Dissertations / Theses on the topic 'Western boundary current separation'
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Munday, David R. "On the flow separation of western boundary currents." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415521.
Full textKiss, Andrew Elek, and Andrew Kiss@anu edu au. "Dynamics of laboratory models of the wind-driven ocean circulation." The Australian National University. Research School of Earth Sciences, 2001. http://thesis.anu.edu.au./public/adt-ANU20011018.115707.
Full textWaterman, Stephanie N. "Eddy-mean flow interactions in western boundary current jets." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/55330.
Full textIncludes bibliographical references (p. 257-264).
This thesis examines the nature of eddy-mean flow interactions in western boundary current jets and recirculation gyre dynamics from both theoretical and observational perspectives. It includes theoretical studies of eddy-mean flow interactions in idealized configurations relevant to western boundary current jet systems, namely (i) a study of the mechanism by which eddies generated from a localized forcing drive mean recirculation gyres through the process of nonlinear rectification; and (ii) a study of the role of eddies in the downstream evolution of a baroclinic jet subject to mixed instabilities. It also includes an observational analysis to characterize eddy-mean flow interactions in the Kuroshio Extension using data from the downstream location of maximum eddy kinetic energy in the jet. New insights are presented into a rectification mechanism by which eddies drive the recirculation gyres observed in western boundary current systems. Via this mechanism, eddies drive the recirculations by an up-gradient eddy potential vorticity flux inside a localized region of eddy activity. The effectiveness of the process depends on the properties of the energy radiation from the region, which in turn depends on the population of waves excited. In the zonally-evolving western boundary current jet, eddies also act to stabilize the unstable jet through down-gradient potential vorticity fluxes. In this configuration, the role of eddies depends critically on their downstream location relative to where the unstable time-mean jet first becomes stabilized by the eddy activity. The zonal advection of eddy activity from upstream of this location is fundamental to the mechanism permitting the eddies to drive the mean flows.
(cont.) Observational results are presented that provide the first clear evidence of a northern recirculation gyre in the Kuroshio Extension, as well as support for the hypothesis that the recirculations are, at least partially, eddy-driven. Support for the idealized studies' relevance to the oceanic regime is provided both by indications that various model simplifications are appropriate to the observed system, as well as by demonstrated consistencies between model predictions and observational results in the downstream development of time-mean and eddy properties.
by Stephanie N. Waterman.
Ph.D.
Miranda, Juliana Albertoni de. "Dynamics of Brazil Current dipoles: barotropic instabilities and flow-western boundary interactions." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-09022015-095946/.
Full textA presente tese examina a natureza das interações entre jato e contorno e o papel de instabilidades barotrópicas no sistema Corrente do Brasil (CB) quando este ainda se encontra fluindo junto à margem continental oeste. A motivação se deu através da frequente observação de feições bipolares associadas ao escoamento da CB ao sul de Cabo Frio (RJ) e ao largo da Bacia de Santos (entre 22º e 28ºS). Tais observações se devem principalmente a imagens termais de temperatura da superfície do mar, a algumas raras observações \"in situ\" através de dados hidrográficos e medições diretas de velocidade. Assim, o principal foco é na formação de feições bipolares associadas ao fluxo médio, sendo a principal hipótese a de que instabilidade barotrópica é responsável pela formação destes dipolos ao longo da corrente quando esta tem que lidar com variações da topografia. Este estudo tenta abordar os problemas em uma perspectiva semi-teórica, e também através de modelagem numérica em uma abordagem de estudos de processo. Assim, inclui estudos semi-teóricos em configurações idealizadas relevantes para o sistema Corrente do Brasil ao largo de Cabo Frio, considerando a teoria quase-geostrófica como a aproximação apropriada para a dinâmica do sistema que queremos avaliar. Adicionalmente, a modelagem numérica é usada através da construção de cenários idealizados onde simplificamos a física a fim de isolar os processos que queremos investigar. Toda a análise dinâmica partiu de um conjunto de dados que compreendeu o sistema Corrente do Brasil ao largo de Cabo Frio. Validamos a teoria quase-geostrófica que estamos considerando e obtivemos as características cinemáticas do jato. Nas análises dinâmicas, começamos a investigação do problema partindo do cenário mais simples utilizado aqui, onde consideramos um campo de vorticidade potencial discretizado em camadas horizontais em um modelo quase-geostrófico de dinâmica de contornos. O modelo incorporou a presença de uma linha de costa retilínea orientada meridionalmente no contorno oeste. Posteriormente, incluímos mais complexidade no sistema, idealizando diferentes cenários de linha de costa e considerando um campo de vorticidade potencial quase-contínuo em um modelo numérico quase-geostrófico. Finalmente, construímos um cenário ainda mais complexo para a Corrente do Brasil, o qual incorporou a topografia real da região e a estratificação da coluna de água em um modelo numérico de equações primitivas. Dentre as principais conclusões, pudemos comprovar que instabilidade barotrópica pode promover a formação de dipolos. Além disso, variações no contorno podem consequentemente ser gatilhos para gerar perturbações no jato e dipolos se formam. Assim, locais de mudança abrupta de batimetria e orientação de linha de costa são preferidos para a formação de dipolos vorticais. Rua de vórtices e trens de instabilidade também podem se desenvolver à juzante de tais locais como consequência de se perturbar um jato potencialmente barotropicamente instável. Consequentemente, um cisalhamento horizontal é chave para a geração de dipolos vorticais. Um cisalhamento relativamente fraco não permite a formação de tais feições, e em vez disso, vórtices frontais são possivelmente gerados, com a predominância de anticiclones. Apesar de as três diferentes estratégias aplicadas aqui diferirem em termos de configurações dinâmicas e aproximações, estas ainda mantiveram aproximadamente o mesmo regime para a formação de dipolos. Variações na topografia tais como aquelas associadas com mudanças de orientação de costa próximo a Cabo Frio (23ºS) contam com o fato de dipolos vorticais e rua de vórtices serem frequentemente observados dentro da Bacia de Santos.
