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  • 1
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    Propagation of North Atlantic Deep Water anomalies (2018)
    American Meteorological Society
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Meteorological Society, 2018. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 48 (2018): 1831-1848, doi:10.1175/JPO-D-18-0068.1.
    Description: We present a simplified theory using reduced-gravity equations for North Atlantic Deep Water (NADW) and its variation driven by high-latitude deep-water formation. The theory approximates layer thickness on the eastern boundary with domain-averaged layer thickness and, in tandem with a mass conservation argument, retains fundamental physics for cross-equatorial flows on interannual and longer forcing time scales. Layer thickness anomalies are driven by a time-dependent northern boundary condition that imposes a southward volume flux representative of a variable source of NADW and damped by diapycnal mixing throughout the basin. Moreover, an outflowing southern boundary condition imposes a southward volume flux that generally differs from the volume flux at the northern boundary, giving rise to temporal storage of NADW within the Atlantic basin. Closed form analytic solutions for the amplitude and phase are provided when the variable source of NADW is sinusoidal. We provide a nondimensional analysis that demonstrates that solution behavior is primarily controlled by two parameters that characterize the meridional extent of the southern basin and the width of the basin relative to the equatorial deformation radius. Similar scaling applied to the time-lagged equations of Johnson and Marshall provides a clear connection to their results. Numerical simulations of reduced-gravity equations agree with analytic predictions in linear, turbulent, and diabatic regimes. The theory introduces a simple analytic framework for studying idealized buoyancy- and wind-driven cross-equatorial flows on interannual and longer time scales.
    Description: This research was supported by the National Science Foundation under Grant OCE- 1634468.
    Description: 2019-02-15
    Keywords: North Atlantic Ocean ; Tropics ; Meridional overturning circulation ; Ocean circulation ; Shallow-water equations
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Wind-forced variability of the remote meridional overturning circulation (2020)
    American Meteorological Society
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(2), (2020): 455-469, doi:10.1175/JPO-D-19-0190.1.
    Description: The mechanisms by which time-dependent wind stress anomalies at midlatitudes can force variability in the meridional overturning circulation at low latitudes are explored. It is shown that winds are effective at forcing remote variability in the overturning circulation when forcing periods are near the midlatitude baroclinic Rossby wave basin-crossing time. Remote overturning is required by an imbalance in the midlatitude mass storage and release resulting from the dependence of the Rossby wave phase speed on latitude. A heuristic theory is developed that predicts the strength and frequency dependence of the remote overturning well when compared to a two-layer numerical model. The theory indicates that the variable overturning strength, relative to the anomalous Ekman transport, depends primarily on the ratio of the meridional spatial scale of the anomalous wind stress curl to its latitude. For strongly forced systems, a mean deep western boundary current can also significantly enhance the overturning variability at all latitudes. For sufficiently large thermocline displacements, the deep western boundary current alternates between interior and near-boundary pathways in response to fluctuations in the wind, leading to large anomalies in the volume of North Atlantic Deep Water stored at midlatitudes and in the downstream deep western boundary current transport.
    Description: MAS and DN were supported by the National Science Foundation under Grant OCE-1634468.
    Description: 2020-11-10
    Keywords: Meridional overturning circulation ; Ocean circulation ; Rossby waves ; Thermocline circulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Propagation of North Atlantic Deep Water Anomalies (2018)
    American Meteorological Society
    Details
    Publication Date: 2018-08-01
    Description: We present a simplified theory using reduced-gravity equations for North Atlantic Deep Water (NADW) and its variation driven by high-latitude deep-water formation. The theory approximates layer thickness on the eastern boundary with domain-averaged layer thickness and, in tandem with a mass conservation argument, retains fundamental physics for cross-equatorial flows on interannual and longer forcing time scales. Layer thickness anomalies are driven by a time-dependent northern boundary condition that imposes a southward volume flux representative of a variable source of NADW and damped by diapycnal mixing throughout the basin. Moreover, an outflowing southern boundary condition imposes a southward volume flux that generally differs from the volume flux at the northern boundary, giving rise to temporal storage of NADW within the Atlantic basin. Closed form analytic solutions for the amplitude and phase are provided when the variable source of NADW is sinusoidal. We provide a nondimensional analysis that demonstrates that solution behavior is primarily controlled by two parameters that characterize the meridional extent of the southern basin and the width of the basin relative to the equatorial deformation radius. Similar scaling applied to the time-lagged equations of Johnson and Marshall provides a clear connection to their results. Numerical simulations of reduced-gravity equations agree with analytic predictions in linear, turbulent, and diabatic regimes. The theory introduces a simple analytic framework for studying idealized buoyancy- and wind-driven cross-equatorial flows on interannual and longer time scales.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 4
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    Statistical classification of flow morphology in rapidly rotating Rayleigh-Bénard convection (2014)
    American Institute of Physics
    Details
