/11365/1078234.
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The southeastern Ross Sea outer shelf and slope are key areas to study the interactions between oceanic and glacial dynamics on a high latitude continental margin.
I present a multidisciplinary study with the integration of geological, geophysical and oceanographic dataset, derived from the seismic database SDLS (Antarctic Seismic Data Library System), as well as from new acquisitions, in order to reconstruct the slope and rise processes of the Eastern Ross Sea and to propose a depositional model of the margin evolution.
As part of the PNRA (National Antarctic Research Program) - WHISPERS project, during the XII Antarctic expedition of the research vessel OGS Explora (January-March 2017) new data were acquired and subsequently interpreted for this thesis: multibeam bathymetric profiles, single-channel seismic profiles, sub-bottom chirp profiles, XBT (Expandable Bathy-Thermograph) data and ADCP (Acoustic Doppler Current Profiler) data, on the easternmost edge of the Ross Sea (generally covered by sea ice).
During the Cenozoic, the continental slope of the Eastern Ross Sea was affected by several changes, caused by erosion and deposition made by glaciers (ice streams) and bottom currents, in response to sea level and climate changes.
The main facies, discordances and sequences in the entire study area, allow recognizing three important phases of evolution of the continental margin:
• Pre-Miocene - Lower Miocene: the study area is influenced by glaciers and ice streams coming from west-south-west, presumably connected to the EAIS (East Antarctic Ice Sheet) dynamics;
• Middle-Upper Miocene: in the study area there is a transition to a greater contribution of glaciers coming from the south, presumably connected to the WAIS (West Antarctic Ice Sheet) dynamic;
• Lower Pliocene - current time: the sediment deposition by ice streams becomes more confined, the over deepening of the continental shelf and the construction of trough-mouth fans mark a transition to a colder regime.
The most investigated area covers the outer shelf and the upper-medium continental slope, in the southern and eastern part of the Ross Sea. The area is located between the Houtz and the Hayes Bank, at the mouth of the Whales Deep Basin and includes the Ross Sea, Whispers, Explora and Shackleton Canyons.
The oceanographic dataset measured in 2017 suggest that currently, in this area, Antarctic Bottom Water formation occurs because of mixing between the cold and dense Ross Sea Bottom Water and the relatively warm Circumpolar Deep Water (which encroaches the continental shelf).
The analysis of geological and geophysical data allowed to identify and interpret different types of structures, including gullies, canyons, channels, mounds, ridges, slide scars, iceberg scours and mega-scale glacial lineations, useful to reconstruct the presence of preferential route for melt waters flow and possible trajectories used by bottom currents.
The analysis and correlation of the seismic units from the shelf to the slope, completed with the DSDP 271 and IODP U1522 information, suggest that the continental margin underwent at least 4 main episodes of ice shelf advance and retreat, since 2 Ma (possibly starting from 0.65 Ma).
These episodes are highlighted by erosional surfaces, chaotic facies sequences, small-scale incisions and channels, both on the shelf and the slope. Locally, prograding wedges are observed up to the continental shelf edge.
The thickness and the distribution of those units vary, suggesting a relocation through time of the main sediments depocenters presumably indicative of changes in the mechanisms at the origin of sediment supply.
Along the slope, in front of the central part of the Whales Deep Basin, the thickness of the most recent seismic unit is maximum and the current shelf edge presents a convex shape. The slope gradient is 5-10° degrees and the multibeam and the seismic sections highlight the presence of slide scars (on the upper slope) and a lobed-shaped deposit (on the lower slope). This geomorphological arrangement is interpreted as the expression of glacial deposit, resulting from an ice stream activity that occurred in front of the central part of the Whales Deep Basin, and was affected by gravitational instability after its deposition along the slope.
In the slope areas located in front of both lateral extremities of the Whale Deep basin, the thickness of the most recent seismic unit is minimal and the current shelf edge presents a concave shape. In those areas, instead dominated by erosion, the slope gradient is >10° and the multibeam reveals more incised structures on the current seabed, with well-developed gullies at the shelf edge.
