Dissertations / Theses on the topic 'Current variability'
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1
Tisch, Timothy Daniel. "Seasonal variability of the geostrophic velocity and water mass structure off Point Sur, California." Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241374.
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Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, September 1990.Thesis Advisor(s): Ramp, Steven R. ; Collins, Curtis A. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): California Current. Author(s) subject terms: California Current, California Undercurrent, Spiciness Anomaly, Geostrophic Velocity, Water Mass Characteristics. Includes bibliographical references (p. 142-146). Also available in print.
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Vecchi, Gabriel Andrés. "Sub-seasonal wind variability and El Niño /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/11046.
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Yttervik, Rune. "Ocean current Variability in Relation to Offshore Engineering." Doctoral thesis, Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, 2005. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-499.
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This work adresses ocean current variability in relation to offshore engineering.
The offshore oil and gas activity has up until recently taken place mainly on the continental shelves around the world. During the last few years, however, the industry has moved past the continental shelf edge and down the continental slope towards increasingly deeper waters. In deep water locations, marine structures may span large spaces, marine operations may become more complicated and require longer time for completion and the effect of the surface waves is diminished. Therefore, the spatial and temporal variability of the current is expected to become more important in design and planning than before.
The flow of water in the oceans of the world takes place on a wide variety of spatial scales, from the main forms of the global ocean circulation (~km), to the microstructure (~mm) of boundary layer turbulence. Similarly, the temporal variability is also large. In one end of the scale we find variations that take place over several decades, and in the other end we find small-scale turbulence (~seconds). Different features of the flow are driven by different mechanisms. Several processes and properties (stratification1, sloping boundary, Coriolis effect, friction, internal waves, etc.) interact on the continental slope to create a highly variable flow environment. Analysis of a set of observed data that were recorded close to the seabed on the continental slope west of Norway are presented. The data suggest that some strong and abrupt current events (changes in flow speed of ~0.4 m/s in just a couple of hours) were caused by motions of the deep pycnocline2, driven by variations in the surface wind field. This conjecture is partly supported by numerical simulations of an idealised continental slope and a two-layer ocean. The data also contains an event during which the flow direction at the sea bed changed very rapidly (within a few minutes) from down-slope to up-slope flow. The change in speed during this event was as high as 0.5 m/s.
Another data set has been analyzed in order to illustrate the spatial variation in the current that can sometimes be found. It is shown that the flow in the upper layer is virtually decoupled from the flow in the lower layer at a location west of Norway. This is either caused by bottom topography, stratification or both.
High variability of the current presents new requirements to the way that the current should be modelled by the offshore engineer. For instance, it is necessary to consider which type of operation/structure that is to be carried out or installed before selecting design current conditions. Reliable methods for obtaining design current conditions for a given deep water location have yet to be developed, only a brief discussion of this topic is given herein.
It is shown, through calculations of VIV-response and simulations of typical marine operations, that the variability of the current will sometimes have a significant effect on the response/operation.
1Vertical distribution of density. In a stratified ocean or flow, the density of the water varies in the vertical direction.
2pycnocline=density surface between water masses. The pycnocline between two water masses of different density is defined by the maximum of the density gradient.
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Hill, A. E. "The dynamics and variability of the Scottish coastal current." Thesis, Bangor University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380246.
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Donato, Joseph R. "Seasonal variability in the California Current, a DIECAST model study." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1998. http://handle.dtic.mil/100.2/ADA359109.
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Thesis (M.S. in Meteorology and Physical Oceanography) Naval Postgraduate School, December 1998."December 1998." Thesis advisor(s): Robert L. Haney. Includes bibliographical references (p. 65-67). Also available online.
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Davis, Andrew Murphy. "The spatial structure and interannual variability of California current system." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52236.
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The California Current is the Eastern Boundary Current associated with the North Pacific Subtropical Gyre, transporting cold, nutrient-rich water equatorward. It is also an area of strong mesoscale eddy variance, as well as subsurface zonal currents known as striations. This work examines the causes and variability of these transports using a set of eddy-resolving ocean model simulations.
Large-scale meridional transports are found to be driven interannually by the dominant local pattern of wind stress curl variability. This contrasts with earlier work that suggested that these transports were forced principally by tropically-originating coastal- trapped waves.
While mesoscale eddies possess a large fraction of intrinsic variance, there is a deterministic component as well. North of the Southern California Bight this component is driven by the same pattern of wind forcing. To the south, eddies respond nonlinearly to both atmospheric and oceanic forcing.
Striations are found to develop in response to irregularities in the California coastline. They spin up along with the large-scale circulation, and their magnitude is constrained by the shelf.
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Hicks, Michael R. "Alongshore sub-thermocline variability in the central California current system." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23816.
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Rosenfeld, Leslie Karen. "Tidal band current variability over the Northern California continental shelf." Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/44592.
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Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN.
Vita.
Includes bibliographies.
by Leslie Karen Rosenfeld.
Ph.D.
9
Rouault, Marjolaine. "Agulhas current variability determined from space : a multi-sensor approach." Doctoral thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/8500.
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Includes bibliographical references (p. 119-132).Satellite remote sensing datasets including more than 6 years of high frequency Sea Surface Temperature (SST) imagery as well as surface current observations derived from 18 years of merged-altimetry and over 2 years of Advanced Synthetic Aperture Radar (ASAR) observations are combined to study the variability of the Agulhas Current. The newly available rangedirected surface currents velocities from ASAR, which rely on the careful analysis of the measured Doppler shift, show strong promise for monitoring the meso to sub-mesoscale features of the surface circulation. While the accuracy of ASAR surface current velocities suffers from occasional bias due to our current inability to systematically account for the wind-induced contribution to the Doppler shift signal, the ASAR surface current velocities are able to consistently highlight regions of strong current and shear. The synaptic nature and relatively high resolution of ASAR acquisitions make the ASAR derived current velocities a good complement to altimetry for the study of sub-mesoscale processes and western boundary current dynamics. Time-averaged range-directed surface currents derived from ASAR provide an improved map of the mean Agulhas Current flow, clearly showing the location of the Agulhas Current core over the 1000 m isobath and identifying the region at the shelf edge of the north-eastern Agulhas Bank as one of the most variable within the Agulhas Current. To determine the variability of the Agulhas Current, an algorithm to track the position of the current is developed and applied to the longer merged-altimetry and SST records. Limitations associated with altimetry near the coast favour the use of the SST dataset to track the position of the Agulhas Current in its northern region. In the southern Agulhas, where the current lies further from the coast, altimetry is suited to monitoring the position of the Agulhas Current. The front detection analysis conducted on the SST dataset in the northern Agulhas reveals the complex nature of Natal Pulses. The downstream passage of the Natal Pulses is associated with the generation of secondary offshore meanders at the inshore edge of the current. Perturbations formed during the passage of Natal Pulses evolve rapidly to either dissipate, re-merge with the initial Natal Pulse or in some rare occasion, detach from the Agulhas Current.
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Shinker, Jacqueline J. "Mechanistic controls of North American climate variability /." view abstract or download file of text, 2003. http://wwwlib.umi.com/cr/uoregon/fullcit?p3102189.
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Thesis (Ph. D.)--University of Oregon, 2003.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 145-152). Also available for download via the World Wide Web; free to University of Oregon users.
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Parks, Andrew Brad. "Observing Eddy Variability Using HF Radar in the Straits of Florida." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_theses/174.
