Academic literature on the topic 'Western boundary current separation'
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Journal articles on the topic "Western boundary current separation"
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Baines, Peter G., and Roger L. Hughes. "Western Boundary Current Separation: Inferences from a Laboratory Experiment." Journal of Physical Oceanography 26, no. 12 (December 1996): 2576–88. http://dx.doi.org/10.1175/1520-0485(1996)026<2576:wbcsif>2.0.co;2.
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Sakamoto, Toshihiro. "Western Boundary Current Separation Caused by a Deep Countercurrent." Geophysical & Astrophysical Fluid Dynamics 96, no. 3 (January 2002): 179–99. http://dx.doi.org/10.1080/03091920290020977.
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Munday, David R., and David P. Marshall. "On the Separation of a Barotropic Western Boundary Current from a Cape." Journal of Physical Oceanography 35, no. 10 (October 1, 2005): 1726–43. http://dx.doi.org/10.1175/jpo2783.1.
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Abstract The problem of western boundary current separation is investigated using a barotropic vorticity model. Specifically, a boundary current flowing poleward along a boundary containing a cape is considered. The meridional gradient of the Coriolis parameter (the β effect), the strength of dissipation, and the geometry of the cape are varied. It is found that 1) all instances of flow separation are coincident with the presence of a flow deceleration, 2) an increase in the strength of the β effect is able to suppress flow separation, and 3) increasing coastline curvature can overcome the suppressive β effect and induce separation. These results are supported by integrated vorticity budgets, which attribute the acceleration of the boundary current to the β effect and changes in flow curvature. The transition to unsteady final model states is found to have no effect upon the qualitative nature of these conclusions.
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Cessi, Paola. "Laminar separation of colliding western boundary currents." Journal of Marine Research 49, no. 4 (November 1, 1991): 697–717. http://dx.doi.org/10.1357/002224091784995738.
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Adamec, David. "Western Boundary Current Separation Sensitivity Studies Using a Quasigeostrophic Ocean Model." Journal of Physical Oceanography 27, no. 5 (May 1997): 798–809. http://dx.doi.org/10.1175/1520-0485(1997)027<0798:wbcsss>2.0.co;2.
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Kiss, Andrew E. "Potential vorticity "crises", adverse pressure gradients, and western boundary current separation." Journal of Marine Research 60, no. 6 (November 1, 2002): 779–803. http://dx.doi.org/10.1357/002224002321505138.
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Schaeffer, Amandine, Moninya Roughan, and Bradley D. Morris. "Cross-Shelf Dynamics in a Western Boundary Current Regime: Implications for Upwelling." Journal of Physical Oceanography 43, no. 5 (May 1, 2013): 1042–59. http://dx.doi.org/10.1175/jpo-d-12-0177.1.
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Abstract The cross-shelf dynamics up- and downstream of the separation of the South Pacific Ocean’s Western Boundary Current (WBC) are studied using two years of high-resolution velocity and temperature measurements from mooring arrays. The shelf circulation is dominated by the East Australian Current (EAC) and its eddy field, with mean poleward depth-integrated magnitudes on the shelf break of 0.35 and 0.15 m s−1 up- and downstream of the separation point, respectively. The high cross-shelf variability is analyzed though a momentum budget, showing a dominant geostrophic balance at both locations. Among the secondary midshelf terms, the bottom stress influence is higher upstream of the separation point while the wind stress is dominant downstream. This study investigates the response of the velocity and temperature cross-shelf structure to both wind and EAC intrusions. Despite the deep water (up to 140 m), the response to a dominant along-shelf wind stress forcing is a classic two-layer Ekman structure. During weak winds, the shelf encroachment of the southward current drives an onshore Ekman flow in the bottom boundary layer. Both the bottom velocity and the resultant bottom cross-shelf temperature gradient are proportional to the magnitude of the encroaching current, with similar linear regressions up- and downstream of the WBC separation. The upwelled water is then subducted below the EAC upstream of the separation point. Such current-driven upwelling is shown to be the dominant driver of cold water uplift in the EAC-dominated region, with significant impacts expected on nutrient enrichment and thus on biological productivity.
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Solodoch, Aviv, James C. McWilliams, Andrew L. Stewart, Jonathan Gula, and Lionel Renault. "Why Does the Deep Western Boundary Current “Leak” around Flemish Cap?" Journal of Physical Oceanography 50, no. 7 (July 1, 2020): 1989–2016. http://dx.doi.org/10.1175/jpo-d-19-0247.1.