Deese, Heather E. "Chaotic advection and mixing in a western boundary current-recirculation system : laboratory experiments /." Online version, 2000. http://hdl.handle.net/1912/3036.
Full textIncludes bibliographical references (p. 116-118).
Deese, Heather E. (Heather Elizabeth) 1975. "Chaotic advection and mixing in a western boundary current-recirculation system : laboratory experiments." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/53538.
Full textIncludes bibliographical references (p. 116-118).
I study the exchange between a boundary current and flanking horizontal recirculations in a 'sliced-cylinder' rotating tank laboratory experiment. Two flow configurations are investigated: a single recirculation and a double, figure-8, recirculation. The latter case involves a hyperbolic point, while the former does not. I investigate the stirring and mixing under both steady and unsteady forcing. I quantify the mixing in each case using effective diffusivity, Keff, and a corollary effective length, Leff, as derived by Nakamura (1995, 1996). This approach involves diagnosing the geometric complexity of a tracer field. Geometric complexity is indicative of advective stirring. Because stirring creates high gradients, flows with high advective stirring also have high diffusion, and stronger overall mixing. I calculate effective length from images of dye in the tank and find much higher values of Leff in the unsteady hyperbolic cases than in the other cases. Slight unsteadiness in flows involving hyperbolic points gives rise to a chaotic advection mechanism known as 'lobe dynamics'. These lobes carry fluid in and out of the recirculations, acting as extremely effective stirring mechanisms. I demonstrate the existence of these exchange lobes in the unsteady hyperbolic (figure-8) flow. The velocity field in the tank is calculated utilizing particle image velocimetry (PIV) techniques and a time series U(t) demonstrates the (forced) unsteadiness in the flow. Images of dye in the tank show exchange lobes forming at this same forcing period, and carrying fluid in and out of the recirculation. Based on the results of these experiments, I am able to confirm that, at least in this controlled environment, basic geometry has a profound effect on the mixing effectiveness of a recirculation. I demonstrate radically increased stirring and mixing in the unsteady hyperbolic flow as compared to steady flows and flows without hyperbolic points. Recirculations are ubiquitous in the world ocean; they occur on a variety of scales, in many different configurations, and at all depths. Some of these configurations involve hyperbolic points, while others do not. Chaotic advection via lobe exchange may be an important component of the mixing at multiple locations in the ocean where hyperbolic recirculation geometries exist.
by Heather E. Deese.
S.M.
Stahr, Frederick R. "Transport and bottom boundary layer observations of the North Atlantic deep western boundary current at the Blake Outer Ridge /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/10998.
Full textSILVA, Marcus André. "Seasonal variablity of the heat and mass transport along the western boundary of tropical Atlantic." Universidade Federal de Pernambuco, 2009. https://repositorio.ufpe.br/handle/123456789/8228.