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A dual-station high frequency Wellen Radar (WERA), transmitting at 16.045 MHz, has been deployed along the Eastern Florida Shelf (EFS). From September 2004 to June 2005, a moored acoustic Doppler current profiler (ADCP) acquired subsurface current measurements within the radar footprint along the shelf break at 86-m depth. The shallowest ADCP bin located at 14-m depth is used as a comparison for the WERA surface measurements. The RMS differences range from 0.1 to 0.3 m s super -1 between the surface and 14-m depth, with good agreement over most of the period. Regression analyses indicate slopes near unity in the north-south (v-) component and approximately 0.5 for the east-west (u-) component velocities. Following validation of the HF radar surface current measurements, an assessment of the variability and character of eddies in the region is conducted for 2006. Optimal interpolation is utilized to create a uniform 45 km by 45 km grid of surface current data consisting of 1980 points in the inshore portion of the WERA domain. The Okubo-Weiss parameter is used to identify eddies as closed regions with values greater than a threshold of 2*10 super -8 s super -1. This method reveals a total of twenty-two eddy-like features over the year 2006. Given the asymmetric shape of the eddy regions, equivalent radii are computed as an estimate of eddy size with an annual average of 2.6 km. Eddy intensity is measured by maximum relative vorticity in the eddy region with an annual average of approximately 5f, where f is the local Coriolis parameter. Translational velocities are computed from the displacement of peak Okubo-Weiss parameter. This method tends to overestimate eddy speed given the shape-changing nature of the eddy regions. Nonetheless, the average translational velocity is 0.9 m s super -1 with a standard deviation of 0.4 m s super -1. Eddy tracks indicate a unique pattern in which eddies propagate inshore during the period of July to September and offshore during October to December related to position of the FC axis. The periodicity and spatial distribution of eddy events suggest that submesoscale eddy features are "wave-like" and centered along the strong topographical gradients between 200 to 600 m. By applying this methodology to other years of HF radar data, this statement can be tested with statistical confidence. In general, this study has shown the effectiveness of the Okubo-Weiss parameter in identifying eddy regions from a background field with large, ambient vorticity.
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Riddet, Craig. "Monte Carlo study of current variability in UTB SOI DG MOSFETs." Thesis, University of Glasgow, 2008. http://theses.gla.ac.uk/88/.
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The scaling of conventional silicon based MOSFETs is increasingly difficult into the nanometer regime due to short channel effects, tunneling and subthreshold leakage current. Ultra-thin body silicon-on-insulator based architectures offer a promising alternative, alleviating these problems through their geometry. However, the transport behaviour in these devices is more complex, especially for silicon thicknesses below 10 nm, with enhancement from band splitting and volume inversion competing with scattering from phonons, Coulomb interactions, interface roughness and body thickness fluctuation. Here, the effect of the last scattering mechanism on the drive current is examined as it is considered a significant limitation to device performance for body thicknesses below 5 nm. A simulation technique that properly captures non-equilibrium transport, includes quantum effects and maintains computational efficiency is essential for the study of this scattering mechanism. Therefore, a 3D Monte Carlo simulator has been developed which includes this scattering effect in an ab initio fashion, and quantum corrections using the Density Gradient formalism. Monte Carlo simulations using `frozen field' approximation have been carried out to examine the dependence of mobility on silicon thickness in large, self averaging devices. This approximation is then used to carry out statistical studies of uniquely different devices to examine the variability of on-current. Finally, Monte Carlo simulations self consistent with Poisson's equation have been carried out to further investigate this mechanism.
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Mitchell, Douglas A. "Upper current structure and variability in the southwestern Japan/East Sea /." View online ; access limited to URI, 2003. http://0-wwwlib.umi.com.helin.uri.edu/dissertations/dlnow/3112121.
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McLaughlin, Pegeen Amy. "Exploring current approaches to status variability in the seventeenth century Chesapeake." W&M ScholarWorks, 1996. https://scholarworks.wm.edu/etd/1539626034.
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Navarro-Perez, Eleuteria. "Physical oceanography of the Canary current : short term, seasonal and interannual variability." Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318561.
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Makowski, Jessica. "Understanding Transport Variability of the Antarctic Circumpolar Current Using Ocean Bottom Pressure." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4915.
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Previous studies have suggested that ocean bottom pressure (OBP) can be used to measure the transport variability of the Antarctic Circumpolar Current (ACC). The OBP observations from the Gravity Recovery and Climate Experiment (GRACE) are used to calculate transport along the choke point between Antarctica and Australia. Statistical analysis will be conducted to determine the uncertainty of the GRACE observations using a simulated data set.
There has been some evidence to suggest that Southern Hemisphere winds and the Southern Annular Mode (SAM) or the Antarctic Oscillation (AAO) play a significant role in accelerating/decelerating ACC transport, along with some contribution from buoyancy forcing. We will examine whether average zonal wind stress, wind stress curl, local zonal winds, or the SAM are representative of the low frequency zonal mass transport variability.
Preliminary studies suggest that seasonal variation in transport across the Australia-Antarctica choke point is driven by winds along and north of the northern front of the ACC, the Sub Tropical front (STF). It also appears that interannual variations in transport are related to wind variations centered south of the Sub Antarctic Front (SAF). We have observed a strong negative correlation/positive correlation across the STF of the ACC in the Indian Ocean, which suggests wind stress curl may also be responsible for transport variations.
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Brugler, Eric T. "Interannual variability of the Pacific water boundary current in the Beaufort Sea." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/85389.
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Thesis: S.M., Joint Program in Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2013.Includes bibliographical references (pages 133-141).
Between 2002 and 2011 a single mooring was maintained in the core of the Pacific Water boundary current in the Alaskan Beaufort Sea near 152° W. Using velocity and hydrographic data from six year-long deployments during this time period, we examine the interannual variability of the current. It is found that the volume, heat, and freshwater transport have all decreased drastically over the decade, by more than 80%. The most striking changes have occurred during the summer months. Using a combination of weather station data, atmospheric reanalysis fields, and concurrent shipboard and mooring data from the Chukchi Sea, we investigate the physical drivers responsible for these changes. It is demonstrated that an increase in summertime easterly winds along the Beaufort slope is the primary reason for the drop in transport. The intensification of the local winds has in turn been driven by a strengthening of the summer Beaufort High in conjunction with a deepening of the summer Aleutian Low. Since the fluxes of mass, heat, and freshwater through Bering Strait have increased over the same time period, this raises the question as to the fate of the Pacific water during recent years and its impacts. We present evidence that more heat has been fluxed directly into the interior basin from Barrow Canyon rather than entering the Beaufort shelfbreak jet, and this is responsible for a significant portion of the increased ice melt in the Pacific sector of the Arctic Ocean.
by Eric T. Brugler.
S.M.
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Sutherland, David A. (David Alan). "The East Greenland Coastal Current : its structure, variability, and large-scale impact." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43156.
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Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2008.Includes bibliographical references (p. 155-161).
The subtidal circulation of the southeast Greenland shelf is described using a set of high resolution hydrographic and velocity transects occupied in summer 2004. The main feature present is the East Greenland Coastal Current (EGCC), a low-salinity, high velocity jet with a wedge-shaped hydrographic structure characteristic of other surface buoyancy-driven currents. The EGCC was observed along the entire Greenland shelf south of Denmark Strait, while the transect north of the strait showed only a weak shelf flow. This observation, combined with evidence from chemical tracer measurements that imply the EGCC contains a significant Pacific Water signal, suggests that the EGCC is an inner branch of the polar-origin East Greenland Current (EGC). A set of idealized laboratory experiments on the interaction of a buoyant current with a submarine canyon also supported this hypothesis, showing that for the observed range of oceanic parameters, a buoyant current such as the EGC could exhibit both flow across the canyon mouth or into the canyon itself, setting the stage for EGCC formation. Repeat sections occupied at Cape Farewell between 1997 and 2004 show that the along shelf wind stress can also have a strong influence on the structure and strength of the EGCC and EGC on timescales of 2-3 days. Accounting for the wind-induced effects, the volume transport of the combined EGC/EGCC system is found to be roughly constant (-2 Sv) over the study domain, from 68*N to Cape Farewell near 60°N. The corresponding freshwater transport increases by roughly 60% over this distance (59 to 96 mSv, referenced to a salinity of 34.8). This trend is explained by constructing a simple freshwater budget of the EGCC/EGC system that accounts for melt water runoff, melting sea-ice and icebergs, and net precipitation minus evaporation.
