Academic literature on the topic 'Western boundary current instability'
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Journal articles on the topic "Western boundary current instability"
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Hristova, Hristina G., Joseph Pedlosky, and Michael A. Spall. "Radiating Instability of a Meridional Boundary Current." Journal of Physical Oceanography 38, no. 10 (October 1, 2008): 2294–307. http://dx.doi.org/10.1175/2008jpo3853.1.
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Abstract A linear stability analysis of a meridional boundary current on the beta plane is presented. The boundary current is idealized as a constant-speed meridional jet adjacent to a semi-infinite motionless far field. The far-field region can be situated either on the eastern or the western side of the jet, representing a western or an eastern boundary current, respectively. It is found that when unstable, the meridional boundary current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field. This is the so-called radiating instability and is found in both barotropic and two-layer baroclinic configurations. A second but important conclusion concerns the differences in the stability properties of eastern and western boundary currents. An eastern boundary current supports a greater number of radiating modes over a wider range of meridional wavenumbers. It generates waves with amplitude envelopes that decay slowly with distance from the current. The radiating waves tend to have an asymmetrical horizontal structure—they are much longer in the zonal direction than in the meridional, a consequence of which is that unstable eastern boundary currents, unlike western boundary currents, have the potential to act as a source of zonal jets for the interior of the ocean.
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Goldsworth, Fraser W., David P. Marshall, and Helen L. Johnson. "Symmetric Instability in Cross-Equatorial Western Boundary Currents." Journal of Physical Oceanography 51, no. 6 (June 2021): 2049–67. http://dx.doi.org/10.1175/jpo-d-20-0273.1.
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AbstractThe upper limb of the Atlantic meridional overturning circulation draws waters with negative potential vorticity from the Southern Hemisphere into the Northern Hemisphere. The North Brazil Current is one of the cross-equatorial pathways in which this occurs: upon crossing the equator, fluid parcels must modify their potential vorticity to render them stable to symmetric instability and to merge smoothly with the ocean interior. In this work a linear stability analysis is performed on an idealized western boundary current, dynamically similar to the North Brazil Current, to identify features that are indicative of symmetric instability. Simple two-dimensional numerical models are used to verify the results of the stability analysis. The two-dimensional models and linear stability theory show that symmetric instability in meridional flows does not change when the nontraditional component of the Coriolis force is included, unlike in zonal flows. Idealized three-dimensional numerical models show anticyclonic barotropic eddies being spun off as the western boundary current crosses the equator. These eddies become symmetrically unstable a few degrees north of the equator, and their PV is set to zero through the action of the instability. The instability is found to have a clear fingerprint in the spatial Fourier transform of the vertical kinetic energy. An analysis of the water mass formation rates suggest that symmetric instability has a minimal effect on water mass transformation in the model calculations; however, this may be the result of unresolved dynamics, such as secondary Kelvin–Helmholtz instabilities, which are important in diabatic transformation.
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Qiu, Bo, Shuiming Chen, Daniel L. Rudnick, and Yuji Kashino. "A New Paradigm for the North Pacific Subthermocline Low-Latitude Western Boundary Current System." Journal of Physical Oceanography 45, no. 9 (September 2015): 2407–23. http://dx.doi.org/10.1175/jpo-d-15-0035.1.
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AbstractSubthermocline western boundary circulation along the low-latitude North Pacific Ocean (2°–25°N) is investigated by using profiling float and historical CTD/expendable CTD (XCTD) data and by analyzing an eddy-resolving global OGCM output. In contrast to the existing paradigm depicting it as a reversed pattern of the wind-driven circulation above the ventilated thermocline (i.e., depth < 26.8 σθ), the subthermocline western boundary circulation is found to comprise two components governed by distinct dynamical processes. For meridional scales shorter than 400 km, the boundary flows along the Philippine coast exhibit convergent patterns near 7°, 10°, 13°, and 18°N, respectively. These short-scale boundary flows are driven by the subthermocline eastward zonal jets that exist coherently across the interior North Pacific basin and are generated by the triad instability of wind-forced annual baroclinic Rossby waves. For meridional scales longer than 400 km, a time-mean Mindanao Undercurrent (MUC) is observed from 6° to 13°N together with another northward-flowing boundary flow beneath the Kuroshio from 16° to 24°N. Rather than remote eddy forcing from the interior Pacific Ocean, both of these broad-scale subthermocline boundary flows are induced by baroclinic instability of the overlying wind-driven western boundary currents, the Mindanao Current, and Kuroshio.
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Fantini, Maurizio, and Ka-Kit Tung. "On Radiating Waves Generated from Barotropic Shear Instability of a Western Boundary Current." Journal of Physical Oceanography 17, no. 8 (August 1987): 1304–8. http://dx.doi.org/10.1175/1520-0485(1987)017<1304:orwgfb>2.0.co;2.
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Waterman, Stephanie, and Brian J. Hoskins. "Eddy Shape, Orientation, Propagation, and Mean Flow Feedback in Western Boundary Current Jets." Journal of Physical Oceanography 43, no. 8 (August 1, 2013): 1666–90. http://dx.doi.org/10.1175/jpo-d-12-0152.1.
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Abstract This manuscript revisits a study of eddy–mean flow interactions in an idealized model of a western boundary current extension jet using properties of the horizontal velocity correlation tensor to diagnose characteristics of average eddy shape, orientation, propagation, and mean flow feedback. These eddy characteristics are then used to provide a new description of the eddy–mean flow interactions observed in terms of different ingredients of the eddy motion. The diagnostics show patterns in average eddy shape, orientation, and propagation that are consistent with the signatures of jet instability in the upstream region and wave radiation in the downstream region. Together they give a feedback onto the mean flow that gives the downstream character of the jet and drives the jet's recirculation gyres. A breakdown of the eddy forcing into contributions from individual terms confirms the expected role of cross-jet gradients in meridional eddy tilt in stabilizing the jet to its barotropic instability; however, it also reveals important roles played by the along-jet evolution of eddy zonal–meridional elongation. It is the mean flow forcing derived from these patterns that acts to strengthen and extend the jet downstream and forces the time-mean recirculation gyres. This understanding of the dependence of mean flow forcing on eddy structural properties suggests that failure to adequately resolve eddy elongation could underlie the weakened jet strength, extent, and changed recirculation structure seen in this idealized model for reduced spatial resolutions. Further, it may suggest new ideas for the parameterization of this forcing.
