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  • 1
    In: Progress in Oceanography, Elsevier BV, Vol. 212 ( 2023-03), p. 102955-
    Type of Medium: Online Resource
    ISSN: 0079-6611
    RVK:
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2023
    detail.hit.zdb_id: 1497436-8
    detail.hit.zdb_id: 4062-9
    SSG: 21,3
    SSG: 14
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  • 2
    Online Resource
    Online Resource
    Cambridge University Press (CUP) ; 2019
    In:  Journal of Fluid Mechanics Vol. 871 ( 2019-07-25), p. 755-774
    In: Journal of Fluid Mechanics, Cambridge University Press (CUP), Vol. 871 ( 2019-07-25), p. 755-774
    Abstract: Inverting an evolving diffusive scalar field to reconstruct the underlying velocity field is an underdetermined problem. Here we show, however, that for two-dimensional incompressible flows, this inverse problem can still be uniquely solved if high-resolution tracer measurements, as well as velocity measurements along a curve transverse to the instantaneous scalar contours, are available. Such measurements enable solving a system of partial differential equations for the velocity components by the method of characteristics. If the value of the scalar diffusivity is known, then knowledge of just one velocity component along a transverse initial curve is sufficient. These conclusions extend to the shallow-water equations and to flows with spatially dependent diffusivity. We illustrate our results on velocity reconstruction from tracer fields for planar Navier–Stokes flows and for a barotropic ocean circulation model. We also discuss the use of the proposed velocity reconstruction in oceanographic applications to extend localized velocity measurements to larger spatial domains with the help of remotely sensed scalar fields.
    Type of Medium: Online Resource
    ISSN: 0022-1120 , 1469-7645
    Language: English
    Publisher: Cambridge University Press (CUP)
    Publication Date: 2019
    detail.hit.zdb_id: 1472346-3
    detail.hit.zdb_id: 218334-1
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  • 3
    Online Resource
    Online Resource
    American Meteorological Society ; 2017
    In:  Journal of Physical Oceanography Vol. 47, No. 2 ( 2017-02), p. 339-351
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 47, No. 2 ( 2017-02), p. 339-351
    Abstract: A novel multi-iteration statistical method for studying tracer spreading using drifter data is introduced. The approach allows for the best use of the available drifter data by making use of a simple iterative procedure, which results in the statistically probable map showing the likelihood that a tracer released at some source location would visit different geographical regions, along with the associated arrival travel times. The technique is tested using real drifter data in the North Atlantic. Two examples are considered corresponding to sources in the western and eastern North Atlantic Ocean, that is, Massachusetts Bay–like and Irish Sea–like sources, respectively. In both examples, the method worked well in estimating the statistics of the tracer transport pathways and travel times throughout the entire North Atlantic. The role of eddies versus mean flow is quantified using the same technique, and eddies are shown to significantly broaden the spread of a tracer. The sensitivity of the results to the size of the source domain is investigated and causes for this sensitivity are discussed.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2017
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 4
    Online Resource
    Online Resource
    American Meteorological Society ; 2020
    In:  Journal of Physical Oceanography Vol. 50, No. 7 ( 2020-07-01), p. 1839-1852
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 50, No. 7 ( 2020-07-01), p. 1839-1852
    Abstract: The Lagrangian characteristics of the surface flow field arising when an idealized, anticyclonic, mesoscale, isolated deep-ocean eddy collides with continental slope and shelf topography are explored. In addition to fluid parcel trajectories, we consider the trajectories of biological organisms that are able to navigate and swim, and for which shallow water is a destination. Of particular interest is the movement of organisms initially located in the offshore eddy, the manner in which the eddy influences the ability of the organisms to reach the shelf break, and the spatial and temporal distributions of organisms that do so. For nonswimmers or very slow swimmers, the organisms arrive at the shelf break in distinct pulses, with different pulses occurring at different locations along the shelf break. This phenomenon is closely related to the episodic formation of trailing vortices that are formed after the eddy collides with the continental slope, turns, and travels parallel to the coast. Analysis based on finite-time Lyapunov exponents reveals initial locations of all successful trajectories reaching the shoreline, and provides maps of the transport pathways showing that much of the cross-shelf-break transport occurs in the lee of the eddy as it moves parallel to the shore. The same analysis shows that the onshore transport is interrupted after a trailing vortex detaches. As the swimming speeds are increased, the organisms are influenced less by the eddy and tend to show up en mass and in a single pulse.
