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Rui Xin Huang - One of the best experts on this subject based on the ideXlab platform.
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Surface/Wind Driven Circulation
Reference Module in Earth Systems and Environmental Sciences, 2017Co-Authors: Rui Xin HuangAbstract:Surface motions in the upper ocean include surface waves and Wind-Driven currents. These motions are driven by surface winds. There is a wave boundary layer in the upper ocean where surface waves dominate. Below this surface boundary layer, the ocean can be conceptually separated into several layers, including the Ekman layer, the mixed layer and the main thermocline, and the thick layer below. These layers are characterized by different dynamics, but they may overlap. The most outstanding feature is the main thermocline, and it can be treated as the base of the Wind-Driven Circulation in the upper ocean.
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OCEANOGRAPHIC TOPICS | Surface/Wind Driven Circulation
Encyclopedia of Atmospheric Sciences, 2015Co-Authors: Rui Xin HuangAbstract:This article is a revision of the previous edition article by P Bogden and C A Edwards, volume 4, pp 1540–1549, © 2003, Elsevier Ltd.
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The Effects of Thermohaline Circulation on Wind-Driven Circulation in the South China Sea
Journal of Physical Oceanography, 2012Co-Authors: Guihua Wang, Rui Xin Huang, Dake ChenAbstract:AbstractThe dynamic influence of thermohaline Circulation on Wind-Driven Circulation in the South China Sea (SCS) is studied using a simple reduced gravity model, in which the upwelling driven by mixing in the abyssal ocean is treated in terms of an upward pumping distributed at the base of the upper layer.Because of the strong upwelling of deep water, the cyclonic gyre in the northern SCS is weakened, but the anticyclonic gyre in the southern SCS is intensified in summer, while cyclonic gyres in both the southern and northern SCS are weakened in winter. For all seasons, the dynamic influence of thermohaline Circulation on Wind-Driven Circulation is larger in the northern SCS than in the southern SCS. Analysis suggests that the upwelling associated with the thermohaline Circulation in the deep ocean plays a crucial role in regulating the Wind-Driven Circulation in the upper ocean.
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Ocean Circulation: Wind-Driven and Thermohaline Processes
2009Co-Authors: Rui Xin HuangAbstract:Preface 1. Description of the world oceans 2. Dynamical foundations 3. Energetics of oceanic Circulation 4. Wind-Driven Circulation 5. Thermohaline Circulation Bibliography Index.
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The Structure of the Wind-Driven Circulation in the Subtropical South Pacific Ocean*
Journal of Physical Oceanography, 1998Co-Authors: Rui Xin Huang, Bo QiuAbstract:The structure of the Wind-Driven Circulation in the subtropical South Pacific is studied using simple diagnostic and analytical models. The diagnostic calculation is based on the Levitus climatology. The analytical model is forced by observed winter mixed layer density and depth calculated from the Levitus climatology and by the surface wind stress data from the Hellerman and Rosenstein climatology. The Wind-Driven gyre in the South Pacific is relatively deep, reaching 2.4 km along the southern edge of the gyre. The gross feature of subduction obtained from both the data analysis and the analytical model is similar, with an annual ventilation rate of 21.6 Sv (Sv [ 106 m3 s21), including 18.1 Sv from vertical pumping and 3.5 Sv from lateral induction. Although the annual subduction rate in the South Pacific is comparable to that in the North Atlantic, lack of localized subduction leads to relatively weak mode water formation in the region where the East Australian Current separates from its western boundary. In addition, results from the analytical model indicate the existence of an isopycnal slope reversal in the southeastern Pacific.
S. P. Meacham - One of the best experts on this subject based on the ideXlab platform.
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Low-frequency variability in the Wind-Driven Circulation
Journal of Physical Oceanography, 2000Co-Authors: S. P. MeachamAbstract:Abstract The origins of low-frequency variability in a simple homogenous ocean model, forced by a double gyre Ekman suction, are examined numerically. It is found that irregular, large amplitude vacillations in the structure of the Circulation typify the behavior of such a model when it is forced sufficiently strongly. These oscillations are associated with order-one changes in the size and transport of the inertial reCirculation gyres that lie near the western boundary. It is suggested that this behavior arises as a result of a subcritical homoclinic bifurcation. The aperiodic solutions do not exhibit a strong tendency to linger near any of the simpler unstable solutions that were found for this system. Instead, the latter solutions appear to constrain the aperiodic solutions, confining them to a limited region of phase space for a range of values of the Munk boundary layer scale δM. The form of the aperiodic solutions suggests that there may be an interesting unstable solution that could not be isolated...