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Nishigaki, Hajime, and Humio Mitsudera. "Subtropical Western Boundary Currents over Slopes Detaching from Coasts with Inshore Pool Regions: An Indication to the Kuroshio Nearshore Path." Journal of Physical Oceanography 42, no. 2 (February 1, 2012): 306–20. http://dx.doi.org/10.1175/jpo-d-11-076.1.
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Abstract The dynamics of subtropical western boundary currents over slopes detaching from coasts with inshore pool regions, where the water of the subtropical gyre does not enter and the velocity is small, are investigated. This study is intended to understand the dynamics of the nearshore path of the Kuroshio, which has a distinct boundary between the boundary current and the coastal water. Numerical experiments under idealized conditions are made. The results show flow patterns with pool regions similar to the Kuroshio under simple conditions. A deep countercurrent is present on the lower bottom slope, which represents observed deep currents. This is part of a deep cyclonic recirculation north of the jet, which extends to the lower bottom slope despite steep topography. This extension can be explained by the geostrophic contours. In this region, the upper boundary current feels the bottom slope and the westward intensification is blocked. In the other region, where the bottom-layer velocity is very small, the upper boundary current is free from the bottom slope and westward intensification occurs at the coast. The sensitivity to the volume transport of the boundary current is investigated by case studies. The pool regions are broken in cases with large volume transports. It is indicated that these unsteady inshore regions are produced by instability caused by an outcrop of the upper isopycnal, which is led by a large baroclinic volume transport.
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Todd, Robert E., W. Brechner Owens, and Daniel L. Rudnick. "Potential Vorticity Structure in the North Atlantic Western Boundary Current from Underwater Glider Observations." Journal of Physical Oceanography 46, no. 1 (January 2016): 327–48. http://dx.doi.org/10.1175/jpo-d-15-0112.1.
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AbstractPotential vorticity structure in two segments of the North Atlantic’s western boundary current is examined using concurrent, high-resolution measurements of hydrography and velocity from gliders. Spray gliders occupied 40 transects across the Loop Current in the Gulf of Mexico and 11 transects across the Gulf Stream downstream of Cape Hatteras. Cross-stream distributions of the Ertel potential vorticity and its components are calculated for each transect under the assumptions that all flow is in the direction of measured vertically averaged currents and that the flow is geostrophic. Mean cross-stream distributions of hydrographic properties, potential vorticity, and alongstream velocity are calculated for both the Loop Current and the detached Gulf Stream in both depth and density coordinates. Differences between these mean transects highlight the downstream changes in western boundary current structure. As the current increases its transport downstream, upper-layer potential vorticity is generally reduced because of the combined effects of increased anticyclonic relative vorticity, reduced stratification, and increased cross-stream density gradients. The only exception is within the 20-km-wide cyclonic flank of the Gulf Stream, where intense cyclonic relative vorticity results in more positive potential vorticity than in the Loop Current. Cross-stream gradients of mean potential vorticity satisfy necessary conditions for both barotropic and baroclinic instability within the western boundary current. Instances of very low or negative potential vorticity, which predispose the flow to various overturning instabilities, are observed in individual transects across both the Loop Current and the Gulf Stream.
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Napolitano, Dante C., Ilson C. A. da Silveira, Cesar B. Rocha, Glenn R. Flierl, Paulo H. R. Calil, and Renato P. Martins. "On the Steadiness and Instability of the Intermediate Western Boundary Current between 24° and 18°S." Journal of Physical Oceanography 49, no. 12 (December 2019): 3127–43. http://dx.doi.org/10.1175/jpo-d-19-0011.1.
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AbstractThe Intermediate Western Boundary Current (IWBC) transports Antarctic Intermediate Water across the Vitória–Trindade Ridge (VTR), a seamount chain at ~20°S off Brazil. Recent studies suggest that the IWBC develops a strong cyclonic recirculation in Tubarão Bight, upstream of the VTR, with weak time dependency. We herein use new quasi-synoptic observations, data from the Argo array, and a regional numerical model to describe the structure and variability of the IWBC and to investigate its dynamics. Both shipboard acoustic Doppler current profiler (ADCP) data and trajectories of Argo floats confirm the existence of the IWBC recirculation, which is also captured by our Regional Oceanic Modeling System (ROMS) simulation. An “intermediate-layer” quasigeostrophic (QG) model indicates that the ROMS time-mean flow is a good proxy for the IWBC steady state, as revealed by largely parallel isolines of streamfunction and potential vorticity ; a scatter diagram also shows that the IWBC is potentially unstable. Further analysis of the ROMS simulation reveals that remotely generated, westward-propagating nonlinear eddies are the main source of variability in the region. These eddies enter the domain through the Tubarão Bight eastern edge and strongly interact with the IWBC. As they are advected downstream and negotiate the local topography, the eddies grow explosively through horizontal shear production.
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GRIFFITHS, ROSS W., and ANDREW E. KISS. "Flow regimes in a wide ‘sliced-cylinder’ model of homogeneous beta-plane circulation." Journal of Fluid Mechanics 399 (November 25, 1999): 205–36. http://dx.doi.org/10.1017/s0022112099006370.
