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  • 1
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    Online Resource
    Reflection and Transmission of Equatorial Rossby Waves*
    American Meteorological Society ; 2005
    In:  Journal of Physical Oceanography Vol. 35, No. 3 ( 2005-03-01), p. 363-373
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 35, No. 3 ( 2005-03-01), p. 363-373
    Abstract: The interaction of equatorial Rossby waves with a western boundary perforated with one or more narrow gaps is investigated using a shallow-water numerical model and supporting theory. It is found that very little of the incident energy flux is reflected into eastward-propagating equatorial Kelvin waves provided that at least one gap is located within approximately a deformation radius of the equator. Because of the circulation theorem around an island, the existence of a second gap off the equator reduces the reflection of short Rossby waves and enhances the transmission of the incident energy into the western basin. The westward energy transmitted past the easternmost island is further reduced upon encountering islands to the west, even if these islands are located entirely within the “shadow” of the easternmost island. A localized patch of wind forcing was also used to generate low-frequency Rossby waves for cases with island configurations representative of the western equatorial Pacific. For both idealized islands and a coastline based on the 200-m isobath, the amount of incident energy reflected into Kelvin waves depends on both the duration of the wind event and the meridional decay scale of the anomalous winds. For wind events of 2-yr duration with a meridional decay scale of 700 km, the reflected energy is 37% of the incident flux, and the energy transmitted into the Indian Ocean is approximately 10% of the incident flux, very close to that predicted by previous theories. For shorter wind events or winds confined more closely to the equator the reflected energy is significantly less.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/JPO-2691.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 2
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    Online Resource
    Anisotropic Material Transport by Eddies and Eddy-Driven Currents in a Model of the North Atlantic
    American Meteorological Society ; 2009
    In:  Journal of Physical Oceanography Vol. 39, No. 12 ( 2009-12-01), p. 3162-3175
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 39, No. 12 ( 2009-12-01), p. 3162-3175
    Abstract: This study analyzes anisotropic properties of the material transport by eddies and eddy-driven zonal jets in a general circulation model of the North Atlantic through the analysis of Lagrangian particle trajectories. Spreading rates—defined here as half the rate of change in the particle dispersion—in the zonal direction systematically exceed the meridional rates by an order of magnitude. Area-averaged values for the upper-ocean zonal and meridional spreading rates are approximately 8100 and 1400 m2 s−1, respectively, and in the deep ocean they are 2400 and 200 m2 s−1. The results demonstrate that this anisotropy is mainly due to the action of the transient eddies and not to the shear dispersion associated with the time-mean jets. This property is consistent with the fact that eddies in this study have zonally elongated shapes. With the exception of the upper-ocean subpolar gyre, eddies also cause the superdiffusive zonal spreading, significant variations in the spreading rate in the vertical and meridional directions, and the difference between the westward and eastward spreading.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2009JPO4239.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 3
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    Online Resource
    Role of Eddy Forcing in the Dynamics of Multiple Zonal Jets in a Model of the North Atlantic
    American Meteorological Society ; 2009
    In:  Journal of Physical Oceanography Vol. 39, No. 6 ( 2009-06-01), p. 1361-1379
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 39, No. 6 ( 2009-06-01), p. 1361-1379
    Abstract: Multiple zonal jets are observed in satellite data–based estimates of oceanic velocities, float measurements, and high-resolution numerical simulations of the ocean circulation. This study makes a step toward understanding the dynamics of these jets in the real ocean by analyzing the vertical structure and dynamical balances within multiple zonal jets simulated in an eddy-resolving primitive equation model of the North Atlantic. In particular, the authors focus on the role of eddy flux convergences (“eddy forcing”) in supporting the buoyancy and relative/potential vorticity (PV) anomalies associated with the jets. The results suggest a central role of baroclinic eddies in the barotropic and baroclinic dynamics of the jets, and significant differences in the effects of eddy forcing between the subtropical and subpolar gyres. Additionally, diabatic potential vorticity sources and sinks, associated with vertical diffusion, are shown to play an important role in supporting the potential vorticity anomalies. The resulting potential vorticity profile does not resemble a “PV staircase”—a distinct meridional structure observed in some idealized studies of geostrophic turbulence.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2008JPO4096.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 4
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    Online Resource
    The Response of a Weakly Stratified Layer to Buoyancy Forcing
    American Meteorological Society ; 2009
    In:  Journal of Physical Oceanography Vol. 39, No. 4 ( 2009-04-01), p. 1060-1068
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 39, No. 4 ( 2009-04-01), p. 1060-1068