(cont.) Variability on inter annual timescales is examined by calculating the Pacific Water content in the EGC/EGCC from 1984-2004 in the vicinity of Denmark Strait. The PW content is found to correlate significantly with the Arctic Oscillation index, lagged by 9 years, suggesting that the Arctic Ocean circulation patterns bring varying amounts of Pacific Water to the North Atlantic via the EGC/EGCC.
by David A. Sutherland.
Ph.D.
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Ragoasha, Moagabo Natalie. "The variability of Lagrangian transport in the southern Benguela Current upwelling system." Doctoral thesis, Faculty of Science, 2020. http://hdl.handle.net/11427/32411.
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This study analyses the physical mechanisms that impact Lagrangian pathways and transport in the southern Benguela upwelling system (SBUS),an environment in which currents are key components of many important ecological processes, including the dispersal of marine larvae. Physical advection by currents is an important mechanism for egg and larvae transport success in the SBUS since the spawning areas and recruitment areas are separated by a long distance. High-resolution numerical model simulations of the SBUS coupled with particle tracking experiments are used to investigate Lagrangian pathways between the Cape Peninsula (34◦S) and St Helena Bay(32◦S) and how they are linked to the oceanic circulation. Transport success, given by the ratio of the number of particles that reach St Helena Bay over the total number of particles released, is used quantify the alongshore connectivity between the two regions. We have identified and quantified the following physical drivers: (i) Benguela Jet, (ii) offshore Ekman transport,(iii) inner shelf poleward current, (iv) mesoscale eddies to be responsible for the spatial and temporal variability of the alongshore connectivity. The Benguela Jet was found to be the dominant driver of the connectivity at both seasonal and interannual timescales. Moreover, the presence of anti-cyclonic eddies near the shelf-edge negatively impact transport success by advecting particles into the open ocean. The opposite occurs with shelf-edge eddies as they transport particles onshore onto the shelf and the Benguela Jet contributing to positive transport success anomalies. These findings will provide a valuable information for the future studies on the role of the physical drivers that impact transport of larvae and eggs.
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Alegre, Norza Sior Ana Renza Paola. "Trophic ecology of jumbo squid and predatory fishes in the Northern Humboldt Current System." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS223/document.
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Ce travail est une contribution à l'étude de l'écologie trophique d'importants prédateurs de la partie Nord du système du Courant de Humboldt (NSCH), le chinchard (Trachurus murphyi), le maquereau (Scomber japonicus) et le calmar géant (Dosidicus gigas). Nous avons caractérisé la variabilité des modes d'alimentation de ces espèces à différentes échelles spatiotemporelles et fourni de nouvelles connaissances sur le comportement alimentaire de ces espèces, définies comme opportunistes par des travaux antérieurs. Pour ce faire, nous avons appliqué une variété de méthodes statistiques à un vaste jeu de données comprenant 27188 estomacs non vides. Sur cette base nous avons décrit l'organisation spatiale de la faune fourrage de ces prédateurs et documenté les changements dans la composition des proies en fonction de la taille de prédateurs et des conditions environnementales. Nos résultats indiquent que l'oxygène dissous jour un rôle clef dans ces processus. Nous avons également résolu un paradoxe sur l'alimentation du calmar géant: pourquoi ils ne se nourrissent guère sur l'immense biomasse d'anchois (Engraulis ringens) présente le long de la côte du Pérou? Nous avons montré que la présence d'une zone de minimum d'oxygène (ZMO) superficielle devant le Pérou pourrait limiter la cooccurrence entre calmars géant et anchois. Pour synthétiser ces résultats, nous avons proposé un modèle conceptuel de l'écologie trophique du calmar géant tenant compte du cycle ontogénétique, de l'oxygène et de la disponibilité des proies. Par ailleurs, nous avons montré que le chinchard et le maquereau se nourrissent des espèces les plus accessibles comme par exemple la galathée Pleurocondes monodon ou les larves zoea. Ces deux prédateurs présentent un chevauchement trophique mais, contrairement à ce qui avait été décrit dans d'autres études, le chinchard n'est pas aussi vorace que le maquereau. Le régime alimentaire de ces poissons est caractérisé par une forte variabilité spatio-temporelle et le talus continental s'avère être une importante frontière biogéographique. La composition du régime alimentaire des poissons prédateurs étudiés n'est pas nécessairement un indicateur cohérent de l'évolution de la biomasse des proies. Les événements El Niño ont eu un faible effet sur le taux de remplissage des estomacs et sur le régime alimentaire du chinchard et du maquereau. Par ailleurs les changements en diversité des proies à échelle décennale contredisent le classique paradigme de corrélation positive entre diversité et température. Finalement, les patrons globaux décrits dans ce travail, illustrent le comportement alimentaire opportuniste, les stratégies de vie et le haut degré de plasticité de ces espèces. Un tel comportement permet de s'adapter aux changements de l'environnementThis work provides a contribution to a better understanding of the trophic ecology of important predators in the Northern Humboldt Current System, the jack mackerel (Trachurus murphyi), the chub mackerel (Scomber japonicus) and the jumbo squid (Dosidicus gigas) by the characterization of the highly variable feeding patterns of these species at different spatiotemporal scales. We provided new knowledge on the comparative trophic behaviour of these species, defined as opportunistic in previous investigations. For that purpose we applied a variety of statistical methods to an extensive dataset of 27,188 non-empty stomachs. We defined the spatial organization of the forage fauna of these predators and documented changes in prey composition according to predators' size and spatiotemporal features of environment. Our results highligh the key role played by the dissolved oxygen. We also deciphered an important paradox on the jumbo squid diet: why do they hardly forage on the huge anchovy (Engraulis ringens) biomass distributed of coastal Peru? We showed that the shallow oxygen minimum zone present off coastal Peru could hamper the co-occurrence of jumbo squids and anchovies. In addition, we proposed a conceptual model on jumbo squid trophic ecology including the ontogenetic cycle, oxygen and prey availability. Moreover we showed that the trophic behaviour of jack mackerel and chub mackerel is adapted to forage on more accessible species such as for example the squat lobster Pleurocondes monodon and Zoea larvae. Besides, both predators present a trophic overlap. But jack mackerel was not as voracious as chub mackerel, contradictorily to what was observed by others authors. Fish diet presented a high spatiotemporal variability, and the shelf break appeared as a strong biogeographical frontier. Diet composition of our fish predators was not necessarily a consistent indicator of changes in prey biomass. El Niño events had a weak effect on the stomach fullness and diet composition of chub mackerel and jack mackerel. Moreover, decadal changes in diet diversity challenged the classic paradigm of positive correlation between species richness and temperature. Finally, the global patterns that we described in this work, illustrated the opportunistic foraging behaviour, life strategies and the high degree of plasticity of these species. Such behaviour allows adaptation to changes in the environment
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Zhang, Fei. "On the Variability of the Wind Stress at the Air-Sea Interface." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_dissertations/191.
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This dissertation investigates wind-wave-current interaction, wave breaking detection and the analysis of breaking characteristics at the air-sea interface. In-situ data measured during the Shoaling Waves Experiment (SHOWEX) and Baltic Sea Swell Experiment (BASE) are applied in the studies and analysis. Wind, wind stress and wave data were obtained from several Air Sea Interaction Spar (ASIS) buoys. Surface currents were measured by a High-Frequency Ocean Surface Current Radar. Two distinct types of wave-current-wind interaction were observed in the presence of a strong along-coast current. First, the horizontal current shear resulted in wind-sea waves shifting away from the wind direction. This motion resulted in a steering of the stress away from the mean wind direction. Second, short wind waves on a uniform current are shifted to the current direction, and the wind stress is steered toward the current direction by the short waves. The wind stress veering has been confirmed by data from the SeaWind scatterometer on board the QuikSCAT satellite. This finding is in agreement with the results from some recent studies. The present study also describes an experimental investigation of breaking wave detection by ASIS buoys. A method, developed from the laboratory, and using local wave parameters to provide a detailed description of breaking, is applied to wave data from ASIS buoys. One the basis of these data, the relation between breaking probability and wind speed shows characteristics similar to those from several field experiments with different conditions. Furthermore, additional parameters, wave age and wave steepness, are also shown to affect the breaking probability during our in-situ measurements. Upper ocean shear, which can modulate wave breaking as predicted by both theory and laboratory work, are also observed to change the breaking properties. This characteristic is rarely reported by in-situ experiment.