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We report new experiments with the ‘sliced-cylinder’ β-plane model of Pedlosky & Greenspan (1967) and Beardsley (1969), but with a much wider basin such that the western boundary current and its eddies occupy a small fraction of the basin width. These experiments provide new insights into nonlinear aspects of the flow: the critical conditions for boundary current separation and the transition from stable to unstable flow are redefined, and a further transition from periodic to chaotic eddy shedding under strong anticyclonic forcing is also found. In the nonlinear regimes the western boundary current separates from the western wall and shoots into the interior as a narrow jet that undergoes a rapid adjustment to join with the broad slow interior flow. In the unstable regimes this adjustment involves eddy shedding. Each transition occurs at a fixed critical value of a Reynolds number Reγ based on the velocity and width scales for a purely viscous boundary current: the flow is unstable for Reγ > 123±4 and aperiodic for Reγ > 231±5. The results provide evidence that the mechanism causing instability is shear in the separated jet rather than the breaking of a large-amplitude Rossby wave. A quasi-geostrophic numerical model applied to the laboratory conditions yields a stability boundary and detailed characteristics of the flow largely consistent with those determined from the experiments. It also reveals a strong dependence of the circulation pattern on basin aspect ratio, and shows that an adverse higher-order pressure gradient is responsible for western boundary current separation in this model. Eddy–eddy interactions and feedback of fluctuations from the eddy formation region to upstream parts of the boundary current contribute to aperiodic behaviour. As a result of eddy shedding, passive tracer from each streamline in the boundary current can be stirred across much of the width of the basin.
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Spall, Michael A., Robert S. Pickart, Paula S. Fratantoni, and Albert J. Plueddemann. "Western Arctic Shelfbreak Eddies: Formation and Transport." Journal of Physical Oceanography 38, no. 8 (August 1, 2008): 1644–68. http://dx.doi.org/10.1175/2007jpo3829.1.
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Abstract The mean structure and time-dependent behavior of the shelfbreak jet along the southern Beaufort Sea, and its ability to transport properties into the basin interior via eddies are explored using high-resolution mooring data and an idealized numerical model. The analysis focuses on springtime, when weakly stratified winter-transformed Pacific water is being advected out of the Chukchi Sea. When winds are weak, the observed jet is bottom trapped with a low potential vorticity core and has maximum mean velocities of O(25 cm s−1) and an eastward transport of 0.42 Sv (1 Sv ≡ 106 m3 s−1). Despite the absence of winds, the current is highly time dependent, with relative vorticity and twisting vorticity often important components of the Ertel potential vorticity. An idealized primitive equation model forced by dense, weakly stratified waters flowing off a shelf produces a mean middepth boundary current similar in structure to that observed at the mooring site. The model boundary current is also highly variable, and produces numerous strong, small anticyclonic eddies that transport the shelf water into the basin interior. Analysis of the energy conversion terms in both the mooring data and the numerical model indicates that the eddies are formed via baroclinic instability of the boundary current. The structure of the eddies in the basin interior compares well with observations from drifting ice platforms. The results suggest that eddies shed from the shelfbreak jet contribute significantly to the offshore flux of heat, salt, and other properties, and are likely important for the ventilation of the halocline in the western Arctic Ocean. Interaction with an anticyclonic basin-scale circulation, meant to represent the Beaufort gyre, enhances the offshore transport of shelf water and results in a loss of mass transport from the shelfbreak jet.
Dissertations / Theses on the topic "Western boundary current instability"
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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/.
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This dissertation examines the nature of jet-boundary interactions and the role of barotropic instabilities in the Brazil Current system while still attached to the western boundary. The motivation was due to the frequent observation of bipolar features associated to the Brazil Current flow south of Cape Frio (RJ) and off Santos Bight (22º-28ºS). Such observations were mainly obtained from sea surface temperature images, and also from few \"in situ\" hydrographic and direct velocity measurements data. Therefore, our main focus is on the formation of bipolar features associated with the flow, and the main hypothesis is that barotropic instability is responsible for the generation of such dipoles along the western boundary current jet, while it has to deal with topographic variations along its path poleward. We address the system dynamics from a semi-theoretical perspective, and also through the application of numerical modeling on a process study approach. So it includes semi-theoretical studies of jet-lateral boundary interactions in idealized configurations relevant to the Brazil Current system off Cape Frio, considering the quasi-geostrophic theory as an appropriate approximation of the system we want to investigate. Additionally, numerical modeling is used through the construction of idealized scenarios where we simplify the physics in order to isolate the dynamical process of interest. All the dynamical analyzes were initialized from synoptic hydrographic data set which comprised the Brazil Current system off Cape Frio region. We validated the quasi-geostrophic theory we assumed and obtained the kinematics characteristics of the jet. In the dynamical analyses, we started the investigation from the simplest framework applied here, where we evaluate a piecewise constant potential vorticity field in a quasi-geostrophic contour dynamics model. It dealt with a meridionally-oriented jet flowing southward along a straight western boundary. Next, in a second model, we added more complexity in the system, idealizing western boundary coastline scenarios considering a quasi-continuous potential vorticity field in a quasi-geostrophic numerical model. Finally, in a third model, we constructed a more complex scenario for the Brazil Current jet that incorporated real topography and stratification of the water column in a primitive equation numerical model. Among our main finds, we verified that purely barotropic instability is able to generate vortex dipoles. Moreover, variations in the western boundary can indeed trigger perturbations in the jet and dipoles form. Therefore, sites with abrupt change in bathymetry and coastline orientation are preferred to the formation of the BC vortical dipoles. Vortex streets and instability trains can also develop downstream of such locations as consequence of perturbing a potentially batropically unstable jet. Hence, the horizontal shear is key to the generation of vortex dipoles. A weak shear does not allow these features to form, instead, frontal eddies are possibly generated, with the predominance of anticyclones. Although the three different model strategies applied here differ in dynamical configurations and approximations, they still kept nearly the same regime for the Brazil Current vortex-dipole formation. Topographic variations such as those associated with the change of coastline orientation near Cape Frio (23ºS) account for those vortex dipoles and streets be dominantly observed within the Santos Bight.A 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.
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Soares, Saulo Muller. "Ondas instáveis no sistema de correntes de contorno oeste ao largo de Abrolhos." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-19072007-145643/.