Full textCoordenação de Aperfeiçoamento de Pessoal de Nível Superior
O Atlântico tropical compreendido entre 20ºN e 20ºS apresenta-se hoje como chave para o entendimento das mudanças climáticas na Terra. Duas regiões despertam particular interesse: A banda equatorial do Atlântico onde o sistema de correntes interage com forçantes térmicos superficiais e ressurgência de Ekman, como a área sudoeste do Atlântico tropical (05°S-25°S / 20°W-47°W), onde parte da Corrente Sul Equatorial (CSE) penetra pela borda leste e contribui com muitas das correntes de fronteira oeste ao longo da plataforma continental brasileira. Entretanto, a variabilidade da dinâmica nestas regiões, que se mostra importante por sua contribuição sobre o clima da região nordeste do Brasil, apresenta-se pouco estudada. O presente trabalho investigou estes importantes sistemas do Atlântico tropical utilizando o ROMS (Regional Ocean Model System). A primeira área de estudo compreendida entre 20°S-20°N e 42°W 15°E, com resolução horizontal de 1/6º e 30 camadas sigma (que acompanham o terreno). Variações sazonais do transporte zonal, estrutura das correntes e distribuição da TSM (Março e Agosto) obtidos numericamente foram avaliados e comparados com dados: de literatura, experimentais do PIRATA e observados por satélite. Os resultados desta simulação mostram que o modelo é capaz de reproduzir os principais aspectos da Subcorrente Equatorial (SE), Contra-corrente Norte Equatorial (CNE), Corrente do Golfo (CG) e os ramos central e norte dos sistemas de Corrente Sul Equatorial (cCSE/nCSE), em diferentes seções ao longo do equador. A comparação entre a estrutura térmica nos primeiros 500 m simulada e do Programa PIRATA mostra uma Camada de Mistura (MLD) bem reproduzida, particularmente, a ressurgência que induz uma MLD mais rasa verificada nas boias mais à leste durante o inverno austral até o final da primavera austral. A evolução sazonal do sistema Piscina Quente do Atlântico Sul (SAWP) Língua Fria (Cold Tongue) foi bem representado, que é importante para futuras previsões de variabilidade climática sobre as fronteiras continentais da parte sudoeste do Atlântico tropical. Do lado sudoeste do Atlântico tropical (05°S-25°S / 20°W-47°W), O ROMS (Regional Ocean Model System) foi utilizado pela primeira vez nesta área para simular a circulação oceânica utilizando uma malha de resolução horizontal de 1/12º com 40 camadas sigma, que acompanham o terreno, para resolução vertical. Para avaliação preliminar da configuração do ROMS adotada foram analisadas as distribuições superficiais e verticais de temperatura, além de calculadas as evoluções sazonais da camada bem misturada e dos balanços, atmosféricos e oceânicos, envolvendo a troca de calor dentro da camada bem misturada. A ordem de grandeza das componentes oceânicas (principalmente a difusão vertical e a advecção horizontal) é da mesma ordem de grandeza dos forçantes atmosféricos e quase sempre opostos entre si, com alguma diferença de fase e transporte dentro das camadas mais superficiais. Resultados de variabilidade interanual foram comparados com os primeiros dois anos de perfis de temperatura observados advindos dos três fundeios do programa PIRATA-SWE (Projeto PIRATA, Extensão Sudoeste). A estrutura térmica simulada nas camadas mais superficiais do oceano está em concordância com os resultados obtidos in situ. Resultados de simulação apontam para uma larga e relativamente fraca CSE, composta por uma sequência de núcleos não bem definidos e próximos a superfície. O transporte que flui para oeste da CSE nos primeiros 400 m de profundidade ao longo da seção que atravessa as boias PIRATA-SWE, calculado para simulação do ROMS entre 2005-2007, apresenta um volume médio transportado de 14,9 Sv, com um máximo observado em JFM (15,7 Sv) e um mínimo durante MJJ (13.8 Sv). Os resultados de simulação indicam que em 2005-2007 o transporte para oeste da CSE foi modulado pela variabilidade da componente zonal do vento. Três seções zonais, posicionadas do continente até a posição da boia PIRATA, confirmam transporte mais intenso da Sub-corrente do Norte do Brasil (SNB), fluindo para norte, e uma diminuição no transporte da Corrente do Brasil (CB),que flui para sul, durante maio de 2006 e maio de 2007, quando a bifurcação do ramo sul da CSE alcança sua posição mais ao sul. Por outro lado, o máximo escoamento da CB foi registrado durante janeiro de 2006, janeiro de 2007 e março de 2007, com um mínimo da SNB fluindo para norte em dezembro de 2005 e outubro/dezembro 2006, correspondendo ao período em que a bifurcação do ramo sul da CSE alcança sua posição mais ao norte (OND). A Elevação da Superfície do Mar (ESM) e a Energia Cinética turbulenta (ECT) superficial calculada a partir das simulações e dos produtos AVISO Rio05 apontam na superfície para os mais altos níveis de energia de meso-escala ao longo do ramo central da CSE e da SNB/CB. Resultados de modelagem ecológica usando o modelo NPZD acoplado com o ROMS confirmam esta região como uma área oligotrófica. Resultados do modelo ecológico são comparados com SeaWifs dataset e a dinâmica e a produção primária são localmente discutidos. Estes resultados preliminares disponibilizam mais informações diante da complexidade da região de divergência da SCE e encoraja-nos a conduzir estudos mais detalhados a respeito da dinâmica e do transporte de massa nessa região utilizando o ROMS. Este trabalho também apresenta a necessidade de continuação, ampliação e extensão vertical para o sistema de observação PIRATA-SWE, especialmente com medidas de salinidade em mais níveis de profundidade, além da instalação de medidores de correntes
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 textCataloged 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.