    Publication Date: 2014-08-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 5
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    Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers (2016)
    American Physical Society
    Details
    Publication Date: 2016-12-08
    Electronic ISSN: 2469-990X
    Topics: Physics
    Published by American Physical Society
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  • 6
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    Nanoparticle-based monitoring of cell therapy (2011)
    Institute of Physics
    Details
    Publication Date: 2011-11-21
    Print ISSN: 0957-4484
    Electronic ISSN: 1361-6528
    Topics: Physics
    Published by Institute of Physics
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  • 7
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    Wind-Forced Variability of the Remote Meridional Overturning Circulation (2020)
    American Meteorological Society
    Details
    Publication Date: 2020-02-01
    Description: The mechanisms by which time-dependent wind stress anomalies at midlatitudes can force variability in the meridional overturning circulation at low latitudes are explored. It is shown that winds are effective at forcing remote variability in the overturning circulation when forcing periods are near the midlatitude baroclinic Rossby wave basin-crossing time. Remote overturning is required by an imbalance in the midlatitude mass storage and release resulting from the dependence of the Rossby wave phase speed on latitude. A heuristic theory is developed that predicts the strength and frequency dependence of the remote overturning well when compared to a two-layer numerical model. The theory indicates that the variable overturning strength, relative to the anomalous Ekman transport, depends primarily on the ratio of the meridional spatial scale of the anomalous wind stress curl to its latitude. For strongly forced systems, a mean deep western boundary current can also significantly enhance the overturning variability at all latitudes. For sufficiently large thermocline displacements, the deep western boundary current alternates between interior and near-boundary pathways in response to fluctuations in the wind, leading to large anomalies in the volume of North Atlantic Deep Water stored at midlatitudes and in the downstream deep western boundary current transport.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 8
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    The asymptotic equivalence of fixed heat flux and fixed temperature thermal boundary conditions for rapidly rotating convection (2015)
    Cambridge University Press
    Details
    Publication Date: 2015-11-04
    Description: The influence of fixed temperature and fixed heat flux thermal boundary conditions on rapidly rotating convection in the plane layer geometry is investigated for the case of stress-free mechanical boundary conditions. It is shown that whereas the leading-order system satisfies fixed temperature boundary conditions implicitly, a double boundary layer structure is necessary to satisfy the fixed heat flux thermal boundary conditions. The boundary layers consist of a classical Ekman layer adjacent to the solid boundaries that adjust viscous stresses to zero, and a layer in thermal wind balance just outside the Ekman layers that adjusts the normal derivative of the temperature fluctuation to zero. The influence of these boundary layers on the interior geostrophically balanced convection is shown to be asymptotically weak, however. Upon defining a simple rescaling of the thermal variables, the leading-order reduced system of governing equations is therefore equivalent for both boundary conditions. These results imply that any horizontal thermal variation along the boundaries that varies on the scale of the convection has no leading-order influence on the interior convection, thus providing insight into geophysical and astrophysical flows where stress-free mechanical boundary conditions are often assumed. © 2015 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 9
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    Investigations of non-hydrostatic, stably stratified and rapidly rotating flows (2016)
    Cambridge University Press
    Details
    Publication Date: 2016-07-25
    Description: We present an investigation of rapidly rotating (small Rossby number R0〈〈1) stratified turbulence where the stratification strength is varied from weak (large Froude number Fr〉〉1) to strong (Fr〈〈1). The investigation is set in the context of a reduced model derived from the Boussinesq equations that retains anisotropic inertia-gravity waves with order-one frequencies and highlights a regime of wave-eddy interactions. Numerical simulations of the reduced model are performed where energy is injected by a stochastic forcing of vertical velocity, which forces wave modes only. The simulations reveal two regimes: characterized by the presence of well-formed, persistent and thin turbulent layers of locally weakened stratification at small Froude numbers, and by the absence of layers at large Froude numbers. Both regimes are characterized by a large-scale barotropic dipole enclosed by small-scale turbulence. When the Reynolds number is not too large, a direct cascade of barotropic kinetic energy is observed, leading to total energy equilibration. We examine net energy exchanges that occur through vortex stretching and vertical buoyancy flux and diagnose the horizontal scales active in these exchanges. We find that the baroclinic motions inject energy directly to the largest scales of the barotropic mode, implying that the large-scale barotropic dipole is not the end result of an inverse cascade within the barotropic mode. © 2016 Cambridge University Press.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Cambridge University Press
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  • 10
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    Tracking Mesenchymal Stem Cells with Iron Oxide Nanoparticle Loaded Poly(lactide-co-glycolide) Microparticles (2012)
    American Chemical Society
    Details
    Publication Date: 2012-07-12
    Print ISSN: 1530-6984
    Electronic ISSN: 1530-6992
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society
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