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AbstractThe southward-flowing deep limb of the Atlantic meridional overturning circulation is composed of both the deep western boundary current (DWBC) and interior pathways. The latter are fed by “leakiness” from the DWBC in the Newfoundland Basin. However, the cause of this leakiness has not yet been explored mechanistically. Here the statistics and dynamics of the DWBC leakiness in the Newfoundland Basin are explored using two float datasets and a high-resolution numerical model. The float leakiness around Flemish Cap is found to be concentrated in several areas (hot spots) that are collocated with bathymetric curvature and steepening. Numerical particle advection experiments reveal that the Lagrangian mean velocity is offshore at these hot spots, while Lagrangian variability is minimal locally. Furthermore, model Eulerian mean streamlines separate from the DWBC to the interior at the leakiness hot spots. This suggests that the leakiness of Lagrangian particles is primarily accomplished by an Eulerian mean flow across isobaths, though eddies serve to transfer around 50% of the Lagrangian particles to the leakiness hot spots via chaotic advection, and rectified eddy transport accounts for around 50% of the offshore flow along the southern face of Flemish Cap. Analysis of the model’s energy and potential vorticity budgets suggests that the flow is baroclinically unstable after separation, but that the resulting eddies induce modest modifications of the mean potential vorticity along streamlines. These results suggest that mean uncompensated leakiness occurs mostly through inertial separation, for which a scaling analysis is presented. Implications for leakiness of other major boundary current systems are discussed.
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Pichevin, Thierry, Steven Herbette, and France Floc’h. "Eddy Formation and Shedding in a Separating Boundary Current." Journal of Physical Oceanography 39, no. 8 (August 1, 2009): 1921–34. http://dx.doi.org/10.1175/2009jpo4151.1.
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Abstract This study deals with the separation of western boundary currents within a reduced-gravity framework, and it analyzes the formation of eddies in the separation region and the conditions of their shedding into the open ocean. It shows that the separation point of the current oscillates along the coast so that the retroflected eastward current develops meanders. These meanders grow, drift westward under the influence of β, and finally hit the coastal current, which leads to the periodic formation of eddies. This study also highlights the impact by the geometrical configurations of the flow and coastline upon the existence or lack of a subsequent shedding of these eddies: a shedding occurs when no obstacle hinders the β-induced westward drift of the eddies. This happens when either (i) the current retroflects far enough beyond the tip of the coast so that, because of β, the eddies can propagate westward without being blocked, or (ii) the tilt of the coast is small enough so that the alongshore component of the β-induced velocity is enhanced and the eddies can escape from the retroflection region.
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Pérez-Brunius, Paula, Heather Furey, Amy Bower, Peter Hamilton, Julio Candela, Paula García-Carrillo, and Robert Leben. "Dominant Circulation Patterns of the Deep Gulf of Mexico." Journal of Physical Oceanography 48, no. 3 (March 2018): 511–29. http://dx.doi.org/10.1175/jpo-d-17-0140.1.
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AbstractThe large-scale circulation of the bottom layer of the Gulf of Mexico is analyzed, with special attention to the historically least studied western basin. The analysis is based on 4 years of data collected by 158 subsurface floats parked at 1500 and 2500 m and is complemented with data collected by current meter moorings in the western basin during the same period. Three main circulation patterns stand out: a cyclonic boundary current, a cyclonic gyre in the abyssal plain, and the very high eddy kinetic energy observed in the eastern Gulf. The boundary current and the cyclonic gyre appear as distinct features, which interact in the western tip of the Yucatan shelf. The persistence and continuity of the boundary current is addressed. Although high variability is observed, the boundary flow serves as a pathway for water to travel around the western basin in approximately 2 years. An interesting discovery is the separation of the boundary current over the northwestern slope of the Yucatan shelf. The separation and retroflection of the along-slope current appears to be a persistent feature and is associated with anticyclonic eddies whose genesis mechanism remains to be understood. As the boundary flow separates, it feeds into the westward flow of the deep cyclonic gyre. The location of this gyre—named the Sigsbee Abyssal Gyre—coincides with closed geostrophic contours, so eddy–topography interaction via bottom form stresses may drive this mean flow. The contribution to the cyclonic vorticity of the gyre by modons traveling under Loop Current eddies is discussed.