Boyle, Patrick Ryan. "Cenozoic Variations in the Deep Western Boundary Current as Recorded in the Seismic Stratigraphy of Contourite Drifts, Newfoundland Ridge, Offshore Canada." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/51850.
Full textMaster of Science
Ponsoni, Leandro. "Sistema Corrente do Brasil: uma proposta para utilização de perfis XBT em seu estudo dinâmico." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-30012015-142610/.
Full textThe Brazil Current (BC) and the Intermediate Western Boundary Current (IWBC) between 20°S and 28°S are perhaps two of the less studied subtropical boundary currents of the world ocean. Within this region, the BC develops vigorous meanders and rings. A combination of numerical simulations and observational studies are important tools to unravel these phenomena. Direct current measurements are rare and usually too short to depict the mean, long term circulation patterns. Similarly, quasi-synoptic hydrographic and ADCP data in the region are sparse. On the other hand, XBT data archived by the Brazilian Navy are abundant. Here we investigate how XBT temperature (T) profiles may improve the study region climatology and be used to generate initialization fields for numerical models. A method for constructing synthetic salinity (S) profiles is proposed considering the complex shape of the TS curve of the area, the shape of the in situ temperature profile and surface salinity. More specifically, surface salinity and nondimensionalized in situ temperature profiles are used for reconstructing salinity in the upper 200 m of the water column for locations with local depth greater than 1899 m. The mean nondimensionalized climatological salinity profile is used for the depth interval between 900 and 1300 m. The nondimensionalized profile is then redimensionalized using values estimated by the climatological TS relationship in its extrema. The salinity vertical profile of the remaining portions of the water column by linear fitting S to T each 25 m interval. It is also necessary to vertically extrapolate the temperature profiles from 1800 m (maximum depth reached by the XBT probes) to the ocean bottom. We propose using the nondimensionalized climatological T profile and the values of the temperature sampled at 1800 m as well as the bottom climatological temperature to redimensionalize it and extend the temperature vertical structure to the local depth. Geostrophic calculations using data from recent quasi-synoptic hydrographic surveys in the area are employed to test the methodology. A comparison between the currently proposed method and the geostrophic velocities calculated by other techniques is conducted. This comparison also includes geostrophic velocity estimates considering: constant salinity (S=35), an adaptation of classical techniques based solely on the TS curve shape, and by direct relating specific volume anomaly and temperature. The method proposed in this work is the one which best reproduces the current vertical structure and current volume transport in mean terms among all tested. In particular, the BC volume transport is virtually identical to the values obtained with the in situ fields.
Mielke, Charlotte Laura [Verfasser], and Johanna [Akademischer Betreuer] Baehr. "The North Atlantic Deep Western Boundary Current : seasonal cycle, decadal variability and relation to the Atlantic Meridional Overturning Circulation / Charlotte Laura Mielke. Betreuer: Johanna Baehr." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2015. http://d-nb.info/1068931078/34.
Full textDomingues, 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.
Full textKöhler, Janna [Verfasser], Monika [Akademischer Betreuer] Rhein, and Torsten [Akademischer Betreuer] Kanzow. "Long-term variability of internal waves and diapycnal mixing: The role of the North Atlantic Deep Western Boundary Current / Janna Köhler. Gutachter: Monika Rhein ; Torsten Kanzow. Betreuer: Monika Rhein." Bremen : Staats- und Universitätsbibliothek Bremen, 2013. http://d-nb.info/1072078686/34.
Full textCalado, Leandro. "Dinâmica da interação da atividade de meso-escala da Corrente do Brasil com o fenômeno da ressurgência costeira ao largo de Cabo Frio e Cabo de São Tomé, RJ." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-24092009-140739/.