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On the stability of the Wind-Driven Circulation
Journal of Marine Research, 1998Co-Authors: Pavel Berloff, S. P. MeachamAbstract:This work examines the instabilities of steady Circulations driven by stationary single-gyre wind forcing in closed rectangular basins with different aspect ratios. The stratie ed ocean is modeled with quasi-geostrophic 1.5-layer (equivalent-barotropic) and two-layer models. As friction is reduced, a stability threshold is encountered. In the vicinity of this threshold, unstable steady states and their unstable eigenmodes are determined. The structures of the eigenmodes and their associated energy conversion terms allow us to characterize the instabilities. In each case, the loss of stability is associated with an oscillatory instability. Several different instability mechanisms are observed. Which of these is responsible for the onset of instability depends upon the basin aspect ratio and the choice of stratie cation (1.5- or two-layer). The various mechanisms include instability of the western boundary current, baroclinic instability of the main reCirculation gyre, instability of a standing meander located downstream of the main reCirculation gyre and a complex instability involving several reCirculations and the standing meander. The periods of the eigenmodes range from several months to several years depending upon the kind of instability and type of model.Additional insight into the western boundary current and baroclinic gyre instabilities is provided by an exploration of the stability of (a) the Munk boundary layer e ow in 1.5- and two-layer models in an unbounded north-south channel, and (b) an isolated baroclinic vortex on an f-plane.
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The Dynamics of a Simple Baroclinic Model of the Wind-Driven Circulation
Journal of Physical Oceanography, 1998Co-Authors: Pavel Berloff, S. P. MeachamAbstract:The authors study the dynamics of a two-layer approximation to the steadily forced baroclinic Circulation in a closed ocean basin with the aim of understanding its temporal variability and the onset of low-frequency variability. It is found that, for a range of dissipation that includes values used in a number of ocean modeling studies in the past five years, if one waits a sufficient length of time, the asymptotic behavior of the system is characterized by only a very small number of degrees of freedom. By varying the dissipation as a control parameter, the authors identify abrupt transitions in the form of the long-term Circulation exhibited by the model. One type of transition, from a time-varying Circulation dominated by two frequencies to a chaotic Circulation, is accompanied by the appearance of low-frequency variability. This constitutes an internal mechanism for the production of variability at climatological timescales. The model used is a two-layer, quasigeostrophic model forced by a steady wind stress with a uniform cyclonic curl. Dissipation is modeled by a lateral diffusion of momentum with a uniform eddy viscosity. In two sets of experiments with two internal deformation radii and layer depth ratios, the eddy viscosity is varied and the types of Circulation that result are reported. The stable steady Circulation seen in the viscous limit gives way to time-dependent Circulations of increasing temporal complexity. Spatially, the Circulations fall into two types, those dominated by large recirculating gyres in the western part of the basin and those with a strong (and strongly meandering) peripheral current reminiscent of that seen in the Black Sea. From an examination of the linear eigenmodes of the steady Circulation, the initial transition to time dependence may be characterized as a baroclinic instability of the western reCirculation gyre.
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Instabilities of a steady, barotropic, Wind-Driven Circulation
Journal of Marine Research, 1997Co-Authors: S. P. Meacham, Pavel BerloffAbstract:We explore the stability characteristics of a single, barotropic, Wind-Driven gyre as a function of the strength of the wind forcing and the size and shape of the basin. We find steady solutions for the barotropic flow in a basin driven by a steady wind stress over a range of values of the Reynolds number and the strength of the wind stress. For those solutions that are close to the stability boundary, we examine the form of the most unstable normal mode. We find that for sufficiently weak forcing, the form of the first instability seen is an instability of the western boundary current. However, for larger values of the forcing, the first instability to set in, as the Reynolds number is reduced, is centered on a standing meander that forms on the continuation of the boundary current after it has left the boundary. Both types of instability are oscillatory. There are several different modes of standing meander instability each associated with Rossby wave-like disturbances in the eastern half of the basin. Each of these modes is most unstable when its frequency is close to a resonance with a basin mode with similar spatial scales.
