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  • 1
    Online Resource
    Online Resource
    Potential and Limitations of a Commercial Broadband Echo Sounder for Remote Observations of Turbulent Mixing
    American Meteorological Society ; 2022
    In:  Journal of Atmospheric and Oceanic Technology Vol. 39, No. 12 ( 2022-12), p. 1985-2003
    Details
    In: Journal of Atmospheric and Oceanic Technology, American Meteorological Society, Vol. 39, No. 12 ( 2022-12), p. 1985-2003
    Abstract: Stratified oceanic turbulence is strongly intermittent in time and space, and therefore generally underresolved by currently available in situ observational approaches. A promising tool to at least partly overcome this constraint are broadband acoustic observations of turbulent microstructure that have the potential to provide mixing parameters at orders of magnitude higher resolution compared to conventional approaches. Here, we discuss the applicability, limitations, and measurement uncertainties of this approach for some prototypical turbulent flows (stratified shear layers, turbulent flow across a sill), based on a comparison of broadband acoustic observations and data from a free-falling turbulence microstructure profiler. We find that broadband acoustics are able to provide a quantitative description of turbulence energy dissipation in stratified shear layers (correlation coefficient r = 0.84) if the stratification parameters required by the method are carefully preprocessed. Essential components of our suggested preprocessing algorithm are 1) a vertical low-pass filtering of temperature and salinity profiles at a scale slightly larger than the Ozmidov length scale of turbulence and 2) an automated elimination of weakly stratified layers according to a gradient threshold criterion. We also show that in weakly stratified conditions, the acoustic approach may yield acceptable results if representative averaged vertical temperature and salinity gradients rather than local gradients are used. Our findings provide a step toward routine turbulence measurements in the upper ocean from moving vessels by combining broadband acoustics with in situ CTD profiles.
    Type of Medium: Online Resource
    ISSN: 0739-0572 , 1520-0426
    URL: Article
    URL: Article
    DOI: 10.1175/JTECH-D-21-0169.1
    DOI: 10.1175/JTECH-D-21-0169.s1
    Language: Unknown
    Publisher: American Meteorological Society
    Publication Date: 2022
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  • 2
    Online Resource
    Online Resource
    Gravity Current Dynamics and Entrainment—A Process Study Based on Observations in the Arkona Basin
    American Meteorological Society ; 2007
    In:  Journal of Physical Oceanography Vol. 37, No. 8 ( 2007-08-01), p. 2094-2113
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 37, No. 8 ( 2007-08-01), p. 2094-2113
    Abstract: A 19-h time series of dissipation, stratification, and horizontal velocities has been obtained for a dense gravity current flowing into the Arkona Basin in the western Baltic Sea. The observations are compared with one-dimensional, quasi-steady theory, in which the gravity component in the flow direction is balanced by bottom friction, while that in the cross-flow direction is balanced by the Coriolis force. The observations deviate from the theory in that the bottom shear stress is more than 2 times as large as that required to balance the gravity. Several reasons for this discrepancy are discussed. A 1D turbulence model is also compared with the observations. Profiles of velocity, stratification, and dissipation rates generally show similar variations with depth as the observations, although the observed dissipation rates are somewhat larger than the modeled and the modeled transverse velocities are much larger than the observed. Subsequently, the model is used to investigate the variation of the entrainment parameter for a large range of Ekman and Froude numbers. Within the modeled parameter space, the entrainment parameter can be collapsed onto a curve that is an increasing function of both the Froude and the Ekman numbers. There is one puzzling result of the observations that differs from the model results and earlier observations: the observed entrainment rate increases dramatically during the observation period, where the Froude number decreases slightly. Some reasons for this increase are discussed.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/JPO3110.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2007
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  • 3
    Online Resource
    Online Resource
    Dynamics of Rotating Shallow Gravity Currents Passing through a Channel. Part II: Analysis
    American Meteorological Society ; 2009
    In:  Journal of Physical Oceanography Vol. 39, No. 10 ( 2009-10-01), p. 2402-2416
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 39, No. 10 ( 2009-10-01), p. 2402-2416
    Abstract: The physics of frictional control for channelized rotating gravity currents are analyzed using an extensive dataset including hydrographic, current, and microstructure measurements from the western Baltic Sea. Rotational effects in these gravity currents, characterized by Ekman numbers of the order of one and subcritical Froude numbers, induce a complex transverse circulation that strongly affects the internal dynamics. The key component of this circulation is a geostrophically balanced transverse jet in the interface that modifies the entrainment process by (i) laterally draining the interface and (ii) providing additional interfacial shear comparable to the down-channel shear. The recirculation of mixed interfacial fluid into the interior distorts the internal density structure of the gravity current, and creates a thermal wind shear in the interior that is comparable to the observed shear. Using a theoretical model, this effect is shown to be responsible for the three-layer structure of the transverse velocity with the near-bottom velocity and stress directed opposite to the Ekman transport. The analysis confirms the key assumption in available models for frictional control in rotating gravity currents: the transverse Ekman transport is balanced by the geostrophic transport due to the down-channel tilt of the interface.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2009JPO4164.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