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Baker-Yeboah, Sheekela. "Sea surface height variability and the structure of eddies in the South Atlantic Cape Basin /." View online ; access limited to URI, 2008. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3314440.
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Artana, Camila. "Revisiting the Malvinas Current." Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS546.pdf.
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Bien que le Courant des Malouines (CM) soit le principal soutien de la productivité élevée qui caractérise l’Atlantique Sud-Ouest il reste encore peu documenté. Cette thèse combine des données in situ et satellitaires et des sorties de modèles opérationnels, pour étudier le CM. Le CM est une émanation du courant Antarctique Circumpolaire (ACC). Il s’écoule vers le nord jusqu’à 38°S puis il retourne vers le sud formant le Courant de Retour des Malouines (CRM). Nous montrons que l’énergie turbulente de l’ACC est filtrée sur le plateau des Malouines (55°S-48°S). Nous avons découvert l'occurrence d’évènements de blocage à 48S qui coupent le CM de sa source l’ACC. Le CM devient alors le bord ouest d’une grande cellule de recirculation cyclonique. Nous avons montré que les positions des fronts du système du CM (Front Polaire, Front Subantarctique et Front du Brésil) peuvent être suivies en définissant des critères sur la densité potentielle et la hauteur de l’eau. Des eaux du sud du front polaire (FP) sont injectées dans le CM (évènements d'alimentation) et recirculent entre le CM et le CRM. Les caractéristiques des eaux de la recirculation varient dans le temps en fonction des évènements d’alimentation et de blocage. Une série temporelle de 24 ans du transport du CM à 41°S a été construite à partir de données de mouillages et d’altimétrie satellitale. Les maxima et minima du transport sont liés à des perturbations de la circulation en provenance du Bassin Argentin (et non de l’ACC): les maxima sont dus à des tourbillons détachés du FP et les minima à des anomalies anticycloniques provenant du courant de BrésilAlthough the Malvinas Current (MC) plays a key role over the Patagonian shelf in sustaining an extremely rich ecosystem it remains rather undocumented. In this thesis, we combined in situ, satellite data, and operational model outputs to study the MC. The MC is an offshoot of the Antarctic Circumpolar Current (ACC). It flows northward up to 38°S where it turns southward forming the Malvinas Return Flow (MRF). We show that a substantial portion of the mesoscale activity from the ACC is dissipated over the Malvinas Plateau. We discovered the occurrence of recurrent blocking events cutting the MC from its source, the ACC. However, the MC does not collapse as a recirculation cell is established. Criteria in potential density and dynamic topography were defined to study the MC system fronts (Polar Front, Subantarctic Front and Brazil Current Front). Waters from the South of the Polar Front (PF) are recurrently injected into the MC as pulses or feeding events. Polar waters accumulate in the recirculation region between the MC and the MRF. Variations in the water characteristics of the recirculation region are consistent with changes in the occurrence of blocking and feeding events. Combining mooring and satellite altimetric data, a 24-year long time series of the MC transport at 41 ° S was constructed. Maxima and minima of the Malvinas current transport at 41 ° S are not associated with the ACC, rather with eddies coming from the Argentine Basin. Transport maxima appear to be related with cyclonic eddied detached from the Polar Front and transport minima with large anticyclonic anomalies from the Brazil Current
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Hüttl, Sabine [Verfasser]. "Mechanisms of near-surface current and upwelling variability in the tropical Atlantic / Sabine Hüttl." Kiel : Universitätsbibliothek Kiel, 2010. http://d-nb.info/1019952407/34.
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Legaard, Kasey. "Temporal Variability of Satellite-Derived Chlorophyll and Sea Suface Temperature in the California Current." Fogler Library, University of Maine, 2004. http://www.library.umaine.edu/theses/pdf/LegaardK2004.pdf.
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Fadida, Yotam. "An altimetry based examination of the path and variability of the Agulhas Return Current." Master's thesis, Faculty of Science, 2018. http://hdl.handle.net/11427/30055.
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As a result of climate change, partially driven by anthropogenic activity, strengthening wind stress over the worlds oceans is yielding a western boundary intensification and pole-ward shift of oceanic currents (Yang, 2016). Shifting wind regimes and perturbations in neighboring currents have been associated with variations in the flow path of western boundary currents (WBC) and their extensions (Talley, 2011; Combes and Matano, 2014; Nakamura and Kazmin 2003). WBCs, typically characterised by fast flowing and warm currents, are key regions of heat and salt transport as well as for oceanic carbon uptake, air-sea heat flux and nutrient transport, thus positional shifts may have far-reaching implications (Gray and Palter, 2017). While meridional trends (latitudinal migrations) have been observed in analogous WBCs and their extensions, no long-term investigation (decadal) into the flow path and position of the Agulhas Return Current (ARC) has been carried out. Now, with over 25 years of altimetric, satellite remote observation data available, a better understanding of the flow path, seasonal cycle, meridional trends and eddy kinetic energy (EKE) of the ARC is possible. Here we provide a detailed description of the flow path of the ARC together with several mechanisms that may be contributing to the current’s apparent stability. In addition we demonstrate that the documented western boundary intensification and pole-ward shift may be manifesting itself in two ways in the ARC, an increase in regional EKE and a southward trend found mainly in the flow-path of the eastern section of the ARC. Our results show a strong link between the EKE of the region and the Subtropical Indian Ocean Dipole, both of which are associated with the Southern Annular Mode (SAM), illustrating the effects that southward shifts in the subtropical high pressure system have on regional and mesoscale climate modes. The combination of a stable, topographically forced flow path with observed EKE increases, demonstrate the effects of wind stress intensification on a region highly influenced by its bathymetry. Further research into the effects of enhanced eddy activity is necessary, as it has been shown to affect regional primary production (Falkowski, 1991; Oschlies, 1998) and air-sea interactions, thus having potential ramifications for regional aquaculture, weather and fisheries, as well as calculations/models concerned with heat-flux and carbon exchange.
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Flexas, Sbert Maria del Mar. "Mesoscale variability of the northern current in the gulf of lions and the role of bottom topography." Doctoral thesis, Universitat Politècnica de Catalunya, 2003. http://hdl.handle.net/10803/6386.
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The Northern Current flows cyclonically contouring the continental slope in the NW Mediterranean. At the entrance of the Gulf of Lions this current is about 20 -- 30 km wide and flows along the deepest half of the continental slope, i.e. over the 1000 to 2000 m isobaths approximately. Surface speeds are of 30 -- 50 cm s^{-1}. In the MATER HFF experiment (March -- May 1997) mesoscale variability of the Northern Current is observed from current meter records, SST images and hydrographic data. The HFF experimental box is 20 x 40 km, covering the upper half of the slope (i.e. covering from 250 m to 1250 m depth isobaths). Current meter and satellite data show that the site is embedded in a region of significant Northern Current meandering and eddy activity. From SST images, meander wavelengths are estimated larger than 60 km, embracing smaller structures. These flow patterns affect upper-layer waters down to at least 650 m depth. Current meter data distinguish two narrow energetic bands centred at 3.5 days and 7.5 days, respectively, in agreement with previous studies.Baroclinic instability is viewed as a possible mechanism to explain the generation of the Northern Current meanders. The analytical model of Tang (1975) predicts the development of unstable waves of wavelength (> 60 km) and periods compatible with the 7.5 day band recorded with current meter devices. The higher frequency band of 3.5 days is out of the frequency range predicted by the classical baroclinic instability theory and it is discussed as a restriction of quasi-geostrophic theory.