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Barotropic, Wind-Driven Circulation in a small basin
Journal of Marine Research, 1997Co-Authors: S. P. Meacham, Pavel BerloffAbstract:We study the asymptotic behavior (large time) of a simple, Wind-Driven, barotropic ocean model, described by a nonlinear partial differential equation with two spatial dimensions. Considered as a dynamical system, this model has an infinite-dimensional phase space. After discretization, the equivalent numerical model has a phase space of finite but large dimension. We find that for a considerable range of friction, the asymptotic states are low-dimensional attractors. We describe the changes in the structure of these asymptotic attractors as a function of the eddy viscosity of the model. A variety of different types of attractor are seen, with chaotic attractors predominating at higher Reynolds numbers. As the Reynolds number is increased, we observe a slow increase in the dimension of the chaotic attractors. Using an energy analysis, we examine the nature of the instability responsible for the Hopf bifurcation that initiates the transition from asymptotically steady states to time-dependent states.
Pavel Berloff - One of the best experts on this subject based on the ideXlab platform.
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On the stability of the Wind-Driven Circulation
Journal of Marine Research, 1998Co-Authors: Pavel Berloff, S. P. MeachamAbstract:This work examines the instabilities of steady Circulations driven by stationary single-gyre wind forcing in closed rectangular basins with different aspect ratios. The stratie ed ocean is modeled with quasi-geostrophic 1.5-layer (equivalent-barotropic) and two-layer models. As friction is reduced, a stability threshold is encountered. In the vicinity of this threshold, unstable steady states and their unstable eigenmodes are determined. The structures of the eigenmodes and their associated energy conversion terms allow us to characterize the instabilities. In each case, the loss of stability is associated with an oscillatory instability. Several different instability mechanisms are observed. Which of these is responsible for the onset of instability depends upon the basin aspect ratio and the choice of stratie cation (1.5- or two-layer). The various mechanisms include instability of the western boundary current, baroclinic instability of the main reCirculation gyre, instability of a standing meander located downstream of the main reCirculation gyre and a complex instability involving several reCirculations and the standing meander. The periods of the eigenmodes range from several months to several years depending upon the kind of instability and type of model.Additional insight into the western boundary current and baroclinic gyre instabilities is provided by an exploration of the stability of (a) the Munk boundary layer e ow in 1.5- and two-layer models in an unbounded north-south channel, and (b) an isolated baroclinic vortex on an f-plane.
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The Dynamics of a Simple Baroclinic Model of the Wind-Driven Circulation
Journal of Physical Oceanography, 1998Co-Authors: Pavel Berloff, S. P. MeachamAbstract:The authors study the dynamics of a two-layer approximation to the steadily forced baroclinic Circulation in a closed ocean basin with the aim of understanding its temporal variability and the onset of low-frequency variability. It is found that, for a range of dissipation that includes values used in a number of ocean modeling studies in the past five years, if one waits a sufficient length of time, the asymptotic behavior of the system is characterized by only a very small number of degrees of freedom. By varying the dissipation as a control parameter, the authors identify abrupt transitions in the form of the long-term Circulation exhibited by the model. One type of transition, from a time-varying Circulation dominated by two frequencies to a chaotic Circulation, is accompanied by the appearance of low-frequency variability. This constitutes an internal mechanism for the production of variability at climatological timescales. The model used is a two-layer, quasigeostrophic model forced by a steady wind stress with a uniform cyclonic curl. Dissipation is modeled by a lateral diffusion of momentum with a uniform eddy viscosity. In two sets of experiments with two internal deformation radii and layer depth ratios, the eddy viscosity is varied and the types of Circulation that result are reported. The stable steady Circulation seen in the viscous limit gives way to time-dependent Circulations of increasing temporal complexity. Spatially, the Circulations fall into two types, those dominated by large recirculating gyres in the western part of the basin and those with a strong (and strongly meandering) peripheral current reminiscent of that seen in the Black Sea. From an examination of the linear eigenmodes of the steady Circulation, the initial transition to time dependence may be characterized as a baroclinic instability of the western reCirculation gyre.
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Instabilities of a steady, barotropic, Wind-Driven Circulation
Journal of Marine Research, 1997Co-Authors: S. P. Meacham, Pavel BerloffAbstract:We explore the stability characteristics of a single, barotropic, Wind-Driven gyre as a function of the strength of the wind forcing and the size and shape of the basin. We find steady solutions for the barotropic flow in a basin driven by a steady wind stress over a range of values of the Reynolds number and the strength of the wind stress. For those solutions that are close to the stability boundary, we examine the form of the most unstable normal mode. We find that for sufficiently weak forcing, the form of the first instability seen is an instability of the western boundary current. However, for larger values of the forcing, the first instability to set in, as the Reynolds number is reduced, is centered on a standing meander that forms on the continuation of the boundary current after it has left the boundary. Both types of instability are oscillatory. There are several different modes of standing meander instability each associated with Rossby wave-like disturbances in the eastern half of the basin. Each of these modes is most unstable when its frequency is close to a resonance with a basin mode with similar spatial scales.