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.
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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.
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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.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 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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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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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.
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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).
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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.
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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.
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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.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2010.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.
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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 separation"
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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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Muslims in the West caught between rights & duties: Redefining the separation of church & state. Warren Center, PA: Shangri-La Publications, 2002.
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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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Aldeeb, Sami A. Aldeeb Sami A., and Sami Awad Aldeeb Abu-Sahlieh. Muslims in the West: Redefining the Separation of Church & State. Shangri-La Publications, 2002.
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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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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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Hempton, David, ed. Organizing Concepts and ‘Small Differences’ in the Comparative Secularization of Western Europe and the United States. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198798071.003.0019.
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This chapter offers a long-range historical perspective on the comparative secularization trajectories of Western Europe and the United States, built around the idea of ‘small differences’ which, over time, produce different patterns. The main categories of analysis include the separation of church and state, the democratization of Christianity and the role of free markets, the relationship between religion and political culture, the organizational characteristics of religious congregations, the contrasting roles played by social elites and a correspondingly different relationship between religion and popular culture, the differential importance of evangelical Christianity and the impact of immigration. The chapter finishes with a plea for more attention to the social historical dimensions of transatlantic comparison, including how churches were funded, the impact of fertility rates and generational transmission, and a preliminary look at current trends and future projections.
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Bryant, Jan. Artmaking in the Age of Global Capitalism. Edinburgh University Press, 2019. http://dx.doi.org/10.3366/edinburgh/9781474456944.001.0001.
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What strategies are visual artists and filmmakers using to criticise the social and economic conditions shaping our particular historical moment? This question is answered by considering the methods and political implications of artists or filmmakers working in a contemporary western art context today. Leading into extended analyses of works by Frances Barrett, Claire Denis, Angela Brennan, and Alex Monteith, the book considers two forces that have informed contemporary artmaking: the economic conditions that began changing social realities from the 1970s forward; and the current tendency of the political aesthetic to move away from direct political content or didacticism to a concern for the sensate effects of materials. This is framed by Jacques Rancière’s ‘distribution of the sensible’ and Walter Benjamin’s historical materialism. As historical ground for understanding the contemporary condition, Artmaking in the Age of Global Economics pays particular attention to the divisions that opened up between progressive writers, theorists and artists in the late 20th century. Suggesting an alternative approach to understanding art’s historical antecedents, it avoids received art-historical narratives or canonical figures, refuting both the autonomy of art as well as the separation of artist from the work they produce. It locates, instead, contemporary art in a worldly context of responsibility that opens up to an ethics of practice. [211]
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Jadoul, Michel, Laura Labriola, and Eric Goffin. Viral infections in patients on dialysis. Edited by Jonathan Himmelfarb. Oxford University Press, 2015. http://dx.doi.org/10.1093/med/9780199592548.003.0271.
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From the early days of hemodialysis, viral hepatitis has been recognized as common in dialyzed patients.The prevalence and incidence of HBV infection have decreased markedly over the last decades in HD units. Still, the infectivity of HBV is very high. Vaccinating HD patients, preferably prior to starting dialysis, together with the strict application of hygienic precautions and adequate screening of blood donors remains required, together with the segregation of infective (HBV+) patients in a separate dialysis ward. The level of aminotransferases is markedly lower in HD patients than in the general population: any level above the normal range should thus trigger the suspicion of acute hepatitis (viral or not). The treatment of HBV infection in HD patients is rarely required, unless they are scheduled for a kidney transplant.Screening for HCV infection usually relies on a modern ELISA test. The prevalence and incidence of HCV infection in HD patients has also decreased substantially but remains higher than in the general population. The risk of post-transfusional HCV is currently extremely low, at least in western countries. The actual application of basic hygienic precautions is crucial if nosocomial transmission of HCV is to be prevented. These include optimal hand hygiene practices (hydroalcoholic solution use before contact with patient and after gloves withdrawal), the systematic wearing of gloves, to be changed between patients/stations, an adequate separation of the clean and contaminated items and circuits within the HD unit, and regular cleaning/disinfection of potentially contaminated surfaces. The necessity and usefulness to isolate HCV positive patients in a separate dialysis ward has not been demonstrated and is not recommended by current KDIGO guidelines. The field of the treatment of HCV infection is changing rapidly with many orally active drugs, some of which can be used even in dialysis patients.