Full textThe Brazil Current meanders off the Brazilian southeast coast are unique in terms of their thermohaline structure. These eddies, especially off the Cape Frio and S~ao Tom´e region constitute an integrated system with the Brazil Current and the coastal upwelling, characterizing a dynamic system which we propose to nominate as Brazil Current-eddy-upwelling system. We present a methodology of parametric model construction of the oceanographic features (or Feature Models) which compose the inferred system . These models are capable of three-dimensionally building independent the relevant features from synoptic surface and bottom data in order to compose the initial fields for numerical models with the objective of understanding the dynamics of the interaction of Brazil Current-eddy-upwelling system. By means of numerical simulation usingthe initial fields based on the Feature Models, we investigated the process which conducts to the thermohaline asymmetry of the eddies in the Brazil Current as mentioned above. This is due to the baroclinic approximation of the currents to shallower depths. The penetration of the Central Water in the South Atlantic by the bottom Ekman layer does not have a significant effect on the eddy structure. Additional numerical experiments were carried out with the objective of unders tanding which of the geophysical instabilities were involved in the growth of the Brazil Current meanders and eddies. The results analyzed through calculation of energy conversion allowed us to conclude that the Brazil Current-eddie-upwelling system presents mixed instability (barotropic and baroclinic). However, the baroclinic instability is dominant and is mostly associated to the vertical shear of the oceanic currents. The system, however,was sensitive to the action of the northeast wind shear and consequently to the coastal upwelling. Such sensibility was interpreted as the main responsible for the relevance of barotropic instability in the growth process of meanders in the Brazil Current. Lastly, we verified that a quasi-stationary frontal cyclonic meander, in special growth conditions by instability mechanisms, mayhelp in establishing coastal upwelling. The simulated S~ao Tom´e Cape Eddy presented a very low phase velocity and grew towards the open sea, almost perpendicularly to the continental shelf break. Therefore, the growth of the S~ao Tom´e Cape Eddy advects Coastal Water into its center and, therefore, lead to upwelling of South Atlantic Central Water near the coast. We can therefore say that there are in fact interaction mechanisms between the coastal system and the meso-scale activity of the Brazil Current.
Carvalho, Jéssica dos Santos de. "Variabilidade de longo-termo do transporte da Corrente do Brasil ao longo de 30º S - Um estudo numérico." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-24032015-155510/.
Full textLong term variability has been detected in the South Hemisphere large-scale wind pattern, using models, reanalysis and observations. Recent studies have suggested an oceanic response to changes in the atmospheric pattern, such as the Subtropical Front migration, increase in the Agulhas leakage and intensification of the subtropical gyre (SG). Despite the importance of the South Atlantic in the global heat distribution, the variability of its circulation and response to changes in the large-scale wind field remains unclear. The current study aims to investigate, from a numerical simulation using HYCOM (Hybrid Coordinate Ocean Model), the variability of the Brazilian Current (BC) volume transport at its central region (∼30ºS) according to the wind field from Reanalysis I - NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research). The NCEP/NCAR results show an intensification and a poleward shift of the Southern Hemisphere westerly winds, leading changes in the wind curl along the SA, and a southern migration of the zero and maximum curl lines in subtropical latitudes. Even with the intensification of the mean wind curl over the SA, the time series of integrated Sverdrup return flow transport at 30ºS show a decrease between 1960 and 2010. This pattern is in agreement with the reduction trend in the zonal mean curl along the same latitude. The computed BC transport by HYCOM results present a similar trend to the integrated Sverdup transport (approximately 0.1 Sv per decade), with a 0.6 maximum correlation with a 2 year delay. Along the 30ºS, close to the western boundary, a north flow was identified as the return of a recirculation cell, with a 4,25±2,87 Sv mean transport. This flow also presents a reduction trend, which could be related to southern migration of the entire recirculation structure, following the Brazil-Malvinas confluence and Subtropical Front displacement. The residual transport at the western boundary (BC+Recirculation) shows an increase in the south flow that could indicates an increase of the SG, which is in agreement with the intensification and expansion of the Subtropical Ridge observed in the Reanalysis I. However, no significant correlation between the wind field and residual transport variability along the western boundary was found.
Calixto, Pedro Silveira. "Vórtices da Corrente de Contorno Oeste Profunda do Atlântico ao largo da costa leste brasileira." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/21/21135/tde-24022017-173746/.
Full textThe Deep Western Boundary Current (DWBC) is one of the main components of the Atlantic Meridional Overturning Circulation and is therefor determinant in the maintainance of the global climate. This current has its origins in the subpolar region of the North Atlantic and transports the water mass formed at deep levels to the Southern Hemisphere. Its path as well as its variability have been studied in the last twenty years but information about the DWBC in the South Atlantic are still sparse. Recent investigations showed that the DWBC breaks into large anticyclonic eddies at around 8ºS. In this wrok, we gathered an ample observation data set of oceanographic cruises and used them to describe the vortical rings off the Eastern Brazilian coast. We emplyed the classic dynamics method referenced to 4,000 dbar to infer geostrophic velocity patterns from the data set. We indentify vortical structures of typically 162-220 km of diameter and azimuthal velocities higher than 25 cm s-1. A currentmeter mooring deployed by the University of Kiel in the begining of the century was used to investigate regularity and sazonality of the eddy formation and their passing of the 11ºS paralell. We found by inspecting the 5-year time series that there are about 3,7 events/year and a seasonal modulation dictated by the strength of the DWBC. More rings are shed during the April-September season when the DWBC is more intense and transports more. We also analyzed the output of a assimilative global simulation by the Hybrid Ocean Circulation Model (HYCOM) Consortium after validating it with our observational data set. Our results indicate that the anticyclones propagate at a characteristic speed of about 5cm s-1 until interacts with complex seamount topography at 17ºS. The topography is formed by th Abrolhos Ridge (17ºS), the Seamount Hot Sput (18ºS) and the Vitória-Trindade Ridge (20ºS). Moreover, it seems that the vast majority of the vortical features are destroted on the northernmost obstacle - the Abrolhos Ridge. Only a few survive and are destructed south. It seems from the analysis that a recoalesced DWBC existis nearby 20ºS, where it veers east and flows toward the interior of the Atlantic Ocean basin. We should emphasize that despite the DWBC anticyclones original description is more than a decade old, this is the first work to describe the fate of these large rings off the Eastern Brazil Continental Margin.