Barotropic instability is studied using a laboratory model of a -westward' jet flowing over the lower half of the continental slope, which considers dynamic similarity with the Northern Current. The laboratory model is cross-validated with a corresponding numerical model. Jet instabilities of currents similar to the Northern Current (i.e. westward jets) occur at the edges of the jet, showing a clear meandering tendency over the mid-slope. Westward currents of Ro = 0.1 -- 0.2 develop instabilities of wavelengths (50 -- 75 km) similar to those observed from SST images, with periods (3.3 -- 3.8 days) compatible with the 3.5 days period band recorded with HFFE current meters.
The laboratory and numerical experiments have reproduced westward jets (as the Northern Current), but also eastward jets, in order to have a full approach to better understand the role of the bottom topography on barotropic instabilities. The slope current instabilities are successfully explained by the Marcus and Lee theory (1998) of jets on a beta plane. This theory is valid for westward flows with Ro > 0.1 and for eastward flows with Ro > 0.2 (jets of the so-called Regime II flows in this thesis), and it states that the instabilities of each shear layer of the barotropic jet take the appearance of a Kelvin-Helmholtz-like pattern, associated with a Rossby wave (of topographic origin in our case). According to this theory, the differences between eastward and westward jets rely on the disposition of the Rossby waves --at the centre of the current in eastward flows and at the edges of the jet in westward currents. Jets over a sloping bottom with small Rossby numbers (Ro < 0.1 for westward jets; Ro < 0.2 for eastward jets) show a flow pattern (the so-called Regime I in this thesis) that has common characteristics for eastward and westward flows. In these -small'-Ro flows, Kelvin-Helmholtz-like instabilities dominate, whereas Rossby waves are too weak to produce any major difference between jets flowing in eastward or westward direction. This occurs when the topographic influence, assumed proportional to the Ro number of the jet, is small.
The differences between eastward and westward slope currents observed in this work (and similar observations of jets on a beta-plane from previous works) are explained in this thesis by a simple scheme based on conservation of potential vorticity, considering there are two main components in balance: the shear-induced vorticity and the topographically induced vorticity. The signs of these two components are determined by the relative direction of the flow with respect to the inclination of the bottom topography. Once the critical Rossby number is overpassed so that the topographic effects are important (Ro > 0.1 for westward jets; Ro > 0.2 for eastward jets), conservation of potential vorticity tends to enhance vortices at the centre of eastward jets --eastward jets show meandering at the jet core. In westward jets, potential vorticity conservation is responsible of enhancing vortices at each edge of the jet. Thus, westward jets (as the Northern Current) are broad and meandering occurs at the jet edges.
In Ro > 0.1 westward flows (i.e. Regime II westward jets) a topographic Rossby wave appears over the shelf break. This result is likely observed because of the specific topography used in this work --a continental slope and a continental shelf separated by a shelf break, producing a strong change in ambient potential vorticity. Numerical simulations reveal that this Rossby wave is triggered by the slope current. This topographic Rossby wave is a robust pattern, since it is independent of the position of the current over the slope, the shape of the velocity shear profile of the jet, and the jet width. Although this type of wave could not be inferred from the HFFE field data, it could be a focus of study in further field experiments. It also needs further analytical consideration.
The general conclusion extracted from this thesis that tries to explain the mesoscale variability associated to the Northern Current is that both baroclinic and barotropic instability could explain part of the oceanic observations. As a consequence, mixed barotropic-baroclinic instability (which occurs at wavelengths which are between those corresponding to pure barotropic and pure baroclinic instability) is thought to play an important role on the observed mesoscale variability. The resulting wavelength would depend on the relative strength of both mechanisms.
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Field, David B. "Planktonic foraminifera in the California current : vertical distributions, decadal climate variability and 20th century warming /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3142453.
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Panitz, Sina. "Pliocene vegetation and climate of Arctic Norway and the variability of the Norwegian Atlantic current." Thesis, Northumbria University, 2016. http://nrl.northumbria.ac.uk/36131/.
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The Pliocene Epoch (5.33–2.59 Ma) is characterised by climatic conditions similar to those predicted for 2100, with enhanced warming in the (sub-)Arctic. The climate evolution at high latitudes is not well understood due to the sparsity of time-continuous palaeoenvironmental records. This study provides new records of Pliocene vegetation changes in Arctic Norway and the variability of the Norwegian Atlantic Current based on analyses of terrestrial and marine palynomorphs from ODP Site 642 (Norwegian Sea, 67°N) to assess climate variability and identify different scale forcing mechanisms. The Piacenzian pollen record (3.60–3.14 Ma) shows vegetation changes between cool temperate and boreal forests during warmer-than-present and similar-to-present climate phases, respectively, implying shifts of the northern deciduous/mixed forest limit of 4–8° latitude. During warm phases, warmest month temperatures were 8–14°C higher than present. The development of peatlands during cooler phases may have amplified the cooling through CO2-drawdown and positive vegetation-snow feedbacks. The high regional and hemispheric-wide climate variability highlights the importance of well-dated, high-resolution records for regional to global palaeoenvironmental reconstructions and data-model comparisons. Long-term Pliocene vegetation changes (5.03–3.14 Ma) reveal a continuous decline of thermophilic elements over successive warm phases, supporting the notion of long-term climate cooling caused by decreasing CO2 concentrations. This cooling is superimposed on shifts between cool temperate and boreal climate phases on multi-millennial timescales. Minima in eccentricity (400-ka), together with low-amplitude obliquity/precession cycles are associated with the development of boreal conditions. At 4.56 Ma, a marked decline in pollen influx suggests atmospheric circulation changes in response to the shoaling of the Central American Seaway, a hypothesis supported by model results. Subsequently, changes in northward heat transport via the North Atlantic Current strongly affected vegetation changes. The Pliocene climate evolution represents the later part of late Neogene cooling instead of a reversal of that trend. Dinoflagellate cyst assemblage changes (3.320–3.137 Ma) indicate variations in Atlantic and Arctic water influence, corresponding to cool temperate and boreal terrestrial climatic conditions in Arctic Norway, respectively. These records emphasise a high climate variability on glacial-interglacial timescales and linkage of both marine and terrestrial environmental changes.
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Rykova, Tatiana A. "The seasonal and interannual variability of the West Greenland current system in the Labrador Sea." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59755.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010."June 2010." Cataloged from PDF version of thesis.
Includes bibliographical references (p. 151-159).
The Labrador Sea, as one of a few places of deep water formation, plays an important role in the Meridional Overturning Circulation. While the interior of the Labrador Sea, where the deepest convection takes place, is known to experience variability on time scales ranging from days to decades, little is known about the variability of the other components of the Labrador Sea circulation - the boundary current system and the eddies that connect it with the interior. Using various types of in situ data combined with the surface flux and satellite altimetry data products, I studied the variability of both the boundary current system and the eddies on different time scales as well as their influence on the post-convective re-stratification of the Labrador Sea interior. The analysis presented in the thesis supports the result of the previous theoretical studies that argue that lateral fluxes, driven by the boundary current/interior gradients, play an important role in the post-convective restratification of the Labrador Sea. I found that both components of the boundary current, the surface West Greenland Current and the subsurface Irminger Current, have a strong seasonal cycle. In the spring both the West Greenland and Irminger Currents are colder and fresher than in the fall. However, the West Greenland Current is faster and thicker in the spring while the Irminger Current is the fastest and thickest in the fall. My analysis suggests that the observed seasonal changes in the velocity are primarily due to the baroclinic component of the current while the barotropic component remains nearly unchanged. The Subpolar Gyre, and the Labrador Sea in particular, have experienced a decline in the circulation accompanied by the warming of the water column over the last decades. I found that a similar trend is seen in the West Greenland Current system which slowed down from 1992 to 2004, primarily due to a decrease in the barotropic flow. At the same time, the subsurface Irminger Current has become warmer, saltier, and lighter, something that is also reflected in the properties of the eddies. Two years exhibited pronounced anomalies: in 1997 and 2003 the velocity, temperature and salinity of the Irminger Current abruptly increase with respect to the overall trend. Finally, I discuss the impacts of the boundary current changes on the lateral fluxes that are responsible for the restratification of the Labrador Sea and the properties of the interior.
by Tatiana Rykova.