This area, mostly dominated by erosion, can be expression of different processes that prevented the accumulation or removed sediments: preferential route for the melt water, discharged into the sea during the ice retreat that flowed along the Whales Deep at the end of the LGM; and/or corridors for the cold and dense waters formed in the Ross Sea discharge.
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Muir, Christine. "The dynamics of intense long-term motivation in language learning : Directed Motivational Currents in theory and practice". Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/33810/.
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Directed Motivational Currents (DMCs) are a novel motivational construct which describe periods of highly motivated behaviour while working towards a well-defined and personally significant end goal (see e.g. Dörnyei, Henry & Muir, 2016). Such periods of motivation are found in diverse contexts and directed towards varied outcomes, yet are uniquely recognisable by the highly positive emotionality exhibited by individuals, who during this time often surpass even their wildest expectations. To date, DMC research has focused on qualitative accounts of the personal experiences of DMCs, and while this has offered a wealth of comprehensive data, key research strands remain unexplored. In response to this, this thesis comprises two complementary studies, each looking at a novel aspect of DMC theory and application. Study 1 takes a quantitative approach to research by addressing questions related to the recognisability of DMCs across continents and contexts, and considers basic questions such as how many people report having experienced periods of DMC-like motivation, what inspired them, and the durations they lasted. It additionally looks at the demographic factors of respondents to understand whether there are links between DMCs and either gender, age or nationality. The study uses a newly developed online questionnaire tool and involves a total of 1563 participants of 71 different nationalities. The results support the notion that DMCs are a well-recognisable and widely experienced motivational phenomenon in society, and indicate no significant links between DMCs and any demographic factors. In terms of language learning, the findings support the assertion that DMCs are found across a wide range of language levels and contexts. Study 2 addresses the practical applicability of DMC theory to language learning and teaching. This classroom intervention study – conducted in collaboration with Jessica Florent and David Leach – aimed to purposefully facilitate a group DMC experience in a class of 16 business English language learners. The basis of this study stems from the observation that within a classroom context, group DMCs can be thought of as intensive group projects. The study was structured around an ‘All Eyes on the Final Product’ project framework (Dörnyei et al., 2016), the end goal being the organisation of a large charity fundraising event. Data was collected throughout the five weeks from personal diary entries and Skype interviews with both students and teachers. Findings suggest the intervention was highly successful in creating a group DMC experience, and significantly, it was also found that students reported notable positive developments throughout the course, both in terms of their language learning and in other key skills. The cumulative conclusions presented in this thesis are therefore highly encouraging, offering strong empirical support to the claim that DMCs are a well-recognised and widely experienced motivational phenomenon which transcends borders and contexts. Results equally suggest that the purposeful facilitation of DMC experiences with varied groups of language learners in diverse contexts – to achieve dual motivational and educational aims – might be a very real possibility. Although positive results are reported, both studies venture into previously unchartered research territory and, in light of this, the conclusions put forward require validation and confirmation through further empirical work. Suggestions for future research are made.