Godoi, Sueli Susana de. "Dinâmica quase-geostrófica do sistema corrente do Brasil no embaiamento de São Paulo (23,5º - 27º S)." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-10122009-130359/.
Full textThe Brazil Current System is formed by two western boundary currents that flow along the Southeast Brazil continental margin from surface to 1200-1800 m deep. These two currents are the southward-flowing Brazil Current (BC) and the northward-flowing Intermediate Western Boundary Current (IWBC). The investigation of the dynamics of the barociinic vorticity waves superimposed to the BC system is conducted in this work solely from hydrographic data anaiysis and manipulation from two oceanographic meso-scale surveys that were part of the COROAS Project, the Brazilian arm of the Worid Ocean Circulation Experiment. These two cruises sampled the central portion of the São Paulo Bight (23,5°- 27°S) in the summer and winter seasons of 1993. As it was intended to appiy the classical Dynamic Method to the data, a quantitative estimate of the reference levei (RL) is conducted through the comparison of two different and independent methodoiogies. The first uses the previous knowiedge that the BC transports Tropical Water and South Atlantic Central Water (SACW) as well as that the IWBC transports mainly Antarctic Intermediate Water (AAIW). This method, referred here as the Thermodynamic Criterion applies the Shtokman theorems to estimate the interface depth between SACW and AAIW. The second methodology, designated here as the Dynamic Criterion, consists of modeiing absolute baroclinic velocities for all 14 hydrographic transects using the sectional version of the Princeton Ocean Model. The results of the two methods differ oniy in 7 dbar and a RL of 480 dbar is adopted as to represent the average interface isobaric level between BC and IWBC in the following geostrophic calculations. Horizontal distributions of geostrophic stream function are generated using objective mapping. These distributions present unequivocal evidences of cyclonic and anticyclonic structures in both Summer and Winter 1993 cruises. These features are associated to meanders of the BC System. They are depicted in opposing sides of the current core. The cyclone is seen in the BC coastal side as the anticyclone is placed in its oceanic side. The vertical variation of these pattems with a single flow direction inversion confirms that these vortical features are part of a first baroclinic mode wave, which corroborates previous speculations found in the literature. In order to pursue a potential vorticity analysis, a data-derived two-layer quasi-geostrophic model is built assuming an invicid flat-bottomed ocean in the 3-plane. This analysis allowed to conclude that the basic vorticity field associated with both horizontal and vertical shear of the boundary currents are responsible for the baroclinic wave existence. The planetary vorticity gradient is one order of magnitude lower. The frontal variation in baroclinic potential vorticity is 1,7 x i0 s1. The dominance of the stretching vorticity, which accounts for 60% of the gradient variation, leads to classify these oscillatory motions as long meso-scale waves. The potential vorticity conservation principle is invoked on an analysis that consists of superimposing the first layer quasi-gesotrophic potential vorticity and geostrophic stream funtion maps. This analysis revealed that the baroclinic waves are propagating as well as evidences of meander growth, an indication of a possible geophysical instability mechanism, are seen. Given the findings of the previous analyses, linear theory and the perturbation method are used to derive a dispersion relation for the BC System first mode baroclinic waves. The wave frequency is function of the BC velocity as well as the potential vorticity cross-stream gradient.
Passos, Leilane Gonçalves dos. "Padrões de escoamento baroclínico de mesoescala ao largo do Embaiamento de Tubarão e do Banco de Abrolhos." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-19042012-155513/.