Ph.D.
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Backeberg, Bjorn Christoph. "Modelling the mesoscale variability in the greater Agulhas Current system using hybrid coordinate Ocean model." Doctoral thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/6458.
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The ocean circulation dynamics in the greater Agulhas Current system are dominated by mesoscale variability, which is highly non-linear, and therefore difficult to measure and simulate accurately. Moreover, the shedding of Agulhas rings from the retroflection south of Africa, which is the dominant mechanism by which warm and saline water flows from the Indian into the Atlantic Ocean, is thought to be a crucial component of the thermohaline circulation. With the goal of providing an accurate simulation of the greater Agulhas Current system, and in particular its mesoscale variability, a high resolution Hybrid Coordinate Ocean Model is set up in a nested configuration. In two 11 year simulation experiments, the effect of a higher order momentum advection scheme on the simulated ocean dynamics is tested and evaluated against available satellite observations and in-situ measurements. Quantitative analyses and model validation methods are developed to objectively evaluate the simulation experiments. The resultant skewness analyses and spatial variograms are objective measures for assessing the model simulation and additionally provide new insights on the mesoscale dynamics of the greater Agulhas Current system. A 4th order momentum advection scheme is shown to significantly improve the simulation of the region, in particular the dynamics of the southern Agulhas Current and the retroflection are greatly improved. From the analyses of the two model simulations in conjunction with satellite observations and in-situ measurements, it is found that the Indo-Atlantic inter-ocean exchange, and the shedding of Agulhas rings from the retroflection, is sensitive to the strength of the Agulhas Current, which in turn is influenced by the flow dynamics in the Mozambique Channel and south of Madagascar. Mesoscale eddies drifting from these source regions to the Agulhas Current play an important role, and the connection between the Agulhas Current and the respective source regions provides a link to large-scale variability in the Indian Ocean, which in turn is related to interannual modes of variability such as the Indian Ocean Dipole and El NiÑo Southern Oscillation.
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Rischmiller, Frederick William. "Variability of the California Current System off Point Sur, California from April 1988 to December 1990." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA278579.
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Thesis (M.S. in Physical Oceanography) Naval Postgraduate School, December 1993.Thesis advisor(s): Newell Garfield ; Curtis A. Collins. "December 1993." Bibliography: p. 155-157. Also available online.
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Kovac, Urban. "3D drift diffusion and 3D Monte Carlo simulation of on-current variability due to random dopants." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2309/.
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In this work Random Discrete Dopant induced on-current variations have been studied using the Glasgow 3D atomistic drift/diffusion simulator and Monte Carlo simulations. A methodology for incorporating quantum corrections into self-consistent atomistic Monte Carlo simulations via the density gradient effective potential is presented. Quantum corrections based on the density gradient formalism are used to simultaneously capture quantum confinement effects. The quantum corrections not only capture charge confinement effects, but accurately represent the electron impurity interaction used in previous \textit{ab initio} atomistic MC simulations, showing agreement with bulk mobility simulation. The effect of quantum corrected transport variation in statistical atomistic MC simulation is then investigated using a series of realistic scaled devices nMOSFETs transistors with channel lengths 35 nm, 25 nm, 18nm, 13 nm and 9 nm. Such simulations result in an increased drain current variability when compared with drift diffusion simulation. The comprehensive statistical analysis of drain current variations is presented separately for each scaled transistor. The investigation has shown increased current variation compared with quantum corrected drift diffusion simulation and with previous classical MC results. Furthermore, it has been studied consistently the impact of transport variability due to scattering from random discrete dopants on the on-current variability in realistic nano CMOS transistors. For the first time, a hierarchic simulation strategy to accurately transfer the increased on-current variability obtained from the ‘ab initio’ MC simulations to DD simulations is subsequently presented. The MC corrected DD simulations are used to produce target $I_D-V_G$ characteristics from which statistical compact models are extracted for use in preliminary design kits at the early stage of new technology development. The impact of transport variability on the accuracy of delay simulation are investigated in detail. Accurate compact models extraction methodology transferring results from accurate physical variability simulation into statistical compact models suitable for statistical circuit simulation is presented. In order to examine te size of this effect on circuits Monte Carlo SPICE simulations of inverter were carried out for 100 samples.
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Wolf, Shaye G. "Population consequences of current and predicted ocean climate variability for the seabird Cassin's auklet Ptychoramphus aleuticus /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2007. http://uclibs.org/PID/11984.
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Almeida, Helio Miguel dos Reis. "Mesoscale variability of the Brazil Current in the Santos Bight: is it locally or remotely forced?" Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-26032018-143335/.
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The Brazil Current (BC) is possibly one of the least studied western boundary currents (WBCs) in the world ocean. Its unique vertical structure makes this a different WBC in terms of velocity and transport. Although significant progress has been made over the last decade, the BC system variability within the Santos Bight (SB, 23°S-28°S) is very poorly understood despite its strategic role for Brazil in terms of energy. The BC thickens and changes its vertical structure and dynamical modal composition as it crosses the SB. As it enters the bight by trying to contour Cape Frio (Cf, 23°S), the BC is about 500 m deep. As the current leaves the bight south of Cape Santa Marta (CSM, 28°S) it is 1300 m. These differences in thickness and accompanying velocity vertical shear are due to the impinging branch of the intermediate South Equatorial Current (SEC) generating the so called Santos Bifurcation (SBi). We here investigate the subinertial variability of the BC system within the SB primarily using satellite altimetry data and some traditional spectral analysis techniques. We also analyzed quasi-synoptic observations of an oceanographic cruise, which was part of the IOUSP-PETROBRAS CERES Experiment. We identified that there are different phenomena occurring to the north and to the south of the bifurcation and this might be caused by the SBi feature itself and/or the consequential change in the BC vertical structure downstream. North of the SBi, we detected oscillations with period of 92 days and a wavelength of 490 km and which represent about a fifth of the BC variability at 25°S. The 92-day oscillations are nonlinear vorticity waves, which are originated to the east of 35°W and propagate zonally towards the BC axis. These waves then perturb the current exciting oscillatory motions of the same period and which propagate downstream. South of the SBi axis (~28°S), we identified two different maxima in the ω - κ spectrum. They correspond to oscillations with periods (wavelengths) of 68 and 148 days (397 km and 790 km). The longer wave is also a baroclinic first-mode nonlinear vorticity waves propagating with westward phase speed of the nondispersive planetary Rossby waves of same period. They are originated in the ocean interior and we were able to track its signal as far as 5°W. The 68-day waves has its existence limited to vicinities of the BC. Phase speeds have approximately the BC axis orientation and they can only be clearly detected between ~27°S and ~32°S. This propagating signal accounts with a variance of ~21% on the BC axis. Quasi-synoptic observations allowed the mapping of a anticyclone and a cyclone of such waves. They seem to have modal composition very similar to the BC itself, which might provide additional evidence of local origin.A Corrente do Brasil (CB) é provavelmente a Corrente de Contorno Oeste (CCO) menos estudada dos oceanos mundiais. A sua estrutura vertical única es faz dela uma CCO diferente em termos de velocidade e transporte. Apesar dos avanços significativos na última década, a variabilidade da CB na Bacia de Santos (BS, 23°S-28°S) ainda é pouco conhecida, apesar do papel estratégico da região na matriz energética brasileira. A CB se espessa mudando a sua estrutura vertical e muda sua estrutura dinâmica no domínio da BS. Na região de Cabo Frio (23°S) a corrente tem cerca de 500 m de profundidade. Ao sair da BS na região do Cabo de Santa Marta (28°S) a corrente se estende até cerca de 1300 m. Estas variações na espessura da corrente e consequente diferença no cisalhamento vertical de velocidade ocorrem devido à presença da Corrente Sul Equatorial em nível intermediário na região gerando a Bifurcação de Santos (BiS). Neste trabalho investigamos a variabilidade subinercial da CB na Bacia de Santos usando primeiramente dado alimétrico e um conjunto de análise espectral. Foram depois estudados fenômenos geradores dessa variabilidade com dados quasi-sinóticos do um cruzeiro oceanográfico CERES V do conjunto IOUSP-PETROBRAS. Foram identificados fenômenos diferentes no norte e sul da Bifurcação de Santos e esta diferença é provavelmente devido à presença da bifurcação ou à mudança que esta causa na estrutura da CB. Ao norte da BiS foi identificada uma oscilação com período de 92 dias e comprimento de onda de 490 km explicando um quinto da variabilidade da CB em 25°S. A oscilação de 92 dias está relacionada com ondas de vorticidade não lineares originadas a leste da corrente em ~35°W e se propagam zonalmente até ao eixo da corrente. Estas ondas perturbam a corrente originando oscilações com mesmo período e que propagam ao longo do eixo da corrente. Ao sul da BiS (~27°S) foram identificados dois máximos no espectro κ - ω. Os máximos correspondem a oscilações com período (comprimento de onda) de 68 e 148 dias (397 e 790 km). A onda com maior comprimento de onda é também uma onda de vorticidade de primeiro modo baroclínico não linear propagando para oeste com velocidade de fase de ondas de Rossby não dispersivas. Estas ondas são originadas no interior da bacia oceânica e seu sinal foi identificado chegando até 5°W. A onda de 68 dias existe apenas no domínio da CB. Esta onda propaga fase num eixo aproximadamente paralelo à CB e são detadas de forma clara apenas entre ~27°S e ~32°S. Esta onda explica uma variância da CB de ~21% ao longo do seu eixo. Observações quasi-sinóticas permitiram mapear um anticiclone e um ciclone associado a essa onda. Os vórtices aparentam uma estrutura modal muito semelhante à da corrente.