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Palma, Jesse T. "Sigmoid signaling and pattern processing by spiking cortical circuits: after-hyperpolarization currents, acetylcholine, and recurrent competitive dynamics". Thesis, Boston University, 2012. https://hdl.handle.net/2144/31593.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
Recurrent networks in which neurons interact with their neighboring cells are ubiquitous in the brain, where they enable a diverse set of transformations during perception, cognition, emotion, and action. It has been known since the 1970's how the choice of feedback signal functions within rate-based recurrent on-center off-surround networks can control the transformation of input patterns into activity patterns that are stored in short term memory, and eventually learned in long term memory. A sigmoid signal function may, in particular, control a quenching threshold below which inputs are suppressed as noise and above which they may be contrast-enhanced before the pattern is stored. The threshold and slope of the sigmoid signal function determine the degree of noise suppression and contrast enhancement. This dissertation analyses how sigmoid signal functions may be shaped and controlled in biophysically realistic spiking neurons. Combinations of fast, medium, and slow after-hyperpolarization (AHP) currents, and their modulation by acetylcholine (ACh), can control sigmoid signal threshold and slope. Simulations demonstrate how these changes in signaling impact pattern processing by recurrent on-center off-surround circuits. The results include network connectivity that is global, distance-dependent, and interneuron-mediated. With an appropriate degree of recurrent excitation and inhibition, spiking networks maintain a partially contrast-enhanced pattern for 800 milliseconds or longer after stimulus termination, then resolve to no stored pattern, or to winner-take-all stored patterns with one or multiple winners. Strengthening inhibition prolongs a partially contrast-enhanced pattern by slowing the transition, while strengthening excitation causes more winners when the network stabilizes. These dynamics are sensitive to changes in AHP currents due to ACh influx, namely a decrease in the threshold and an increase in the slope of the transfer function. The effect can lengthen the persistence of a partially contrast-enhanced pattern, increase the number of winners, or, if connectivity is distance-dependent, cause cell activities to cluster. These results clarify how cholinergic modulation by basal forebrain circuits may alter the vigilance of category learning circuits, and thus their sensitivity to predictive mismatches, thereby controlling whether learned categories code concrete or abstract information, as predicted by Adaptive Resonance Theory.
2031-01-01
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Cartwright-Taylor, A. L. G. "Deformation-induced electric currents in marble under simulated crustal conditions : non-extensivity, superstatistical dynamics and implications for earthquake hazard". Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1471386/.
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This thesis investigates electric current signals generated spontaneously in specimens of Carrara marble during deformation under crustal conditions. It extends previous work where similar currents were observed during uniaxial deformation of marble. Since marble is a non-piezoelectric material, one of the main questions is how these currents are related to the mechanical processes of deformation. Another question is whether it is possible to extract from these electric currents information about the deformation dynamics. This is particularly important in light of recent claims that geoelectric anomalies observed in the field are related to crustal deformation and can inform us about changes in the organisation of the fault network in a focal region prior to an earthquake. Using an approach that combines rock deformation experiments and statistical modelling, I examine how these electric currents evolve with deformation at the laboratory scale and make several original discoveries regarding their behaviour. To establish how the current signals varied with experimental condition and deformation mechanism across the brittle-ductile transition, I conducted constant strain rate triaxial compression experiments recording differential electric current flow through the rock samples at various confining pressures, strain rates and pore fluid conditions. I acquired mechanical data, ultrasonic velocities and acoustic emissions simultaneously, along with electric current, to constrain the relationship between electric current and deformation. For the statistical modelling, I used a novel entropy-based model, derived from non-extensive statistical mechanics (Tsallis, 1988), which has the advantage of including a term to account for interactions in the system. Interactions are effectively modelled by the non-extensive q-parameter. Small (nanoAmpere) electric currents are generated and sustained during deformation under all the conditions tested. Spontaneous electric current flow in the dry samples is seen only in the region of permanent deformation and is due to the presence of localised electric dipoles. This current flow is correlated to the damage induced by microcracking, with a contribution from other intermittent ductile mechanisms. Current