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O sistema de correntes de contorno oeste que flui ao largo da costa leste brasileira entre 15°S e 22°S, é composto pela Corrente do Brasil (CB) fluindo para sul, a Sub-Corrente Norte do Brasil (SNB) fluindo para norte e a Corrente de Contorno Oeste Profunda (CCP) também fluindo para sul. Vigorosos meandros e vórtices são observados à jusante dos Bancos de Abrolhos (BA) e Royal Charlotte (BRC) e da Cadeia Vitória-Trindade. O objetivo central desta dissertação é o estudo da estabilidade deste sistema de correntes, aqui denomidado Sistema CB-SNB-CCP, utilizando o modelo oceânico da Universidade de Princeton (POM) em um cenário idealizado. Buscamos responder o quão instável é este sistema e quais seriam as características das ondas instáveis geradas a fim de contribuir para o conhecimento acerca da rica dinâmica de meso-escala observada nesta região. Objetivamos também, elucidar o papel dos BA e BRC nesta dinâmica. Embasados na alta baroclinicidade do sistema de correntes de contorno ao largo do sudeste brasileiro, optamos por representar o escoamento CB-SNB-CCP através de um modelo paramétrico do campo de massa, calibrado com os dados hidrográficos oriundos dos Cruzeiros Abrolhos [Silveira et al., 2006]. Mantendo o caráter idealizado do estudo, também empregamos topografia de fundo analítica, onde representamos o talude da região por uma função tangente hiporbólica. O BA e o BRC foram aproximados através de funções gaussianas devidademente ajustadas aos contornos da isóbata de 80 m extraídas do conjunto ETOPO 2. Para identificar os mecanismos de crescimento das possíveis ondas instáveis, calculou-se o balanço de energia das simulações realizadas de acordo com o método de [Xue & Bane, 1997]. Os resultados de três experimentos numéricos realizados sugerem que o sistema CB-SNB-CCP é instável. Ciclones quase-estacionários do lado costeiro da CB surgem como o principal modo de variabilidade desta corrente. De acordo com a análise do balanço energético, o crescimento dessas feições resulta primariamente de instabilidade baroclínica do escoamento. A escala horizontal típica das ondas e vórtices instáveis modelados é dada pelo raio de deformação interno, como esperado pela teoria de instabilidade baroclínica de escoamentos realisticamente estratificados. Em particular, os resultados do experimento com o BA e o BRC idealizados comprovam que estes funcionam como gatilhos para o desenvolvimento de ondas instáveis, favorecendo amplamente o crescimento das estruturas verticais. Os trens de onda instáveis quase-estacionários aqui obtidos sugerem que provavelmente o meandramento da CB observado em latitudes que se estendem até 28°S pode ser parte de um único sistema que se origina na região dos BA e BRC.The western boundary currents system that flows off the eastern brazilian coast between 15°S e 22°S is composed by the southward-flowing Brazil Current (BC), the northward-flowing North Brazil Under Current (NBUC) and the Deep Western Boundary Current (DWBC) that flows south. Vigorous meanders and eddies are observed downstream of the Abrolhos (AB) and Royal Charlotte Banks (RCB) and the Vitória-Trindade Ridge. The main goal of this dissertation is to study the stability of this currents system, hereby named BC-NBUC-DWBC system, using the Princeton University Ocean Model (POM) in an idealized scenerio. We seek to answer how unstable is this system and what are the characteristics of the unstable waves in order to contribute to the understanding of the rich mesoescale dynamics observed in this region. We also aim to elucidate the role of the AB and of the RCB on this dynamics. Based on the high degree of baroclinicity of the western boundary currents system off the southeastern brazilian coast, we opted to represent the BC-NBUC-DWBC system through a parametric model of the mass field, calibrated with hydrographic data from the Abrolhos Cruises [Silveira et al., 2006]. Maintaining the idealized character of the study, we have also employed an analytical bottom topography, in which the region\'s continental slope is approximated by hyperbolic tangent function. The AB and RCB were approximated by gaussian functions properly adjusted to the 80 m isobath extracted from the ETOPO 2 database. To identify the growth mecanism of the unstable waves, the energy budget of the simulations was calculated according to [Xue & Bane, 1997]. The results from the three experiments conducted here suggest that the BC-NBUC-DWBC system is indeed unstable. Quasi-stationary cyclones in the coastal side of BC arise as the main mode of variability of this current. According to the energy budget analisys, the growth of these features results primarily from baroclinic instability of BC-NBUC-DWBC flow. The typical horizontal scale of the modeled unstable waves and eddies is given by the internal radius of deformation, as expected by baroclinic instability theory of realistically stratified flows. The quasi-stationary unstable wave trains modeled in the present study also suggest that the meandering of the BC observed down to 28°S are probably part of a single system that originates at the AB and RCB region.
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Kiss, 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.
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This thesis presents a numerical exploration of the dynamics governing
rotating flow driven by a surface stress in the " sliced cylinder " model
of Pedlosky & Greenspan (1967) and Beardsley (1969), and its close
relative, the " sliced cone " model introduced by Griffiths & Veronis
(1997). The sliced cylinder model simulates the barotropic wind-driven
circulation in a circular basin with vertical sidewalls, using a depth
gradient to mimic the effects of a gradient in Coriolis parameter. In the
sliced cone the vertical sidewalls are replaced by an azimuthally uniform
slope around the perimeter of the basin to simulate a continental slope.