Book chapters on the topic "Western boundary current separation"
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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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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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"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.
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Gerhard, Hafner, and Novak Gregor. "Part IV Treaty Application, 16 State Succession in Respect of Treaty Relationships." In The Oxford Guide to Treaties. Oxford University Press, 2020. http://dx.doi.org/10.1093/law/9780198848349.003.0017.
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This chapter returns to the international frame, asking how treaties apply in cases of disruption to the international legal order — State succession — a topic addressed by the 1978 Vienna Convention on Succession of States in respect of Treaties (VCSST). The present state of affairs relating to treaty succession suggests that only some of the VCSST’s provisions can serve as a reliable guide to the current State of customary international law (e.g. Article 11’s continuation of all boundary regimes, Article 15’s ‘moving treaty boundaries’ rule). Others constitute progressive development of international law (e.g. Article 31 in cases of incorporation; Article 34 in cases of separation). In any case, modern treaty succession distinguishes not only among the different cases of State succession, such as merger or dismemberment, but also among specific categories of treaties that are subject to different rules or principles. It is therefore difficult to identify a generally applicable legal regime of treaty succession.
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Deane-Drummond, Celia E. "Taking Soundings." In Shadow Sophia, 1–15. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198843467.003.0001.
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This chapter introduces themes that are important throughout this work. Augustine’s doctrine of original sin continues to hold sway for many theologians and the chapter briefly discusses recent works that have taken his thinking seriously in the light of evolution. The chapter also begins to map the relationships between sin, evil, natural evil, and moral evil. This blurring between natural and moral evil represents the most recent example of why an adequate understanding of sin that takes account of humanity’s embedded relationship with the natural world is so important. The chapter begins with a very brief discussion of shame, conscience, and evolutionary explanations of religion in early human societies. Following this is a brief review of Western theological explanations for the persistence of evil through a review of current literature on original sin. The chapter then argues, following traditional sources, that sin is worth exploring in order to understand virtue; in other words, an exploration of vices helps to elucidate the meaning of virtues. The chapter then comments on the common dichotomy between natural and moral evil and argues for a much greater blurring of that boundary in thinking through the biocultural origins of sin and guilt. J.M. Coetze’s novel Disgrace captures the complex and ambiguous interlacing of human sin and animality. The rest of the present volume intends to show more clearly what that blurring signifies as well as the distinctive nature of human sin and its symbolic character, which has semiotic properties amounting to a grossly distorted form of wisdom, shadow sophia.
Conference papers on the topic "Western boundary current separation"
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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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Fichte, Lars Ole, and Markus Clemens. "A Method combining Boundary Integral Equation and Separation Method Applied to Plane Eddy Current Problems." In 2007 International Symposium on Electromagnetic Compatibility. IEEE, 2007. http://dx.doi.org/10.1109/elmagc.2007.4413558.
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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.
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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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Prapamonthon, Prasert, Bo Yin, and Guowei Yang. "Extra-Low Reynolds Number Vane Separation Using Immersed Boundary Method." In ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/ajkfluids2019-5077.
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Abstract Nowadays, mini unmanned aerial vehicles (MUAVs) and micro air vehicles (MAVs) are not only beneficially used as aviation models but also as modern drones for military missions and other civilian applications. Hence, research and development of propulsion sources for MUAVs and MAVs dynamically increase with a future trend of high performance, but low energy consumption. Certainly, using micro and ultra-small-size gas turbine is a good option for the propulsion source. To achieve ideal flight of MUAVs and MAVs powered by micro and ultra-small-size gas turbines under this trend, understanding of flow phenomena at wide ranges of Reynolds number is essential. This research presents a 2D numerical study of characteristics of laminar flow separation and the trailing-edge vortex on a turbine vane at extra-low Reynolds numbers (Res) i.e. Re = 1800 and 3600, and three rotational angles (α) i.e. α = 0°, 15° and 30° using immersed boundary method (IBM). With this method, the problem of incompressible flow is addressed by a sharp interface IBM. Numerical results indicate that IBM can characterize phenomena of laminar separation flow, which usually happens on the turbine airfoil when laminar boundary layer cannot overcome adverse pressure gradients and viscous effects. To our current knowledge, this may be the first research to study flow behavior at such low Res for gas turbine vanes using IBM. Even though it is now not common to operate micro and ultra-small-size gas turbines under these conditions, it is important to know how aerodynamic performance may be if micro and ultra-small-size gas turbines need to run under such conditions in the near future.