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The dynamics of an equivalent-barotropic model of the Wind-Driven Circulation
Journal of Marine Research, 1997Co-Authors: Pavel Berloff, Stephen P. MeachamAbstract:Various steady and time-dependent regimes of a quasi-geostrophic 1.5 layer model of an oceanic Circulation driven by a steady wind stress are studied. After being discretized as a numerical model, the quasi-geostrophic equations of motion become a dynamical system with a large dimensional phase space. We find that, for a wide range of parameters, the large-time asymptotic regimes of the model correspond to low-dimensional attractors in this phase space. Motion on these attractors is significant in determining the intrinsic time scales of the system. In two sets of experiments, we explore the dependence of solutions on the viscosity coefficient and the deformation radius. Both experiments yielded a succession of solutions with different forms of time dependence including chaotic solutions. The transition to chaos in this model occurs through a modified classical Ruelle-Takens scenario. We computed some unstable steady regimes of the Circulation and the associated fastest growing linear eigenmodes. The structure of the eigenmodes and the details of the energy conversion terms allow us to characterize the primary instability of the steady Circulation. It is a complex instability of the western boundary intensification, the western gyre and the meander between the western and central gyres. The model exhibits ranges of parameters in which multiple, stable, time-dependent solutions exist. Further, we note that some bifurcations involve the appearance of variability at climatological time scales, purely as a result of the intrinsic dynamics of the Wind-Driven Circulation.
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Barotropic, Wind-Driven Circulation in a small basin
Journal of Marine Research, 1997Co-Authors: S. P. Meacham, Pavel BerloffAbstract:We study the asymptotic behavior (large time) of a simple, Wind-Driven, barotropic ocean model, described by a nonlinear partial differential equation with two spatial dimensions. Considered as a dynamical system, this model has an infinite-dimensional phase space. After discretization, the equivalent numerical model has a phase space of finite but large dimension. We find that for a considerable range of friction, the asymptotic states are low-dimensional attractors. We describe the changes in the structure of these asymptotic attractors as a function of the eddy viscosity of the model. A variety of different types of attractor are seen, with chaotic attractors predominating at higher Reynolds numbers. As the Reynolds number is increased, we observe a slow increase in the dimension of the chaotic attractors. Using an energy analysis, we examine the nature of the instability responsible for the Hopf bifurcation that initiates the transition from asymptotically steady states to time-dependent states.
Eng Soon Chan - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic model with wave-current interaction in coastal regions
Estuarine Coastal and Shelf Science, 2004Co-Authors: Hong Zhang, Ole Secher Madsen, S. A. Sannasiraj, Eng Soon ChanAbstract:The effects of wave-current interaction on the hydrodynamics in coastal regions are investigated. A modified Grant-Madsen analytical model is incorporated into the Princeton Ocean Model (POM) to describe the wave-current interaction. The model is applied to the Singapore Straits for the prediction of tide and wind driven Circulation. The simulation results confirm that high shear velocity within the wave bottom boundary layer produces high levels of turbulence intensities. The strong turbulence intensities within the thin wave bottom boundary layer in turn affect the currents through increased bottom resistance.
Bo Qiu - One of the best experts on this subject based on the ideXlab platform.
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The Structure of the Wind-Driven Circulation in the Subtropical South Pacific Ocean*
Journal of Physical Oceanography, 1998Co-Authors: Rui Xin Huang, Bo QiuAbstract:The structure of the Wind-Driven Circulation in the subtropical South Pacific is studied using simple diagnostic and analytical models. The diagnostic calculation is based on the Levitus climatology. The analytical model is forced by observed winter mixed layer density and depth calculated from the Levitus climatology and by the surface wind stress data from the Hellerman and Rosenstein climatology. The Wind-Driven gyre in the South Pacific is relatively deep, reaching 2.4 km along the southern edge of the gyre. The gross feature of subduction obtained from both the data analysis and the analytical model is similar, with an annual ventilation rate of 21.6 Sv (Sv [ 106 m3 s21), including 18.1 Sv from vertical pumping and 3.5 Sv from lateral induction. Although the annual subduction rate in the South Pacific is comparable to that in the North Atlantic, lack of localized subduction leads to relatively weak mode water formation in the region where the East Australian Current separates from its western boundary. In addition, results from the analytical model indicate the existence of an isopycnal slope reversal in the southeastern Pacific.