Since these models can be implemented in the laboratory, their dynamics
can be explored by a complementary interplay of analysis and numerical
and laboratory experiments. ¶
In this thesis a derivation is presented of a generalised
quasigeostrophic formulation which is valid for linear and moderately
nonlinear barotropic flows over large-amplitude topography on an f-plane,
yet retains the simplicity and conservation properties of the standard
quasigeostrophic vorticity equation (which is valid only for small depth
variations). This formulation is implemented in a numerical model based
on a code developed by Page (1982) and Becker & Page (1990). ¶
The accuracy of the formulation and its implementation are confirmed by
detailed comparisons with the laboratory sliced cylinder and sliced cone
results of Griffiths (Griffiths & Kiss, 1999) and Griffiths & Veronis
(1997), respectively. The numerical model is then used to provide insight
into the dynamics responsible for the observed laboratory flows. In the
linear limit the numerical model reveals shortcomings in the sliced cone
analysis by Griffiths & Veronis (1998) in the region where the slope and
interior join, and shows that the potential vorticity is dissipated in an
extended region at the bottom of the slope rather than a localised region
at the east as suggested by Griffiths & Veronis (1997, 1998). Welander's
thermal analogy (Welander, 1968) is used to explain the linear
circulation pattern, and demonstrates that the broadly distributed
potential vorticity dissipation is due to the closure of geostrophic
contours in this geometry. ¶
The numerical results also provide insight into features of the flow at
finite Rossby number. It is demonstrated that separation of the western
boundary current in the sliced cylinder is closely associated with a
" crisis " due to excessive potential vorticity dissipation in the viscous
sublayer, rather than insufficient dissipation in the outer western
boundary current as suggested by Holland & Lin (1975) and Pedlosky
(1987). The stability boundaries in both models are refined using the
numerical results, clarifying in particular the way in which the western
boundary current instability in the sliced cone disappears at large
Rossby and/or Ekman number. A flow regime is also revealed in the sliced
cylinder in which the boundary current separates without reversed flow,
consistent with the potential vorticity " crisis " mechanism. In addition
the location of the stability boundary is determined as a function of the
aspect ratio of the sliced cylinder, which demonstrates that the flow is
stabilised in narrow basins such as those used by Beardsley (1969, 1972,
1973) and Becker & Page (1990) relative to the much wider basin used by
Griffiths & Kiss (1999). ¶
Laboratory studies of the sliced cone by Griffiths & Veronis (1997)
showed that the flow became unstable only under anticyclonic forcing. It
is shown in this thesis that the contrast between flow under cyclonic and
anticyclonic forcing is due to the combined effects of the relative
vorticity and topography in determining the shape of the potential
vorticity contours. The vorticity at the bottom of the sidewall smooths
out the potential vorticity contours under cyclonic forcing, but distorts
them into highly contorted shapes under anticyclonic forcing. In
addition, the flow is dominated by inertial boundary layers under
cyclonic forcing and by standing Rossby waves under anticyclonic forcing
due to the differing flow direction relative to the direction of Rossby
wave phase propagation. The changes to the potential vorticity structure
under strong cyclonic forcing reduce the potential vorticity changes
experienced by fluid columns, and the flow approaches a steady free
inertial circulation. In contrast, the complexity of the flow structure
under anticyclonic forcing results in strong potential vorticity changes
and also leads to barotropic instability under strong forcing. ¶
The numerical results indicate that the instabilities in both models
arise through supercritical Hopf bifurcations. The two types of
instability observed by Griffiths & Veronis (1997) in the sliced cone are
shown to be related to the western boundary current instability and
" interior instability " identified by Meacham & Berloff (1997). The
western boundary current instability is trapped at the western side of
the interior because its northward phase speed exceeds that of the
fastest interior Rossby wave with the same meridional wavenumber, as
discussed by Ierley & Young (1991). ¶
Numerical experiments with different lateral boundary conditions are also
undertaken. These show that the flow in the sliced cylinder is
dramatically altered when the free-slip boundary condition is used
instead of the no-slip condition, as expected from the work of Blandford
(1971). There is no separated jet, because the flow cannot experience a
potential vorticity " crisis " with this boundary condition, so the western
boundary current overshoots and enters the interior from the east. In
contrast, the flow in the sliced cone is identical whether no-slip,
free-slip or super-slip boundary conditions are applied to the horizontal
flow at the top of the sloping sidewall, except in the immediate vicinity
of this region. This insensitivity results from the extremely strong
topographic steering near the edge of the basin due to the vanishing
depth, which demands a balance between wind forcing and Ekman pumping on
the upper slope, regardless of the lateral boundary condition. The
sensitivity to the lateral boundary condition is related to the
importance of lateral friction in the global vorticity balance. The
integrated vorticity must vanish under the no-slip condition, so in the
sliced cylinder the overall vorticity budget is dominated by lateral
viscosity and Ekman friction is negligible. Under the free-slip condition
the Ekman friction assumes a dominant role in the dissipation, leading to
a dramatic change in the flow structure. In contrast, the much larger
depth variation in the sliced cone leads to a global vorticity balance in
which Ekman friction is always dominant, regardless of the boundary
condition.
4
Waterman, 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 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), 2009.Includes 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.
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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 textAbstract:
Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences and the Woods Hole Oceanographic Institution), February 2001.Includes bibliographical references (p. 116-118).
6
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 textAbstract:
Thesis (S.M.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 2001.Includes bibliographical references (p. 116-118).
I study the exchange between a boundary current and flanking horizontal recirculations in a 'sliced-cylinder' rotating tank laboratory experiment. Two flow configurations are investigated: a single recirculation and a double, figure-8, recirculation. The latter case involves a hyperbolic point, while the former does not. I investigate the stirring and mixing under both steady and unsteady forcing. I quantify the mixing in each case using effective diffusivity, Keff, and a corollary effective length, Leff, as derived by Nakamura (1995, 1996). This approach involves diagnosing the geometric complexity of a tracer field. Geometric complexity is indicative of advective stirring. Because stirring creates high gradients, flows with high advective stirring also have high diffusion, and stronger overall mixing. I calculate effective length from images of dye in the tank and find much higher values of Leff in the unsteady hyperbolic cases than in the other cases. Slight unsteadiness in flows involving hyperbolic points gives rise to a chaotic advection mechanism known as 'lobe dynamics'. These lobes carry fluid in and out of the recirculations, acting as extremely effective stirring mechanisms. I demonstrate the existence of these exchange lobes in the unsteady hyperbolic (figure-8) flow. The velocity field in the tank is calculated utilizing particle image velocimetry (PIV) techniques and a time series U(t) demonstrates the (forced) unsteadiness in the flow. Images of dye in the tank show exchange lobes forming at this same forcing period, and carrying fluid in and out of the recirculation. Based on the results of these experiments, I am able to confirm that, at least in this controlled environment, basic geometry has a profound effect on the mixing effectiveness of a recirculation. I demonstrate radically increased stirring and mixing in the unsteady hyperbolic flow as compared to steady flows and flows without hyperbolic points. Recirculations are ubiquitous in the world ocean; they occur on a variety of scales, in many different configurations, and at all depths. Some of these configurations involve hyperbolic points, while others do not. Chaotic advection via lobe exchange may be an important component of the mixing at multiple locations in the ocean where hyperbolic recirculation geometries exist.
by Heather E. Deese.