and charge densities are consistent with proposed models of crack separation charging and migrating charged edge dislocations. The onset of current flow occurs only after a 10% reduction in P-wave velocity, implying that some degree of crack damage and/or crack connectivity is required before current will flow through the samples. Electric current evolution exhibits three separate time-scales of behaviour, the absolute and fluctuating components of which can be related to the evolution of stress, deformation mechanism, damage and localisation of deformation leading up to sample failure. In the brittle regime, electric current exhibits a precursory change as the stress drop accelerates towards failure, which is particularly distinct at dynamic strain rates. Current and charge production depend strongly on the experimental conditions. Power-law relationships are seen with confining pressure and strain rate, with the first corresponding to increased microcrack suppression and the second to time-dependent differences in deformation mechanism across the brittle-ductile transition. In the presence of an ionic pore fluid, electrokinetic effects dominate over solid-state mechanisms but development of the crack network and charge contribution from solid-state deformation processes drive the variation in electrokinetic parameters. Current flow in the dry samples is approximately proportional to stress within 90% of peak stress. In the fluid-saturated samples, proportionality holds from 40% peak stress, with a significant increase in the rate of current production from 90% peak stress, and is associated with fluid flow during dilatancy. This proportionality, together with the power-law relationship between current and strain rate is reminiscent of power-law creep, where deformation rate varies as a power-law function of stress, and suggests that the electric signals could be used as a proxy for stress. High frequency fluctuations in the electric current signal can be described by `fat-tailed' q-Gaussian statistics, consistent with an origin in non-extensive statistical mechanics. These distributions can be explained as arising from superstatistical dynamics (Beck, 2001; Beck and Cohen, 2003), i.e., the superposition of local mechanical relaxations in the presence of a slowly varying driving force. The macroscopic distribution parameters provide an excellent prediction of the experimentally observed mean energy dissipation rate of the system (as modelled by the superstatistical β-parameter), particularly at slow strain rates. Furthermore, characteristic q-values are obtained for different deformation regimes across the brittle-ductile transition, and the evolution of q during deformation reveals a two-stage precursory anomaly prior to sample failure, consistent with the stress intensity evolution as modelled from fracture mechanics. These findings indicate that the dynamics of rock deformation are reflected in the statistical properties of the recorded electric current. My findings support the notion that electric currents in the crust can be generated purely from deformation processes themselves. Scaling up the laboratory results to large stressed rock volumes at shallow crustal pressures and constant crustal strain rates, deformation induced transient telluric current systems may be as large as 1 MA, even accounting for >99% dissipation, which corresponds to a huge accumulated net charge of 10 ZC. This implies that a significant amount of charge from deforming tectonic regions contributes to the Earth's telluric currents and electric field, although due to conduction away from the stressed rock volume, it is unlikely that accumulated charge of this quantity would ever be measured in the field. Electric current evolution and its precursory characteristics can be related to models for electric earthquake precursors and fault-zone damage organisation, developed from field observations, providing experimental support for them. However, given the oscillatory nature of the current evolution observed during cataclastic flow processes in the laboratory, there is a high probability of false alarms. Furthermore, the potential for electric anomalies to be useful as earthquake precursors remains contentious due to the difficulties of separating deformation-induced signals from other telluric noise and the wider issue of establishing a statistically significant link with earthquakes.
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Wobus, Fred. "The dynamics of dense water cascades : from laboratory scales to the Arctic Ocean". Thesis, University of Plymouth, 2013. http://hdl.handle.net/10026.1/1610.