    Type of Medium: Online Resource
    ISSN: 0022-3670 , 1520-0485
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2020
    detail.hit.zdb_id: 2042184-9
    detail.hit.zdb_id: 184162-2
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  • 5
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2010
    In:  The Journal of the Acoustical Society of America Vol. 128, No. 4_Supplement ( 2010-10-01), p. 2387-2387
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 128, No. 4_Supplement ( 2010-10-01), p. 2387-2387
    Abstract: Many mid-latitude deep ocean environments are characterized by strongly range-dependent sound speed structure associated with mesoscale variability, including internal tides. Often much of this variability is describable as a combination of barotropic and lowest baroclinic mode variability. There are reasons to anticipate that ocean structure of this type leads only to a relatively benign range-dependent modulation of underwater sound fields. These ideas will be explained and tested using ECCO2 state estimates in the Philippine Sea. [Work supported by the ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2010
    detail.hit.zdb_id: 1461063-2
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  • 6
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2007
    In:  The Journal of the Acoustical Society of America Vol. 122, No. 3 ( 2007-09-01), p. 1440-1448
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 122, No. 3 ( 2007-09-01), p. 1440-1448
    Abstract: Consistent with earlier work by Kravtsov and Orlov, a simple general expression for the width of a Fresnel zone δrF in a smooth inhomogeneous environment is derived; this is the diffractive contribution to the width of a ray. In a stratified environment at long range, the general Fresnel zone width expression is shown to reduce approximately to one that is proportional to ∣α∣r(R−r)∕σ where α is the ray stability parameter, σ is the acoustic frequency, r is the range from the source to the field point of interest, and R is the source to receiver range. In a stratified environment on which a weak small-scale perturbation is superimposed, deterministic rays in the background environment that connect fixed end points break up into bundles of micromultipaths at moderate to long range and a second, scattering-induced, contribution δrs to the width of a ray must be considered. It is shown that δrs is proportional to ∣α∣r(R−r) and argued that in a micromultipathing environment the total effective width of a background ray is δrtot=δrF2+δrs2. Theoretical predictions are shown to agree well with travel-time sensitivity kernel calculations.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2007
    detail.hit.zdb_id: 1461063-2
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  • 7
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2009
    In:  The Journal of the Acoustical Society of America Vol. 126, No. 4_Supplement ( 2009-10-01), p. 2158-2158
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 126, No. 4_Supplement ( 2009-10-01), p. 2158-2158
    Abstract: Although ray methods have limitations, they remain extremely important because they provide insight into the underlying wave propagation physics that is difficult, if not impossible, to obtain by any other means. In this talk the utility of ray methods in long-range deep ocean sound propagation will be discussed and illustrated. Topics to be discussed include ray-mode duality and action quantization; adiabatic invariance for rays and modes; beamforming and Radon transforms; caustics and catastrophes; travel time sensitivity kernels, Fresnel zones and other measures of ray widths; nonlinear resonances, KAM theory, and mode coupling; the waveguide invariant and its ray equivalent; and beam dynamics—from weakly divergent to explosive. [Work supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2009
    detail.hit.zdb_id: 1461063-2
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  • 8
    Online Resource
    Online Resource
    Acoustical Society of America (ASA) ; 2004
    In:  The Journal of the Acoustical Society of America Vol. 116, No. 4_Supplement ( 2004-10-01), p. 2635-2635
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 116, No. 4_Supplement ( 2004-10-01), p. 2635-2635