S.M.
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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.
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SILVA, 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 textAbstract:
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Previous issue date: 2009Coordenação 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
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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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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 textAbstract:
A contourite drift complex on the J-Anomaly Ridge (JAR) and Southeast Newfoundland Ridge (SENR), offshore eastern Canada, records an extensive archive of North Atlantic circulatory and sedimentary dynamics formed under the influence of the Deep Western Boundary Current (DWBC). Seismic-reflection profiles constrained by drill sites from IODP Expedition 342 are used to map the spatial and temporal distribution of contourite sedimentation and to evaluate the Cenozoic history of the DWBC within a preexisting climatic framework. This study indicates three phases of sedimentation termed here Pre-Contourite-Drift Phase (~115-50 Ma), Active-Contourite-Drift Phase (~50-2.6 Ma), and Post-Contourite-Drift Phase (~2.6-0 Ma). Bottom current controlled sedimentation began at the boundary between Pre-Contourite-Drift Phase and Active-Contourite-Drift Phase (~50 Ma), and correlates to a long-term global cooling trend that initiated at the end of the Early Eocene Climatic Optimum. Within the Active-Contourite-Drift Phase at ~30 Ma depocenters shifted deeper and current energy and focus is interpreted to have increased in association with global oceanographic change at the Eocene-Oligocene transition. The beginning of Post-Contourite-Drift Phase sedimentation (~2.6 Ma) marks a shift in bottom current path towards shallower water depths, and corresponds with the onset of Northern Hemisphere ice sheets. These events of circulatory reorganization correlate with other North Atlantic seismic stratigraphic studies, suggesting that these events occurred throughout the North Atlantic. An improved understanding of long-term (>1000000 yr) dynamics of North Atlantic circulation in response to significant reorganization of Cenozoic climate provides important context towards refining models and prediction of oceanic response to contemporary climate change.Master of Science
Books on the topic "Western boundary current instability"
1
Pickart, Robert S. Hydrographic data from Endeavor 214: A study of the Gulf Stream - Deep Western Boundary Current crossover. Woods Hole, Mass: Woods Hole Oceanographic Institution, 1992.
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2
Levy-Ryan, Ellen. Moored current meter and temperature-pressure recorder measurements from the western North Atlantic (high energy benthic boundary layer and abyssal circulation experiments 1983-1984): Volume XXXIX. Woods Hole, Mass: Woods Hole Oceanographic Institution, 1986.
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3
Jiménez, Hernán Eduardo García. On the large-scale characteristics, fluxes, and variability of the North Atlantic Deep Water and its deep western boundary current deduced from nutrient and oxygen data. 1996.
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Jiménez, Hernán Eduardo García. On the large-scale characteristics, fluxes, and variability of the North Atlantic Deep Water and its deep western boundary current deduced from nutrient and oxygen data. 1996.
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Uva, Christian. Sergio Leone. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190942687.001.0001.
Full textAbstract:
Spectacle, myth, fable. These are the main categories that have traditionally defined Sergio Leone’s cinematic production, but it is necessary to underline how much they are fueled by a profound, layered political interest. Leone’s cinema bears witness to a critical outlook both on the subjects it showcases and on its representational means. Far from any militancy and escaping ideological classifications, Leone’s perspective is problematic and unreconciled: it is grounded in the coexistence of different elements in a state of perennial productive tension and instability. The adjective “political” takes on a deeper meaning when it is used to denote the director’s ability to narrate and interpret key aspects of Italian national identity and history. The abstract quality of his production relies on an original use of different genres, particularly sword-and-sandal and the Spaghetti Western, which allowed Leone to insert frequent symbolic references to both history and then-current events. On the stylistic level, his constant disobedience to classical models and his need to revolutionize forms were motivated by an authorial desire to make films politically, though still within a conception of cinema as an industrial spectacle.
Book chapters on the topic "Western boundary current instability"
1
Toba, Y., K. Hanawa, H. Kawamura, Y. Yano, and Y. Kurasawa. "Horizontal Processes Involved in the Formation of Sea Surface Temperature Near a Western Boundary Current." In The Ocean Surface, 571–76. Dordrecht: Springer Netherlands, 1985. http://dx.doi.org/10.1007/978-94-015-7717-5_77.
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Clarke, John E. Hughes, Dennis W. O’Leary, and David J. W. Piper. "Western Nova Scotia Continental Rise: Relative Importance of Mass Wasting and Deep Boundary-Current Activity." In Geologic Evolution of Atlantic Continental Rises, 266–81. Boston, MA: Springer US, 1992. http://dx.doi.org/10.1007/978-1-4684-6500-6_10.
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Kelly, Kathryn A., and Shenfti Dong. "The Relationship of Western Boundary Current Heat Transport and Storage to Midlatitude Ocean-Atmosphere Interaction." In Earth's Climate, 347–63. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/147gm19.
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Sommeria, J., and E. Thivolle-Cazat. "An experimental investigation of a boundary current instability." In Shallow Flows, 23–30. Taylor & Francis, 2004. http://dx.doi.org/10.1201/9780203027325.ch2.
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He, Zhigang, Kewei Lyu, and Qi Quan. "The South China Sea Western Boundary Current." In Regional Oceanography of the South China Sea, 77–99. WORLD SCIENTIFIC, 2020. http://dx.doi.org/10.1142/9789811206917_0004.
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Piola, Alberto R., and Ricardo P. Matano. "Ocean Currents: Atlantic Western Boundary—Brazil Current/Falkland (Malvinas) Current." In Encyclopedia of Ocean Sciences, 414–20. Elsevier, 2019. http://dx.doi.org/10.1016/b978-0-12-409548-9.10541-x.