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The sinking of dense shelf waters down the continental slope (or “cascading”) contributes to oceanic water mass formation and carbon cycling. Cascading is therefore of significant importance for the global overturning circulation and thus climate. The occurrence of cascades is highly intermittent in space and time and observations of the process itself (rather than its outcomes) are scarce. Global climate models do not typically resolve cascading owing to numerical challenges concerning turbulence, mixing and faithful representation of bottom boundary layer dynamics. This work was motivated by the need to improve the representation of cascading in numerical ocean circulation models. Typical 3-D hydrostatic ocean circulation models are employed in a series of numerical experiments to investigate the process of dense water cascading in both idealised and realistic model setups. Cascading on steep bottom topography is modelled using POLCOMS, a 3-D ocean circulation model using a terrain-following s-coordinate system. The model setup is based on a laboratory experiment of a continuous dense water flow from a central source on a conical slope in a rotating tank. The descent of the dense flow as characterised by the length of the plume as a function of time is studied for a range of parameters, such as density difference, speed of rotation, flow rate and (in the model) diffusivity and viscosity. Very good agreement between the model and the laboratory results is shown in dimensional and non-dimensional variables. It is confirmed that a hydrostatic model is capable of reproducing the essential physics of cascading on a very steep slope if the model correctly resolves velocity veering in the bottom boundary layer. Experiments changing the height of the bottom Ekman layer (by changing viscosity) and modifying the plume from a 2-layer system to a stratified regime (by enhancing diapycnal diffusion) confirm previous theories, demonstrate their limitations and offer new insights into the dynamics of cascading outside of the controlled laboratory conditions. In further numerical experiments, the idealised geometry of the conical slope is retained but up-scaled to oceanic dimensions. The NEMO-SHELF model is used to study the fate of a dense water plume of similar properties to the overflow of brine-enriched shelf waters from the Storfjorden in Svalbard. The overflow plume, resulting from sea ice formation in the Storfjorden polynya, cascades into the ambient stratification resembling the predominant water masses of Fram Strait. At intermediate depths between 200-500m the plume encounters a layer of warm, saline AtlanticWater. In some years the plume ‘pierces’ the Atlantic Layer and sinks into the deep Fram Strait while in other years it remains ‘arrested’ at Atlantic Layer depths. It has been unclear what parameters control whether the plume pierces the Atlantic Layer or not. In a series of experiments we vary the salinity ‘S’ and the flow rate ‘Q’ of the simulated Storfjorden overflow to investigate both strong and weak cascading conditions. Results show that the cascading regime (piercing, arrested or ‘shaving’ - an intermediate case) can be predicted from the initial values of S and Q. In those model experiments where the initial density of the overflow water is considerably greater than of the deepest ambient water mass we find that a cascade with high initial S does not necessarily reach the bottom if Q is low. Conversely, cascades with an initial density just slightly higher than the deepest ambient layer may flow to the bottom if the flow rate Q is high. A functional relationship between S/Q and the final depth level of plume waters is explained by the flux of potential energy (arising from the introduction of dense water at shallow depth) which, in our idealised setting, represents the only energy source for downslope descent and mixing. Lastly, the influence of tides on the propagation of a dense water plume is investigated using a regional NEMO-SHELF model with realistic bathymetry, atmospheric forcing, open boundary conditions and tides. The model has 3 km horizontal resolution and 50 vertical levels in the sh-coordinate system which is specially designed to resolve bottom boundary layer processes. Tidal effects are isolated by comparing results from model runs with and without tides. A hotspot of tidally-induced horizontal diffusion leading to the lateral dispersion of the plume is identified at the southernmost headland of Spitsbergen which is in close proximity to the plume path. As a result the lighter fractions in the diluted upper layer of the plume are drawn into the shallow coastal current that carries Storfjorden water onto the Western Svalbard Shelf, while the dense bottom layer continues to sink down the slope. This bifurcation of the plume into a diluted shelf branch and a dense downslope branch is enhanced by tidally-induced shear dispersion at the headland. Tidal effects at the headland are shown to cause a net reduction in the downslope flux of Storfjorden water into deep Fram Strait. This finding contrasts previous results from observations of a dense plume on a different shelf without abrupt topography. The dispersive mechanism which is induced by the tides is identified as a mechanism by which tides may cause a relative reduction in downslope transport, thus adding to existing understanding of tidal effects on dense water overflows.
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Bunescu, Costel [Verfasser], Joachim [Akademischer Betreuer] Vogt, Joachim [Gutachter] Vogt, Octav [Gutachter] Marghitu, Gerhard [Gutachter] Haerendel e Rossi Angelo [Gutachter] Pio. "Auroral Field-Aligned Currents: Analysis, Structure, and Dynamics / Costel Bunescu ; Gutachter: Joachim Vogt, Octav Marghitu, Gerhard Haerendel, Angelo Pio Rossi ; Betreuer: Joachim Vogt". Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2017. http://d-nb.info/1148104038/34.
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Stewart, Andrew L. "The role of the complete Coriolis force in cross-equatorial transport of abyssal ocean currents". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:6bf3faff-ec7e-4d11-bdfe-c54ae9d03895.