    Abstract: In a range-independent environment with a single sound speed minimum, a transformation of the environment is available which guarantees that solutions of the standard parabolic wave equation in the transformed environment are asymptotically equivalent to solutions of the Helmholtz equation. In this paper an approximate transformation, to be used in conjunction with the Thomson–Chapman parabolic approximation, is described. Advantages of the approximate transformation over the exact transformation are its simplicity and the fact that it can be used in environments with multiple sound speed minima. Travel time errors, relative to the corresponding Helmholtz equation rays, associated with this approximation in typical deep ocean environments grow approximately linearly in range at a rate of approximately 0.1 ms/Mm. [Work supported by ONR and NSF.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    RVK:
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2004
    detail.hit.zdb_id: 1461063-2
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  • 9
    In: Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 109, No. 16 ( 2012-04-17), p. 5984-5988
    Abstract: The Tōhoku earthquake and tsunami of March 11, 2011, resulted in unprecedented radioactivity releases from the Fukushima Dai-ichi nuclear power plants to the Northwest Pacific Ocean. Results are presented here from an international study of radionuclide contaminants in surface and subsurface waters, as well as in zooplankton and fish, off Japan in June 2011. A major finding is detection of Fukushima-derived 134 Cs and 137 Cs throughout waters 30–600 km offshore, with the highest activities associated with near-shore eddies and the Kuroshio Current acting as a southern boundary for transport. Fukushima-derived Cs isotopes were also detected in zooplankton and mesopelagic fish, and unique to this study we also find 110m Ag in zooplankton. Vertical profiles are used to calculate a total inventory of ∼2 PBq 137 Cs in an ocean area of 150,000 km 2 . Our results can only be understood in the context of our drifter data and an oceanographic model that shows rapid advection of contaminants further out in the Pacific. Importantly, our data are consistent with higher estimates of the magnitude of Fukushima fallout and direct releases [Stohl et al. (2011) Atmos Chem Phys Discuss 11:28319–28394; Bailly du Bois et al. (2011) J Environ Radioact , 10.1016/j.jenvrad.2011.11.015]. We address risks to public health and marine biota by showing that though Cs isotopes are elevated 10–1,000× over prior levels in waters off Japan, radiation risks due to these radionuclides are below those generally considered harmful to marine animals and human consumers, and even below those from naturally occurring radionuclides.
    Type of Medium: Online Resource
    ISSN: 0027-8424 , 1091-6490
    RVK:
    RVK:
    Language: English
    Publisher: Proceedings of the National Academy of Sciences
    Publication Date: 2012
    detail.hit.zdb_id: 209104-5
    detail.hit.zdb_id: 1461794-8
    SSG: 11
    SSG: 12
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  • 10
    Online Resource
    Online Resource
    AIP Publishing ; 2010
    In:  Chaos: An Interdisciplinary Journal of Nonlinear Science Vol. 20, No. 1 ( 2010-03-01)
    In: Chaos: An Interdisciplinary Journal of Nonlinear Science, AIP Publishing, Vol. 20, No. 1 ( 2010-03-01)
    Abstract: The term “Lagrangian coherent structure” (LCS) is normally used to describe numerically detected structures whose properties are similar to those of stable and unstable manifolds of hyperbolic trajectories. The latter structures are invariant curves, i.e., material curves of fluid that serve as transport barriers. In this paper we use the term LCS to describe a different type of structure whose properties are similar to those of invariant tori in certain classes of two-dimensional incompressible flows. Like stable and unstable manifolds, invariant tori are invariant curves that serve as transport barriers. There are many differences, however, between traditional LCSs and invariant-tori-like LCSs. These differences are discussed with an emphasis on numerical techniques that can be used to identify invariant-tori-like LCSs. Structures of this type are often present in geophysical flows where zonal jets are present. A prime example of an invariant-torus-like LCS is the transport barrier near the core of the polar night jet in the Earth’s lower and middle stratospheres in the austral winter and early spring; this is the barrier that traps ozone-depleted air inside the ozone hole. This example is investigated using both a simple analytically prescribed flow and a velocity field produced by a general circulation model of the Earth’s atmosphere.
    Type of Medium: Online Resource
    ISSN: 1054-1500 , 1089-7682
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 1472677-4
    SSG: 11
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