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Yinian, Liu, and Jia Fu. "THE EFFECTS OF SHELF TOPOGRAPHY ON THE BOUNDARY CURRENT INSTABILITY." In Frontiers of Fluid Mechanics, 719–24. Elsevier, 1988. http://dx.doi.org/10.1016/b978-0-08-036232-8.50129-8.
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"Site 1124: Rekohu Drift—from the K/T Boundary to the Deep Western Boundary Current." In Proceedings of the Ocean Drilling Program, 181 Initial Reports. Ocean Drilling Program, 2000. http://dx.doi.org/10.2973/odp.proc.ir.181.108.2000.
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HE, ZHIGANG, and DONGXIAO WANG. "SURFACE PATTERN OF THE SOUTH CHINA SEA WESTERN BOUNDARY CURRENT IN WINTER." In Advances in Geosciences, 99–107. World Scientific Publishing Company, 2009. http://dx.doi.org/10.1142/9789812836168_0008.
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"Site 1123: North Chatham Drift—a 20-Ma Record of the Pacific Deep Western Boundary Current." In Proceedings of the Ocean Drilling Program, 181 Initial Reports. Ocean Drilling Program, 2000. http://dx.doi.org/10.2973/odp.proc.ir.181.107.2000.
Full textConference papers on the topic "Western boundary current instability"
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Cronin, Meghan F., Meghan F. Cronin, Meghan F. Cronin, Meghan F. Cronin, Meghan F. Cronin, Meghan F. Cronin, Meghan F. Cronin, et al. "Monitoring Ocean - Atmosphere Interactions in Western Boundary Current Extensions." In OceanObs'09: Sustained Ocean Observations and Information for Society. European Space Agency, 2010. http://dx.doi.org/10.5270/oceanobs09.cwp.20.
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Campbell, L. J. "Nonlinear dynamics of Rossby waves in a western boundary current." In ADVANCES IN FLUID MECHANICS 2006. Southampton, UK: WIT Press, 2006. http://dx.doi.org/10.2495/afm06045.
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Ceccopieri, Wellington, and Ilson C. A. da Silveira. "Is the Vertical Variability of the Ocean in Santos Bight, Brazil, Dominated by the Western Boundary Current Meanders?" In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-84058.
Full textAbstract:
The Brazil Current (CB) flows southwestward as vertically stratified and organized western boundary jet in the Brazilian shelf-break region ranging from 20–40° S, where the CB’s mass transport grows vertically. This geographical band show intense mesoescale activity due to passageway of eddies and meanders, superimposed over oceanic large-scale recirculation features which influence the oceanic circulation in the Santos Bight Pre-salt cluster area 300 km offshore. Based on 2-year observed data series of an oceanographic mooring array at Lula Field, and based on repeated hydrographic data (seawater temperature, salinity and N2 profiles) we used statistical and dynamical orthogonal modes in order to approach the local vertical current profile variability. We verified that it is 85 % explained by EOF-1. This variability is essentially of 1st baroclinic mode. Great part of it occupies the first 400–600 m water depth, with no predominant direction. We also found remarkable water column seasonal stratification. Albeit of relative weaker mean flows (0.1–0.2 m s−1), the study area is eddy dominated which are geostrophically adjusted to the 1st baroclinic mode. Furthermore, we observed that the significant directional variability over the São Paulo Plateau occurs far away from the mean current jets that flow parallel to the continental shelf-break geometry.
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Zhigang He and Dandan Sui. "Remote sensing and validation of the South China Sea western boundary current in December 2003, 2004 and 2005." In 2010 Second IITA International Conference on Geoscience and Remote Sensing (IITA-GRS 2010). IEEE, 2010. http://dx.doi.org/10.1109/iita-grs.2010.5602670.
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Chen, Chen, and Masashi Kashiwagi. "Ship Routing Based on the Kuroshio Current." In ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/omae2017-61606.
Full textAbstract:
As a strong western-boundary current, the Kuroshio Current has significant effects on the ship navigation in the East China Sea (ECS). To quantitatively know more about its influence, we present simulations of the ocean current in the North Pacific Ocean using the well-known Princeton Ocean Model (POM). The high-resolution current distributions could be applied to conduct numerical simulations of the ship navigation, which utilized a ship maneuvering model known as the Mathematical Maneuvering Group (MMG). Calculation of a container ship as well as a training ship have been conducted. The simulation results of both ships can show the significant effects of ocean currents on ship’s drifting as well as speed change, which could be used to optimize cost of both fuel and time by properly utilizing the current in ship routing.
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Matlis, Eric H., and Thomas C. Corke. "Quantitative Hot-Wire Measurements in Supersonic Boundary Layers." In ASME/JSME 2003 4th Joint Fluids Summer Engineering Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/fedsm2003-45080.
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Mean and time-resolved measurements in a supersonic boundary layer were performed in the Mach 3.5 quiet tunnel facility at the NASA Langley Research Center. This facility uses an annular bleed suction system to remove the turbulent boundary layer, thus reducing the disturbance intensities in the measurement region. A frequency-compensatedconstant current hot-wire anemometer was used to obtain fluctuation data in the boundary layer of a sharp cone at zero angle of attack. The hotwire was calibrated against the mean mass-flux profiles provided by solutions of the similarity profiles for compressible Blasius flow. A stability analysis code provided by Langley was used to solve parabolized stability equations to provide predictions of the most amplified wave-numbers, frequencies, and N-factors for the Tollmien-Schlicting instability. The results from these computations are compared to the experimental measurements performed with the anemometer. In addition, these measurements are compared to spectra obtained in high-disturbance conditions with the bleed system turned off.
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Shao, Yan-Lin, and Jens Bloch Helmers. "Numerical Analysis of Second-Order Wave Loads on Large-Volume Marine Structures in a Current." In ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/omae2014-24586.
