285 research outputs found

    Zonal jets in the Southern Ocean: a semi-analytical model based on scale separation

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    A reduced-order semi-analytic model of multiple zonal jets in the Southern Ocean is proposed based on the statistical approach and scale decomposition. By introducing two dominant scales in the vorticity equation, the model describes the large-scale and mesoscale dynamics using the explicit momentum dissipation in the horizontal and vertical directions. For validation and physical insights, the results of the reduced-order model are compared with solutions of two eddy-resolving ocean models: i) a realistic primitive-equation HYCOM (HYbrid Coordinate Ocean Model) simulation of the Southern Ocean and ii) an idealized quasi-geostrophic model of a shear-driven channel flow

    Inferring the Pattern of the Oceanic Meridional Transport from the Air-Sea Density Flux

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    The article of record as published may be found at http://dx.doi.org/10.1175/2008JPO3748.1An extension of Walin’s water mass transformation analysis is proposed that would make it possible to assess the strength of the adiabatic along-isopycnal component of the meridional overturning circulation (MOC). It is hypothesized that the substantial fraction of the adiabatic MOC component can be attributed to the difference in subduction rates at the northern and southern outcrops of each density layer—the “push–pull” mechanism. The GCM-generated data are examined and it is shown that the push–pull mode accounts for approximately two-thirds of the isopycnal water mass transport in the global budget and dominates the Atlantic transport. Much of the difference between the actual interhemispheric flux and the push–pull mode can be ascribed to the influence of the Antarctic Circumpolar Current, characterized by the elevated (at least in the GCM) values of the diapycnal transport. When the diagnostic model is applied to observations, it is discovered that the reconstructed MOC is consistent, in terms of the magnitude and sense of overturning, with earlier observational and modeling studies. The findings support the notion that the dynamics of the meridional overturning are largely controlled by the adiabatic processes—time-mean and eddy-induced advection of buoyancy

    On the Utility and Disutility of JEBAR

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    The usefulness of the concept of JEBAR, the joint effect of baroclinicity and relief, in large-scale ocean dynamics is critically analyzed. The authors address two questions. Does the JEBAR term properly characterize the joint impact of stratification and bottom topography on the ocean circulation? Do estimates of the JEBAR term from observational data allow reliable diagnostic calculations? The authors give a negative answer to the first question. The JEBAR term need not give a true measure of the effect of bottom relief in a stratified ocean. A simple two-layer model provides examples. As to the second question, it is demonstrated that the large-scale pattern of the transport streamfunction is captured by the smoothed solution, especially with the Mellor et al. formulation of the JEBAR term. However, the calculated velocity field is very noisy and the relative errors are large

    On latency of multiple zonal jets in the oceans

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    Author Posting. © Cambridge University Press, 2011. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of Fluid Mechanics 686 (2011): 534-567, doi:10.1017/jfm.2011.345.Most of the nearly zonal, multiple, alternating jets observed in the oceans are latent, that is, their amplitudes are weak relative to the ambient mesoscale eddies. Yet, relatively strong jets are often observed in dynamical simulations. To explore mechanisms controlling the degree of latency, we analyse solutions of an idealized, eddy-resolving and flat-bottom quasigeostrophic model, in which dynamically generated mesoscale eddies maintain and interact with a set of multiple zonal jets. We find that the degree of the latency is controlled primarily by the bottom friction: the larger the friction parameter, the more latent are the jets; and the degree of the latency is substantial for a realistic range of the oceanic bottom friction coefficient. This result not only provides a plausible explanation for the latency of the oceanic jets, but it may also be relevant to the prominent atmospheric multiple jets observed on giant gas planets, such as Jupiter. We hypothesize that these jets can be so strong because of the relative absence of the bottom friction. The mechanism controlling the latency in our solutions is understood in terms of the changes induced in the linear eigenmodes of the time–mean flow by varying the bottom friction coefficient; these changes, in turn, affect and modify the jets. Effects of large Reynolds numbers on the eddies, jets, and the latency are also discussed.Funding was provided: for P.B. by NSF grants OCE 0725796 and OCE 0845150, for J.T.F. by NSF grant OCE 0845150, for I.K. by NSF grant OCE 0842834, and for S.K. by the University Research Fellowship from the Royal Society. S.K. also acknowledges support from the Mary Sears Grant from the Woods Hole Oceanographic Institution.2012-09-2

    Radiating instability of nonzonal ocean currents

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997.Includes bibliographical references (leaves 192-195).by Igor V. Kamenkovich.Ph.D

    Eigenanalysis of the two-dimensional wind-driven ocean circulation problem

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    A barotropic model of the wind-driven circulation in the subtropical region of the ocean is considered. A no-slip condition is specified at the coasts and slip at the fluid boundaries. Solutions are governed by two parameters: inertial boundary-layer width; and viscous boundary-layer width. Numerical computations indicate the existence of a wedge-shaped region in this two-dimensional parameter space, where three steady solutions coexist. The structure of the steady solution can be of three types: boundary-layer, recirculation and basin-filling-gyre. Compared to the case with slip conditions (Ierley and Sheremet, 1995) in the no-slip case the wedge-shaped region is displaced to higher Reynolds numbers. Linear stability analysis of solutions reveals several classes of perturbations: basin modes of Rossby waves, modes associated with the recirculation gyre, wall-trapped modes and a “resonant” mode. For a standard subtropical gyre wind forcing, as the Reynolds number increases, the wall-trapped mode is the first one destabilized. The resonant mode associated with disturbances on the southern side of the recirculation gyre is amplified only at larger Reynolds number, nonetheless this mode ultimately provides a stronger coupling between the mean circulation and Rossby basin modes than do the wall-trapped modes

    Analysis of the barotropic model of the subtropical gyre in the ocean for finite Reynolds numbers. Part II.

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    This paper is a continuation of Part I of the suggested study of the barotropic model of the subtropical gyre for finite Reynolds numbers. The statement of the problem, the motivation of the analysis, and the description of the general properties of the solution are presented in Part I (Kamenkovich et al., 1995). Here, in Part II of the study, the detailed investigations of the peculiarities of the solution are offered. The most striking feature of the solution is the formation of a recirculation gyre in the northwest corner of the basin. To study the gyre structure for various Reynolds numbers the time-averaged fields of the stream function, and that of the relative and potential vorticity are thoroughly examined. The role of the eddies, appeared within the boundary layer, in the transfer of positive vorticity from the west coast is clarified. The analysis of the energy characteristics of the system is presented and the vorticity balance both integral and regional (within a closed streamline) is elucidated. Finally, the consistent discussion of the process of the formation of the recirculation gyre for different Reynolds numbers is suggested
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