    Abstract: The response of a weakly stratified layer of fluid to a surface cooling distribution is investigated with linear theory in an attempt to clarify recent numerical results concerning the sinking of cooled water in polar ocean boundary currents. A channel of fluid is forced at the surface by a cooling distribution that varies in the down-channel as well as the cross-channel directions. The resulting geostrophic flow in the central region of the channel impinges on its boundaries, and regions of strong downwelling are observed. For the parameters of the problem investigated, the downwelling occurs in a classical Stewartson layer but the forcing of the layer leads to an unusual relation with the interior flow, which is forced to satisfy the thermal condition on the boundary while the geostrophic normal flow in the interior is brought to rest in the boundary layer. As a consequence of the layer’s dynamics, the resulting long-channel flow exhibits a nonmonotonic approach to the interior flow, and the strongest vertical velocities are limited to the boundary layer whose scale is so small that numerical models resolve the region only with great difficulty. The analytical model presented here is able to reproduce key features of the previous nonlinear numerical calculations.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2008JPO3996.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 5
    Online Resource
    Online Resource
    Triad Instability of Planetary Rossby Waves
    American Meteorological Society ; 2007
    In:  Journal of Physical Oceanography Vol. 37, No. 8 ( 2007-08-01), p. 2158-2171
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 37, No. 8 ( 2007-08-01), p. 2158-2171
    Abstract: The triad instability of the large-scale, first-mode, baroclinic Rossby waves is studied in the context of the planetary scale when the Coriolis parameter is to its lowest order varying with latitude. Accordingly, rather than remain constant as in quasigeostrophic theory, the deformation radius also changes with latitude, yielding new and interesting features to the propagation and triad instability processes. On the planetary scale, baroclinic waves vary their meridional wavenumbers along group velocity rays while they conserve both frequencies and zonal wavenumbers. The amplitudes of both barotropic and baroclinic waves would change with latitude along a ray path in the same way that the Coriolis parameter does if effects of the nonlinear interaction are ignored. The triad interaction for a specific triad is localized within a small latitudinal band where the resonance conditions are satisfied and quasigeostrophic theory is applicable locally. Using the growth rate from that theory as a measure, at each latitude along the ray path of the basic wave, a barotropic wave and a secondary baroclinic wave are picked up to form the most unstable triad and the distribution of this maximum growth rate is examined. It is found to increase southward under the assumption that triad interactions do not cause a noticeable decrease in the quantity of the basic wave’s amplitude divided by the Coriolis parameter. Different barotropic waves that maximize the growth rate at different latitudes have almost the same meridional length scale, on the order of the deformation radius. With many rays starting from different latitudes on the eastern boundary and with wavenumbers on each of them satisfying the no-normal-flow condition, the resulting two-dimensional distribution of the growth rate is a complicated function of the relative relations of zonal wavenumbers or frequencies on different rays and the orientation of the eastern boundary. In general, the growth rate is largest on rays originating to the north.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/JPO3100.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 6
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    Boundary Intensification of Vertical Velocity in a β-Plane Basin
    American Meteorological Society ; 2005
    In:  Journal of Physical Oceanography Vol. 35, No. 12 ( 2005-12-01), p. 2487-2500
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 35, No. 12 ( 2005-12-01), p. 2487-2500
    Abstract: The buoyancy-driven circulation of simple two-layer models on the β plane is studied in order to examine the role of beta in determining the magnitude and structure of the vertical motions forced in response to surface heating and cooling. Both analytical and numerical approaches are used to describe the change in circulation pattern and strength as a consequence of the planetary vorticity gradient. The physics is quasigeostrophic at lowest order but is sensitive to small nonquasigeostrophic mass fluxes across the boundary of the basin. The height of the interface between the two layers serves as an analog of temperature, and the vertical velocity at the interface consists of a cross-isopycnal velocity, modeled in terms of a relaxation to a prescribed interface height, as well as an adiabatic representation of eddy thickness fluxes parameterized as lateral diffusion of interface displacement. In the numerical model the lateral eddy diffusion of heat is explicitly represented by a resolved eddy field. In the plausibly more realistic case, when the lateral diffusion of buoyancy dominates the diffusion of momentum, the major vertical velocities occur at the boundary of the basin as in earlier f-plane studies. The effect of the planetary vorticity gradient is to intensify the sinking at the western wall and to enhance the magnitude of that sinking with respect to the f-plane models. The vertical mass flux in the Sverdrup interior exactly balances the vertical flux in the region of the strong horizontal transport of the western boundary current, leaving the net flux to occur in a very narrow region near the western boundary tucked well within the western boundary current. On the other hand, if the lateral diffusion of heat is arbitrarily and unrealistically eliminated, the vertical mass flux is forced to occur in the interior. The circulation pattern is extremely sensitive to small net inflows or outflows across the basin perimeter. The cross-basin flux determines the interface height on the basin’s eastern boundary and affects the circulation pattern across the entire basin.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/JPO2832.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 7
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    The skirted island: The effect of topography on the flow around planetary scale islands
    Journal of Marine Research/Yale ; 2009
    In:  Journal of Marine Research Vol. 67, No. 4 ( 2009-07-01), p. 435-478
    Details
    In: Journal of Marine Research, Journal of Marine Research/Yale, Vol. 67, No. 4 ( 2009-07-01), p. 435-478
    Type of Medium: Online Resource
    ISSN: 0022-2402 , 1543-9542
    URL: Article
    DOI: 10.1357/002224009790741085
    Language: English
    Publisher: Journal of Marine Research/Yale
    Publication Date: 2009
    detail.hit.zdb_id: 410655-6
    detail.hit.zdb_id: 2066603-2
    SSG: 12
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  • 8