Full textThe region adjacent to the Tubarão Embayment and Abrolhos Bank is maybe one of the less investigated of the Brazillian continental margin. Studies about the cirulation in this area are currently restricted to studies carried out during the 80\'s and 90\'s. Recently, studies focusing the mesoscale activity and the seazonal variability of the circulation off the Brazillian eastern coast have reported complex flow patterns and raised attention of the scientific community to the lack of knowledge of the local dynamics. In order to comprehend the flow pattern in the region, having synoptic data for 2004 and 2005 from the Abrolhos Project, this work aims to study the main features identified in the study area through numerical modelling. With this intent, the initial field was built through hydrographic synoptic data objectively interpolated with monthly climatological fields of the World Ocean Atlas 01. For that, the profiles of the synoptic and climatological data were non-dimensionalyzed and re-dimensionalyzed with thermal satellite images and synthetic salinity field. After the initial field was built, a numerical simulation with the Regional Ocean Modeling System - ROMS was carried out, for the winter (2004) and summer (2005) scenarios. In the winter scenario an anticyclone, here named Tubarão Eddy, was identified inside the Tubarão Embayment, while the Vitória Eddy (VE) and the Abrolhos Eddy (AE) were only identified in the summer scenario, being the VE associated with an anticyclone symetric to the Brazil Current axis. The results deny the hypothesis that the anticyclones offshore the Abrolhos Bank present the same dynamical structure as the cyclones present in the Tubarão Embayment. Besides, we state the non-permanent nature of the VE.
Amorim, Fabiola Negreiros de. "A Dinâmica Sazonal da Plataforma Continental Leste Brasileira entre 10ºS e 16ºS." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-19042012-111805/.
Full textThe seasonal circulation of the Eastern Brazilian Shelf (EBS) between 10oS and 16oS is investigated based on original in situ data sets and hydrodynamic modeling. The observational data provided an understanding of the circulation dynamics within specific parts of the the study region and its interaction with the various forcing mechanisms, illustrating the strong influence of the large/meso scales atmospheric and oceanic circulation, transient processes and local topography on the regional circulation, presenting very distinct scenarios between seasons. The hydrodynamic modeling results not only complemented the observational studies but also allowed for a broader understanding of the seasonality and time-space variability of the EBS circulation, as well as its interaction with the various forcing mechanisms, in a wider region (10oS-16oS). The EBS is highly affected by large-scale seasonality in the trade wind regime and the latitude of the Intertropical Convergence Zone (ITCZ). Following this dynamics, during the spring/summer seasons, the currents within the continental shelf south of 12oS are influenced by preferential E-NE winds and, in the ocean, the bifurcation of the South Equatorial Current (bSEC) reaches its northernmost position (~13oS in November). At the shelf break and slope region, the currents are also influenced by the Western Boundary Currents (WBC). At the northern domain (10oS) the inner shelf circulation is to the south following the preferential winds, while the circulation at the mid shelf and shelf break is more influence by the currents at the slope, which are clearly dominated by the North Brazil Current/North Brazil Undercurrent (NBC/NBUC) dynamics. At the central region (14oS), although the circulation is somehow similar to that observed for the northern domain, the slope circulation presents a greater variability in response to the presence of the opposing Brazil Current (BC) and NBUC flow. At the southern domain (16oS) the circulation has a clear division along the continental shelf/slope regions, presenting an intense and organized southward flow at the inner and mid shelves, as a response to the remote wind forcing, and a polarized cross-shelf circulation at the shelf break/slope region, suggesting an association with the WBC and the local topography of the Royal Charlotte Bank. During the autumn/winter seasons, following the seasonal regime of the trade winds and the latitude of the ITCZ, the continental shelf north of ~20oS are influenced by preferential E-SE winds and the currents experience a reversal of the mean flow, and the bSEC reaches its southernmost position (~17oS in July). The circulation during these seasons at the northern domain inner and mid shelves presents a weak northward flow with a strong variability. While at the inner shelf this variability is related to the more frequent cold front passages at the mid shelf it is related to the slope region circulation. The circulation at this region has a high correlation with the circulation at the shelf break and both present a less variable and more intense northward net flow which could be related to the NBC/NBUC flow, that occupies the entire slope region during these seasons. The northward net flow at the central domain presents a weak intensity and high variability at the inner/mid shelves and shelf break regions, which could be related to the increase in the cold fronts frequency, to the fact that this region is under the influence of the bifurcation of the surface net flow and, for the shelf break region, to the NBUC variability which presents more episodes that occupies this region. At the slope region the NBC/NBUC exerts a clear influence in the circulation. The circulation at the southern domain is mainly driven by the remote wind forcing at the inner and mid shelves, while at the shelf break/slope regions presents a significant WBC influence.
Yamashita, Cintia. "Foraminíferos bentônicos vivos na margem sudoeste do Atlântico Sul, Bacia de Campos: processos oceanográficos condicionantes." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/21/21136/tde-23032016-110128/.