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Sorensen, Hilarie. "Population Dynamics and Variability of Two Gelatinous Zooplankters (Aequorea and Pyrosoma atlanticum) in the Northern California Current." Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24236.
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This research focused on population dynamics of two gelatinous zooplankters (Aequorea & Pyrosoma atlanticum) in the northern California Current to assess their relationship to environmental conditions and role in the pelagic ecosystem. Data collected since 1999 showed seasonal and interannual fluctuations in the abundance and distribution of Aequorea in the NCC, with a positive correlation with sea surface temperature and salinity. Pyrosoma atlanticum, which are typically found in tropical waters, have only been observed in high abundances in the NCC since 2014 and their role in the pelagic ecosystem is not well understood. Pyrosome abundance related to in situ environmental variables showed a positive correlation with warmer SST. We also used fatty acids as trophic markers to better understand pyrosome trophic ecology in the NCC. FA biomarkers suggest that pyrosomes have a broad phytoplankton diet, which may indicate an ability to inhabit warmer, lower nutrient zones.2020-01-11
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Malin, Melissa L. "Teleconnection pattern impacts on intra-seasonal climate variability in United States winters." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 244 p, 2009. http://proquest.umi.com/pqdweb?did=1891555391&sid=3&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Holub, Anna, and Jie Liu. "Recognizing Combustion Variability for Control of Gasoline Engine Exhaust Gas Recirculation using Information from the Ion Current." Thesis, Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-235.
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The ion current measured from the spark plug in a spark ignited combustion engine is used
as basis for analysis and control of the combustion variability caused by exhaust gas
recirculation. Methods for extraction of in-cylinder pressure information from the ion
current are analyzed in terms of reliability and processing efficiency. A model for the
recognition of combustion variability using this information is selected and tested on both
simulated and car data.
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Weigel, Alan M. "Mesoscale variability in the west Spitsbergen Current and adjacent waters in Fram Strait: by Alan M. Weigel." Thesis, Monterey, California. Naval Postgraduate School, 1987. http://hdl.handle.net/10945/22353.
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Roberts, William Henry Gordon. "An investigation into the causes for the reduction in the variability of the El Niño-Southern Oscillation in the early Holocene in a global climate model /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10033.
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Xu, Zhonghua. "Study of Geomagnetic Disturbances and Ring Current Variability During Storm and Quiet Times Using Wavelet Analysis and Ground-based Magnetic Data from Multiple Stations." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/984.
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The magnetosphere-ionosphere contains a number of current systems. These currents vary on a wide range of spatial and temporal scales and physically couple with each other. To study the complicated behaviors of these coupled current systems, the ground-based magnetometer has been a useful tool, but the recorded magnetometer data are always multi-scaled and intermittent due to the nature of these current systems. To distinguish these geomagnetic effects with multiple temporal and frequency scales, the wavelet analysis technique is especially suitable because of its special abilities of presenting information in both temporal and frequency domains. In this dissertation, the geomagnetic disturbances and the ring current variability during storm and quiet times are studied by using wavelet analysis and ground-based magnetic data from multiple stations. The first part of this dis- sertation investigates the strengths of applying the wavelet procedure to geomagnetic data for ring current study during storm and quiet periods. The second part of this dissertation characterizes the geomagnetic effects caused by symmetric and asymmetric components of ring currents during storm and quiet times by applying wavelet analysis to geomagnetic data from multiple stations. The third part of this dissertation studies the spatial variabil- ity of the symmetric ring current by applying the wavelet analysis technique to multiple components of magnetic data from multiple stations. The results show the unique strengths of the wavelet method allow us to quantitatively distinguish the geomagnetic effects on ring current variations from other M-I current systems. The unique strengths of wavelet method also allow us to separate the magnetic effects of the symmetric ring current from those caused by the asymmetric ring current. Quantitative information of the spatial variability of the ring currents is essential for understanding the dynamics of the ring currents, as well as the magnetic storm processes. The techniques developed in this dissertation have potential values as space weather monitoring tools for satellite controls, power grids, com- munication systems, oil pipelines, and other high-tech systems that are vulnerable to the negative impacts of disruptive geomagnetic events.
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Lenn, Yueng Djern. "Observations of Antarctic Circumpolar Current dynamics in the Drake Passage and small-scale variability near the Antarctic Peninsula." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3230035.
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Thesis (Ph. D.)--University of California, San Diego, 2006.Title from first page of PDF file (viewed November 17, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 126-136).
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Andersson, Camilla. "Air pollution dependency on climate variability and source region : past, current and future air pollution scenarios over Europe /." Stockholm : Department of applied environmental science, Stockholm University, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-25947.
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Ishimura, Gakushi. "Transboundary management of a fish stock under climate variability : the case of Pacific sardine in the California current ecosystem." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23246.
Full textAbstract:
The time variant/asymmetric distribution of a fish stock caused by ocean climate variability is one of the challenges that must be overcome to establish cooperative management of a transboundary fish stock. Pacific sardine (Sardinops sagax) exhibits extreme decadal variability in its abundance and geographic distribution that corresponds to water temperature regime shifts within the California Current Ecosystem. It is a transboundary fish stock and targeted by Mexican, American and Canadian fisheries, and the three countries do not currently have a cooperative management arrangement. This thesis explores the economic and conservation consequences of non-cooperative management, and the potential benefits of full/partial cooperative management of Pacific sardine, and studies the stability of cooperative management under ocean climate variability. The core of the thesis is presented in Chapters 2-4, with an introduction given in Chapter 1 and a conclusion in Chapter 5. Appendix A and B provide background information on Pacific sardine and the Pacific sardine fishery, respectively.