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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.
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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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Otto, William, Douwe Rijpkema, and Guilherme Vaz. "Viscous-Flow Calculations on an Axial Marine Current Turbine." In ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/omae2012-83452.
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In this paper, the flow over a marine current turbine is studied. As a test case, the benchmark turbine published in [1, 2] is selected. A bibliography review shows a variety of numerical methods applied to this specific turbine, of which a viscous-flow RANS approach seems to be the best suitable for simulations over a broad range of inflow conditions. Therefore, MARIN’s RANS solver ReFRESCO is used to study the flow over this turbine. ReFRESCO results show a good agreement with the experiments, the calculated results and associated uncertainties overlapping the model-tests results. A numerical procedure is followed to estimate these calculation uncertainties, including an estimation for the numerical, domain and geometrical uncertainties. The flow-field analysis reveals significant viscous effects. Large separation zones at the suction side of the blade are seen in the model-scale results. At model scale, the turbulence level indicates that the turbine is operating in the transitional regime between laminar and turbulent flow, leading to early flow separation. Calculations at full scale show a large scale effect. The separation zones present at model scale are significantly smaller at full scale, resulting in a higher power production and axial loading. This is explained by the fully-turbulent boundary layer.
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Xu, Xiaofei, Huu Duc Vo, Njuki Mureithi, and Xue Feng Zhang. "Turbulent Boundary Layer Separation Control by Using DBD Plasma Actuators: Part II—Numerical Model Validation and Parametric Study." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-37325.
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Following an experimental investigation into suppression of a 2-D turbulent boundary layer separation with dielectric barrier discharge (DBD) plasma actuators, the present work investigates the concept numerically. The purpose is to develop and validate a simulation tool that captures the flow physics and carry out a parametric study of the concept at flow regimes beyond the current flow control capability of plasma actuators of conventional strength. First, a plasma actuator model is integrated into the commercial computational fluid dynamics (CFD) code ANSYS CFX to simulate the effects of plasma actuation. This computational tool is validated through comparison of results with the experimental results for pulsed actuation in quiescent air and for the control of a turbulent boundary layer separation at low flow velocities. It is shown that CFX with an integrated plasma model can capture the main experimentally observed effects of DBD actuators on turbulent boundary layer separation. Subsequently, this numerical approach is used, with increased plasma actuator strength, to study the influence of different actuation parameters (e.g., actuation location, direction and frequency) on suppression of turbulent boundary layer separation at higher flow velocities.
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Uzol, Og˘uz, Xue Feng Zhang, Alex Cranstone, and Howard Hodson. "Investigation of Unsteady Wake-Separated Boundary Layer Interaction Using Particle-Image-Velocimetry." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-28099.
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The current paper presents an experimental investigation of the interaction between unsteady wakes and the separated boundary layer on the suction side of an ultra-high-lift low-pressure turbine airfoil. Two-dimensional Particle Image Velocimetry (PIV) measurements of the unsteady boundary layer over the T106C LP turbine profile were performed in a low speed linear cascade facility, at selected phases of passing wakes. The wakes are created by moving cylindrical bars across the inlet of the test section. Various phenomena were investigated such as separation and transition characteristics, vortex structures within the unsteady boundary layer, their interaction and effects on the transition process, the corresponding vortex shedding mechanisms and the unsteady behaviour of the separation bubble due to the wake- boundary layer interaction. The current measurements suggest that rollup vortices are generated as the wake approaches the separated shear layer on the suction surface before the wake centerline starts impinging on the blade. At this instant, the bubble is sufficiently high for the free shear layer to roll up into a vortex and the incoming wake is highly distorted (strained) due to the velocity field within the blade passage, and the turbulence distribution within the wake is not symmetrical. Vortices within the boundary layer, identified using the swirl strength distributions calculated from the eigenvalues of the velocity gradient tensor, seem to be coalescing and forming bigger scale structures, which in turn break up into smaller but higher swirl strength eddies. In between the passing wakes, the separation bubble grows in both in height and length, trying to return to its steady state shape.
Reports on the topic "Western boundary current separation"
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Cessi, Paola. Separation of Western Boundary Currents. Fort Belvoir, VA: Defense Technical Information Center, October 1992. http://dx.doi.org/10.21236/ada256516.
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2
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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3
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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4
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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5
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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