Full textThe present study comprises the analysis of the distribution of living benthic foraminifera on the continental slope of Campos Basin and Plateau of São Paulo (400-3000 m water depth) in order to understand the environmental processes determining this distribution. Sedimentological, geochemical and microfaunal data indicated the existence of three groups in the study area. Group I includes samples from the upper and middle slope (400-1300 m water depth) and is characterized by high values of benthic foraminifera density, total organic carbon, phytopigment concentration, biomass of bacteria, lower values of sortable silt and calcium carbonate content, and the presence of species such as Globocassidulina subglobosa, Reophax scorpiurus, Reophax subfusiformis, Reophax spiculotestus and Epistominella exigua. Group II, consisting of samples of the lower slope and Plateau of São Paulo (1900-3000 m water depth), is characterized by lower densities of benthic foraminifera, total organic carbon, phytopigment concentration, biomass of bacteria, higher values of sortable silt and calcium carbonate content, and the presence of species such as Saccorhiza ramosa, Rhizammina algaeformis, Karrerulina sp2. and Hyperammina rugosa. Group III (1900-3000 m water depth) differs from group II due to the presence of Glomospira gordialis, Pyrgoella irregularis and Reophax helenae. Hydro-sedimentary processes (e.g. action of the Brazil Current and Intermediate Western Boundary Current), the particulate organic matter flux and phytopigment concentration in the sediment are factors controlling the trophic conditions in the environment, and are related to features of mesoscale (meanders and Cabo Frio, Cabo de São Tomé and Vitória eddies), thereby determining changes in living benthic foraminifera in Campos Basin.
Steinmoeller, Derek. "Flow Separation on the β-plane." Thesis, 2009. http://hdl.handle.net/10012/4417.
Full textChang, Kuang-Yu, and 張光宇. "Western Boundary Current Intensification Modeling with Chebyshev and Immerse Boundary Methods." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/45206726069399275065.
Full text國立臺灣大學
大氣科學研究所
98
ABSTRACT By simulating the famouse Western Boundary Current (WBC), this thesis first integrate Chebyshev collocation method with Ghost Cell Immersed BoundaryMethod (GCIBM) into a powerful coupled model. WBC intensification is caused by wave energy accumulation at the western boundary of the ocean basins, causing a narrow region which has higher meridional velocity than anywhere else. Complex boundary geometry may also strongly affect the WBC which is difficult to handle in the numerical model. In order to solve this problem and increase flexibility, we use GCIBM to implicitly provide the boundary conditions for the numerical model. GCIBM is an advanced numerical method, based on the use of artificial forcing to represent the effect of the realistic boundaries on the flow. To accurately resolve the wave dynamic, we employee the Chebyshev Collocation method with exponential solution convergence rate. Combing GCIBM with Chebyshev Collocation method, we present high accuracy and flexibility barotropic model of different complexity to simulate the WBC intensification in the β plane ocean. The numerical results show that both Chebyshev Collocation method and central difference with GCIBM can provide a reasonable WBC. The width of the WBC agrees well with the theoretical one. It seems that during the transient state Rossby waves play an important role in the generation of WBC, causing the asymmetric property in the nearly symmetric ocean, while the nonlinear dynamics would redistribute the wave energy of the ocean. Besides single domain modeling, we use domain decomposition to integrate Chebyshev collocation method with GCIBM. The resluts sugesst that the arrangments of grids at the embedding regions are essential to the coupled model; Chebyshev collocation method and GCIBM would work efficeintly through domain decomposition with the embedding grids matching exactly between the subdomains. However, as long as the embedding grids don’t match each other; interpolation schemes are used in the two-way embedding algorithms, which would cause the mass flux inconsistency between the subdomains due to the difference grid resolutions. This numerical inconsistency would lead to error accumulation at the embedding regions, restricting the effective prediction time steps in the coupled models. Our research suggest that size ratio between GCIBM and Chebyshev collocation method subdomains should be larger than onesixth for the couplde model to run effectively; furthermore, we notice that both mass flux tuning and solution cnovergence rate matching between the subdomains could enlonggate the effective prediction time steps in the coupled models.
Kao, YingHsun, and 高英勛. "The Influence of the ridge across the Western boundary current." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/66742591730618496268.
Full text國立臺灣大學
海洋研究所
86
Analysising the bouy data of WOCE/KSVP, the RyuKyu arc showsits effect to the path of Kuroshio. A branch of Kuroshio turns toeastward and moves as wav es. Developing a barotropic numerical model to examine the influence of the r idge across the Western boundary current. According to model results, the rid ge leads toTaylor column effect, blocks the northward flow and forces it totur n to eastward. Analysising the balance of vorticity, in the southern region o f the ridge, some non-linear performance likerecirculation or Rossby wave can be found, and it has almost thesame dynamic structure of the Northwestern regi on of the generalwind-driven ocean circulation. The length of the ridge, its location and the width of the channel between boundary and ridgedetermine the pattern of this region.
Kim, Younggy. "Ionic separation in electrodialysis : analyses of boundary layer, cationic partitioning, and overlimiting current." Thesis, 2010. http://hdl.handle.net/2152/ETD-UT-2010-08-1724.
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Stöber, Uwe [Verfasser]. "Mixing and energy flux estimates from hydrographic measurements in the deep western boundary current of the North Atlantic / von Uwe Stöber." 2009. http://d-nb.info/994837429/34.
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