Chapter 2 develops a three-agent bioeconomic framework to investigate the impact of ocean climate variability on stock abundance and geographic distribution. A game theoretic analysis was conducted to evaluate the conservation and economic benefits of various management strategies. The results show that under a regime of ocean climate variability, a country having a dominate share of the resource within its waters cannot achieve effective unilateral conservation for optimal economic benefits due to the actions of free-riders.
Chapter 3 conducts simulations to evaluate the stability of full and partial cooperative management of Pacific sardine under various climate variability scenarios. The results show that in all scenarios, ocean climate variability is an obstacle to the formation of stable, fully-cooperative management of Pacific sardine fisheries as operated by the three countries.
Chapter 4 estimates the cost of delaying cooperative management of this fishery, and how costs are incurred due to such delays. The results suggest that the cost of delaying cooperative management is significant for a country having a dominant share, while countries that have minor shares gain economic benefits from delaying cooperative management.
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Thorpe, Sally Elaine. "Variability of the Southern Antarctic circumpolar current in the Scotia Sea and its implications for transport to South Georgia." Thesis, University of East Anglia, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368389.
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Rykaczewski, Ryan Ross. "Influence of oceanographic variability on the planktonic prey and growth of sardine and anchovy in the California current ecosystem." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3354961.
Full textAbstract:
Thesis (Ph. D.)--University of California, San Diego, 2009.Title from first page of PDF file (viewed June 16, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Peña-Molino, Beatriz. "Variability in the North Atlantic Deep Western Boundary Current : upstream causes and downstream effects as observed at Line W." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62495.
Full textAbstract:
Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 165-174).
The variability in the DWBC, its connection to the forcing in the northern North Atlantic and interaction with the Gulf Stream were explored from a combination of remote sensing and in-situ measurements in the western North Atlantic. Using satellite altimetry and Sea Surface Temperature (SST) we found evidence of the relation between changes in the Gulf Stream path and the variability in the temperature and velocity fields in the Slope Water. This relation was such that southward shifts of the main axis of the Gulf Stream were preceded by cold temperature anomalies and intensification of the southwestward flow. The analysis of 5.5 years of moored CTD and horizontal velocity data in the DWBC at 69 0W recorded during the period 2002-2008, showed that the variability along the DWBC is linked to changes in the dense water formation regions. The evolution of potential vorticity (PV) at the mooring site, characterized by a transition from deep to upper Labrador Sea Water (LSW), was similar to that observed in the Labrador Sea 6 to 9 years earlier, and imply spreading rates for the LSW that varied over time from 1.5 to 2.5cm/s. The time dependence of the spreading rates was in good agreement with changes in the strength of the DWBC at the mooring site. The evolution of the DWBC transport was explored in more detail from a 5- element moored array, also at 69'W. The results, for the period of 2004-2008, were consistent with the single mooring analysis. The variability measured from the array showed that upper, intermediate and deep water mass layers expand and contract at each other's expense, leading to alternating positive and negative PV anomalies at the upper-LSW, deep-LSW and Overflow Water (OW). Larger DWBC transports were associated with enhanced presence of recently ventilated upper-LSW and OW, rather than deep-LSW. The relative contribution of the different water masses to the observed circulation was investigated by inverting individual PV anomalies isolated from the observations. We found that changes in the depth-integrated circulation were mostly driven by changes in the OW.
by Beatriz Peña-Molino.
Ph.D.
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Březina, Jiří. "Časový vývoj metrologických charakteristik elektromagnetických indukčních měřidel bodových rychlostí." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2019. http://www.nusl.cz/ntk/nusl-392151.
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This experimental diploma thesis investigates the changes in the metrological characteristics of the electromagnetic current meter of velocity. The theoretical part of the thesis includes a brief summary of technical and metrological characteristics of these types of devices. In addition, it describes the tested device, the test track, and the measurement procedure, which consists of two variants: long-term monitoring with a relatively regular monthly measurement interval and short-term monitoring with a regular daily measurement interval. The evaluation of the experimental work focuses on the repeatability and variability of the displayed point speed values and their stability over time. Furthermore, the parameters reported by the meter during long-term and short-term monitoring are compared to each other. The results are also compared with similar experiments.
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Domingues, Catia Motta, and Catia Domingues@csiro au. "Kinematics and Heat Budget of the Leeuwin Current." Flinders University. SOCPES, 2006. http://catalogue.flinders.edu.au./local/adt/public/adt-SFU20060612.211358.
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This study investigates the upper ocean circulation along the west Australian coast, based
on recent observations (WOCE ICM6, 1994/96) and numerical output from the 1/6 degree Parallel Ocean
Program model (POP11B 1993/97). Particularly, we identify the source regions of the Leeuwin
Current, quantify its mean and seasonal variability in terms of volume, heat and salt transports,
and examine its heat balance (cooling mechanism). This also leads to further understanding of the
regional circulation associated with the Leeuwin Undercurrent, the Eastern Gyral Current and the
southeast Indian Subtropical Gyre.
The tropical and subtropical sources of the Leeuwin Current are understood from an
online numerical particle tracking. Some of the new findings are the Tropical Indian Ocean source
of the Leeuwin Current (in addition to the Indonesian Throughflow/Pacific); the Eastern Gyral
Current as a recirculation of the South Equatorial Current; the subtropical source of the Leeuwin
Current fed by relatively narrow subsurface-intensified eastward jets in the Subtropical Gyre, which
are also a major source for the Subtropical Water (salinity maximum) as observed in the Leeuwin
Undercurrent along the ICM6 section at 22 degrees S.
The ICM6 current meter array reveals a rich vertical current structure near North West
Cape (22 degrees S). The coastal part of the Leeuwin Current has dominant synoptic variability and
occasionally contains large spikes in its transport time series arising from the passage of tropical
cyclones. On the mean, it is weaker and shallower compared to further downstream, and it only
transports Tropical Water, of a variable content. The Leeuwin Undercurrent carries Subtropical
Water, South Indian Central Water and Antarctic Intermediate Water equatorward between
150/250 to 500/750 m. There is a poleward flow just below the undercurrent which advects a
mixed Intermediate Water, partially associated with outflows from the Red Sea and Persian Gulf.
Narrow bottom-intensified currents are also observed.
The 5-year mean model Leeuwin Current is a year-round poleward flow between 22 degrees S and
34 degrees S. It progressively deepens, from 150 to 300 m depth. Latitudinal variations in its volume
transport are a response to lateral inflows/outflows. It has double the transport at 34 degrees S (-2.2 Sv)
compared to at 22 degrees S (-1.2 Sv). These model estimates, however, may underestimate the transport
of the Leeuwin Current by 50%. Along its path, the current becomes cooler (6 degrees C), saltier (0.6 psu)
and denser (2 kg m -3). At seasonal scales, a stronger poleward flow in May-June advects the
warmest and freshest waters along the west Australian coast. This advection is apparently spun up
by the arrival of a poleward Kelvin wave in April, and reinforced by a minimum in the equatorward
wind stress during July.
In the model heat balance, the Leeuwin Current is significantly cooled by the eddy heat
flux divergence (4 degrees C out of 6 degrees C), associated with mechanisms operating at submonthly time scales.
However, exactly which mechanisms it is not yet clear. Air-sea fluxes only account for ~30% of the
cooling and seasonal rectification is negligible. The eddy heat divergence, originating over a narrow
region along the outer edge of the Leeuwin Current, is responsible for a considerable warming of a
vast area of the adjacent ocean interior, which is then associated with strong heat losses to the
atmosphere. The model westward eddy heat flux estimates are considerably larger than those
associated with long lived warm core eddies detaching from the Leeuwin Current and moving
offshore. This suggests that these mesoscale features are not the main mechanism responsible for
the cooling of the Leeuwin Current. We suspect instead that short lived warm core eddies might
play an important role.
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Kopte, Robert [Verfasser]. "The Angola Current in a Tropical Seasonal Upwelling System : Seasonal Variability in Response to Remote Equatorial and Local Forcing / Robert Kopte." Kiel : Universitätsbibliothek Kiel, 2017. http://d-nb.info/1144955181/34.
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