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In studies of the ocean it has become conventional to retain only the component of the Coriolis force associated with the radial component of the Earth’s rotation vector, the so-called “traditional approximation”. We investigate the role of the “non-traditional” component of the Coriolis force, corresponding to the non-radial component of the rotation vector, in transporting abyssal waters across the equator. We first derive a non-traditional generalisation of the multi-layer shallow water equations, which describe the flow of multiple superposed layers of inviscid, incompressible fluid with constant densities over prescribed topography in a rotating frame. We derive these equations both by averaging the three-dimensional governing equations over each layer, and via Hamilton’s principle. The latter derivation guarantees that conservation laws for mass, momentum, energy and potential vorticity are preserved. Within geophysically realistic parameters, including the complete Coriolis force modifies the domain of hyperbolicity of the multi-layer equations by no more than 5%. By contrast, long linear plane waves exhibit dramatic structural changes due to reconnection of the surface and internal wave modes in the long-wave limit. We use our non-traditional shallow water equations as an idealised model of an abyssal current flowing beneath a less dense upper ocean. We focus on the Antarctic Bottom Water, which crosses the equator in the western Atlantic ocean, where the bathymetry forms an almost-westward channel. Cross-equatorial flow is strongly constrained by potential vorticity conservation, which requires fluid to acquire a large relative vorticity in order to move between hemispheres. Including the complete Coriolis force accounts for the fact that fluid crossing the equator in an eastward/westward channel experiences a smaller change in angular momentum, and therefore acquires less relative vorticity. Our analytical and numerical solutions for shallow water flow over idealised channel topography show that the non-traditional component of the Coriolis force facilitates cross-equatorial flow through an almost-westward channel.
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Pattrick, Paula. "Larval fish dynamics in the shallow nearshore of Eastern Algoa Bay with particular emphasis on the effects of currents and swimming abilities on dispersal". Thesis, Rhodes University, 2008. http://hdl.handle.net/10962/d1005139.
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The larval fish assemblage in the shallow, nearshore region of a proposed marine protected area (MPA) in eastern Algoa Bay, temperate South Africa was investigated. Current velocities and direction and the swimming abilities of late-stage larvae were further assessed to determine potential larval movement to and from the MPA. In total, 6045 larval fishes were collected along two depth contours (~5m and ~15m) in the shallow nearshore of eastern Algoa Bay using stepped-oblique bongo net tows, twice per season for two years (March 2005 – January 2007). These larvae represented 32 families and 78 species. The Gobiidae, Cynoglossidae, Clupeidae, Engraulidae and Sparidae were the dominant fish families. Catches varied significantly between seasons peaking in spring with a mean of 64 larvae/100m3. Preflexion stage larvae dominated catches (75%). All developmental stages of Diplodus capensis, Engraulis capensis, Heteromycteris capensis, Sardinops sagax and Pomadasys species were found in the study area. It appears that these species use the shallow nearshore as a nursery area. Analysis of 12 months (May 2006 – May 2007) data from a bottom-moored Acoustic Doppler Current Profiler within the study area showed that offshore south eastward (39%) and onshore north westward currents (33%) dominated. The south westward current (15%) and north eastward current (12%) occurred less frequently. Current velocity decreased with depth in the nearshore, with a mean velocity of ~29 cms⁻¹ recorded at a depth of 4 m and a mean velocity of ~11 cms⁻¹ recorded at a depth of 14 m. Understanding the dispersal and movement of marine fish larvae in coastal habitats requires knowledge of active swimming abilities. The critical speed and endurance swimming of late stage larvae of two common inshore species occurring in the study area, Diplodus capensis and Sarpa salpa (Family Sparidae), were measured in a laboratory swimming chamber. The mean U-crit value for D. capensis (18.6 cms⁻¹) was similar to that of S. salpa (18.0 cms⁻¹), whereas mean endurance (km swum) was greater in S. salpa (8.4 km) than D. capensis (5.9 km). These swimming abilities exceed the average current velocities observed in the shallow nearshore providing larvae with the ability to greatly alter their passive dispersal trajectories and ultimately influence their distribution in the nearshore.