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    The Coastal Bottom Boundary Layer: A Note on the Model of Chapman and Lentz
    American Meteorological Society ; 2007
    In:  Journal of Physical Oceanography Vol. 37, No. 11 ( 2007-11-01), p. 2776-2784
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 37, No. 11 ( 2007-11-01), p. 2776-2784
    Abstract: The bottom boundary layer of a stratified flow on a coastal continental shelf is examined using the model of Chapman and Lentz. The flow is driven by a surface stress, uniform in the alongshore coordinate, in a downwelling-favorable direction. The stress diminishes in the offshore direction and produces an Ekman pumping, as well as an onshore Ekman flux. The model yields an interior flow, sandwiched between an upper Ekman layer and a bottom boundary layer. The interior has a horizontal density gradient produced by a balance between horizontal diffusion of density and vertical advection of a background vertical density gradient. The interior flow is vertically sheared and in thermal wind balance. Whereas the original model of Chapman and Lentz considered an alongshore flow that is freely evolving, the present note focuses on the equilibrium structure of a flow driven by stress and discusses the vertical and lateral structure of the flow and, in particular, the boundary layer thickness. The vertical diffusivity of density in the bottom boundary layer is considered so strong, locally, as to render the bottom boundary layer’s density a function of only offshore position. Boundary layer budgets of mass, momentum, and buoyancy determine the barotropic component of the interior flow as well as the boundary layer thickness, which is a function of the offshore coordinate. The alongshore flow has enhanced vertical shear in the boundary layer that reduces the alongshore flow in the boundary layer; however, the velocity at the bottom is generally not zero but produces a stress that locally balances the applied surface stress. The offshore transport in the bottom boundary layer therefore balances the onshore surface Ekman flux. The model predicts the thickness of the bottom boundary layer, which is a complicated function of several parameters, including the strength of the forcing stress, the vertical and horizontal diffusion coefficients in the interior, and the horizontal diffusion in the boundary layer. The model yields a boundary layer over only a finite portion of the bottom slope if the interior diffusion coefficients are too large; otherwise, the layer extends over the full lateral extent of the domain.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2007JPO3710.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 9
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    Eddy Formation near the West Coast of Greenland
    American Meteorological Society ; 2008
    In:  Journal of Physical Oceanography Vol. 38, No. 9 ( 2008-09-01), p. 1992-2002
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 38, No. 9 ( 2008-09-01), p. 1992-2002
    Abstract: This paper extends A. Bracco and J. Pedlosky’s investigation of the eddy-formation mechanism in the eastern Labrador Sea by including a more realistic depiction of the boundary current. The quasigeostrophic model consists of a meridional, coastally trapped current with three vertical layers. The current configuration and topographic domain are chosen to match, as closely as possible, the observations of the boundary current and the varying topographic slope along the West Greenland coast. The role played by the bottom-intensified component of the boundary current on the formation of the Labrador Sea Irminger Rings is explored. Consistent with the earlier study, a short, localized bottom-trapped wave is responsible for most of the perturbation energy growth. However, for the instability to occur in the three-layer model, the deepest component of the boundary current must be sufficiently strong, highlighting the importance of the near-bottom flow. The model is able to reproduce important features of the observed vortices in the eastern Labrador Sea, including the polarity, radius, rate of formation, and vertical structure. At the time of formation, the eddies have a surface signature as well as a strong circulation at depth, possibly allowing for the transport of both surface and near-bottom water from the boundary current into the interior basin. This work also supports the idea that changes in the current structure could be responsible for the observed interannual variability in the number of Irminger Rings formed.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2008JPO3669.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 10
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    Radiating Instability of a Meridional Boundary Current
    American Meteorological Society ; 2008
    In:  Journal of Physical Oceanography Vol. 38, No. 10 ( 2008-10-01), p. 2294-2307
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 38, No. 10 ( 2008-10-01), p. 2294-2307
    Abstract: A linear stability analysis of a meridional boundary current on the beta plane is presented. The boundary current is idealized as a constant-speed meridional jet adjacent to a semi-infinite motionless far field. The far-field region can be situated either on the eastern or the western side of the jet, representing a western or an eastern boundary current, respectively. It is found that when unstable, the meridional boundary current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field. This is the so-called radiating instability and is found in both barotropic and two-layer baroclinic configurations. A second but important conclusion concerns the differences in the stability properties of eastern and western boundary currents. An eastern boundary current supports a greater number of radiating modes over a wider range of meridional wavenumbers. It generates waves with amplitude envelopes that decay slowly with distance from the current. The radiating waves tend to have an asymmetrical horizontal structure—they are much longer in the zonal direction than in the meridional, a consequence of which is that unstable eastern boundary currents, unlike western boundary currents, have the potential to act as a source of zonal jets for the interior of the ocean.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2008JPO3853.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2008
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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