Full textAbstract:
A time-domain Higher-Order Boundary Element Method (HOBEM) based on cubic shape functions for second-order wave-current-body interaction developed by Shao & Faltinsen [1] is further refined by investigating the feasibility of adopting the unstructured meshes on the free surface and body surfaces from an open source mesh generator [2]. When the steady local flow effect is considered in the time-domain boundary-value-problem formulation, the advection terms in the free surface are part of the sources of numerical instability. In this paper, the advection terms are taken care of in an implicit way in a 4th order Runge-Kutta scheme with much better stability. Some numerical examples extensively studied in the literature are studied in order to validate the present numerical model.
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Valverde, J., and G. van der Heijden. "Instability of a Whirling Conducting Rod in the Presence of a Magnetic Field: Application to the Problem of Space Tethers." In ASME 2005 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/detc2005-84845.
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We study the effect of a magnetic field on the behaviour of a slender conducting elastic structure subject to end forces. Both statical (buckling) and dynamical (whirling) instability are considered and we also compute post-buckling configurations. The theory used is the geometrically exact Cosserat rod theory. We consider two types of boundary conditions: the traditional welded boundary conditions (for tether-like applications) and a novel set of boundary conditions that give rise to exact helical post-buckling solutions. Our results are relevant for current designs of electrodynamic space tethers and potentially for future applications in nano- and molecular wires.
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Ghoshal, Ritwik, Anurag Yenduri, Aziz Ahmed, Zhuo Chen, Wenping Wang, Anis Hussain, Rajeev K. Jaiman, and Xudong Qian. "Instability of Mooring Cables in Presence of Ice-Load." In ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/omae2016-54713.
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Station keeping system for arctic floaters such as mooring cables requires an innovative engineering design coupled with a detailed investigation on its resistance against the impact loading. The ice-induced vibration, together with the wave and current actions, imposes a strong demand on the mooring cable design. However, in present industry practice, the mathematical models/software used in designing the mooring cables for offshore structures use linear strain theory. In this paper, an analytical modal based procedure for underwater submerged cable considering its geometric nonlinearity is presented. Introducing geometric nonlinearity into the modal procedure enables coupling between different modes, which is not included in the standard the linear analysis of integrated mooring system. In the present analysis, the second in-plane and first two out-of-plane modes are considered to highlight the effect of geometric nonlinearity near the 2:1 internal resonance phenomena of underwater mooring cables. The differential equation for cable is solved using a modal decomposition method considering second-order terms of the finite strain tensor. A simply supported boundary condition is assumed at both ends of the cable. A unidirectional wave loading is considered and thereby, the floater will have two translational motions, i.e., surge and heave. The floater motions will cause a support excitation at the pinned connection between the floater and mooring. This phenomenon is modelled as a base excitation at the top support point of the mooring cable. The support excitation frequency is chosen to be close to the natural frequency of the second in-plane mode. Therefore, the in-plane mode is excited directly. Ice load is applied at the support from an out-of-plane direction as a pulse load which may come from the ice impact and/or breaking. So, the out-of-plane mode is excited parametrically. It is observed that the out-of-plane mode responses show instability under certain base excitation amplitude, i.e., the responses due to the pulse load from the ice impact never decay. This instability in the responses may lead to the fatigue failure of the mooring cables. It is observed that this instability in the responses arises from the modal interaction between the different modes, i.e., autoparametric excitation, which the linear analysis is unable to capture. Numerous simulations are carried out to determine the stability boundary of different out-of-plane modes for various amplitude and excitation frequency. The stability boundaries are also determined using the harmonic balance method to verify the results obtained from the modal analysis. It can be concluded from this analysis that the nonlinear coupling terms play a significant role, close to the 2:1 resonance region which can lead to an unstable response of the mooring cables in the presence of ice loads.
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Guo, Shuai, Camilo F. Silva, and Wolfgang Polifke. "Efficient Robust Design for Thermoacoustic Instability Analysis: A Gaussian Process Approach." In ASME Turbo Expo 2019: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/gt2019-90732.
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Abstract In the preliminary phase of analysing the thermoacoustic characteristics of a gas turbine combustor, implementing robust design principles is essential to minimize detrimental variations of its thermoacoustic performance under various sources of uncertainties. In the current study, we systematically explore different aspects of robust design in thermoacoustic instability analysis, including risk analysis, control design and inverse tolerance design. We simultaneously take into account multiple thermoacoustic modes and uncertainty sources from both the flame and acoustic boundary parameters. In addition, we introduce the concept of a “risk diagram” based on specific statistical descriptions of the underlying uncertain parameters, which allows practitioners to conveniently visualize the distribution of the modal instability risk over the entire parameter space. Throughout the present study, a machine learning method called “Gaussian Process” (GP) modeling approach is employed to efficiently tackle the challenge posed by the large parameter variational ranges, various statistical descriptions of the parameters as well as the multifaceted nature of robust design analysis. For each of the investigated robust design tasks, we propose an efficient solution strategy and benchmark the accuracy of the results delivered by GP models. We demonstrate that GP models can be flexibly adjusted to various tasks while only requiring one-time training. Their adaptability and efficiency make this modeling approach very appealing for industrial practices.
Reports on the topic "Western boundary current instability"
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Watts, D. R., Kathleen A. Donohue, and Arlene Guest. Western Boundary Current Systems Virtual Poster Session. Fort Belvoir, VA: Defense Technical Information Center, September 2001. http://dx.doi.org/10.21236/ada624673.
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Pickart, Robert S. Studies of the Gulf Stream and Deep Western Boundary Current Where They Cross at Cape Hatteras. Fort Belvoir, VA: Defense Technical Information Center, May 1996. http://dx.doi.org/10.21236/ada310465.
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Jahnke, R. A. Burial, remineralization and utilization of organic matter at the seafloor under a strong western boundary current. Annual progress report, 1 May 1993--30 April 1994. Office of Scientific and Technical Information (OSTI), December 1993. http://dx.doi.org/10.2172/374123.
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Jahnke, R. A. Burial, remineralization and utilization of organic matter at the sea floor under a strong western boundary current. Final report, May 1, 1992--April 30, 1995. Office of Scientific and Technical Information (OSTI), August 1995. http://dx.doi.org/10.2172/132688.
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