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  • 4
    Online Resource
    Online Resource
    Entrainment in Shallow Rotating Gravity Currents: A Modeling Study
    American Meteorological Society ; 2010
    In:  Journal of Physical Oceanography Vol. 40, No. 8 ( 2010-08-01), p. 1819-1834
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 40, No. 8 ( 2010-08-01), p. 1819-1834
    Abstract: The physics of shallow gravity currents passing through a rotating channel at subcritical Froude number is investigated here with a series of idealized numerical experiments. It is found that the combined effects of friction and rotation set up a complex transverse circulation that has some crucial implications for the entrainment process. A key component of this secondary circulation is a geostrophically balanced transverse jet in the interface that laterally drains fluid from the interface. This effect is shown to result in a strong cross-channel asymmetry and a spatial separation of the entrainment process: drained interfacial fluid is partly replaced by entrained ambient fluid on the deep side of the gravity current, whereas the downward mixing of buoyant fluid occurs on the shallow side. These results, closely corresponding to recent measurements in a shallow, channelized gravity current in the western Baltic Sea, illustrate that the description of entrainment as a strictly vertical mixing process with the help of local bulk parameters like the Froude number is not generally applicable in rotating gravity currents.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2010JPO4367.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2010
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  • 5
    Online Resource
    Online Resource
    Dynamics of medium-intensity dense water plumes in the Arkona Basin, Western Baltic Sea
    Springer Science and Business Media LLC ; 2005
    In:  Ocean Dynamics Vol. 55, No. 5-6 ( 2005-12), p. 391-402
    Details
    In: Ocean Dynamics, Springer Science and Business Media LLC, Vol. 55, No. 5-6 ( 2005-12), p. 391-402
    Type of Medium: Online Resource
    ISSN: 1616-7341 , 1616-7228
    URL: Article
    DOI: 10.1007/s10236-005-0025-2
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2005
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    SSG: 14
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  • 6
    Online Resource
    Online Resource
    Direct observations of a medium-intensity inflow into the Baltic Sea
    Elsevier BV ; 2006
    In:  Continental Shelf Research Vol. 26, No. 19 ( 2006-12), p. 2393-2414
    Details
    In: Continental Shelf Research, Elsevier BV, Vol. 26, No. 19 ( 2006-12), p. 2393-2414
    Type of Medium: Online Resource
    ISSN: 0278-4343
    URL: Article
    DOI: 10.1016/j.csr.2006.07.004
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2006
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    SSG: 14
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  • 7
    Online Resource
    Online Resource
    Dynamics of Rotating Shallow Gravity Currents Passing through a Channel. Part I: Observation of Transverse Structure
    American Meteorological Society ; 2009
    In:  Journal of Physical Oceanography Vol. 39, No. 10 ( 2009-10-01), p. 2385-2401
    Details
    In: Journal of Physical Oceanography, American Meteorological Society, Vol. 39, No. 10 ( 2009-10-01), p. 2385-2401
    Abstract: A detailed dataset describing a quasi-stationary bottom gravity current, approximately 10 m thick and 10 km wide, passing through a channel-like constriction in the western Baltic Sea is presented. The data include full-depth, synoptic, and highly resolved transects of stratification and turbulence parameters, as well as detailed velocity transects across the gravity current at different down-channel locations. The velocity data reveal a persistent transverse circulation, creating a characteristic wedge-shaped density structure in the interface. A strong asymmetry was also found in the interior of the gravity current, where the evolution of a dynamically significant transverse density gradient to the right of the down-channel flow was observed. Spectral analysis of the near-bottom velocities showed a surprisingly strong contribution to the bottom stress from low-frequency motions with periods up to 30 min that are possibly related to internal wave effects. Cross-channel transects of shear microstructure were used to investigate the transverse variation of local entrainment rates and bottom stresses. These data indicate that frictional control is essential for this class of gravity currents that are characterized by subcritical Froude numbers, small entrainment, strong rotational effects, and small thickness compared to the bottom Ekman layer.
    Type of Medium: Online Resource
    ISSN: 1520-0485 , 0022-3670
    URL: Article
    DOI: 10.1175/2009JPO4159.1
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
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  • 8
    Online Resource
    Online Resource
    Reply to: "Comments on 'A generic length-scale equation for geophysical turbulence models'" by L. Kantha and S. Carniel
    Journal of Marine Research/Yale ; 2003
    In:  Journal of Marine Research Vol. 61, No. 5 ( 2003-09-01), p. 703-706
    Details
    In: Journal of Marine Research, Journal of Marine Research/Yale, Vol. 61, No. 5 ( 2003-09-01), p. 703-706
    Type of Medium: Online Resource
    ISSN: 0022-2402 , 1543-9542
    URL: Article
    DOI: 10.1357/002224003771816016
    Language: English
    Publisher: Journal of Marine Research/Yale
    Publication Date: 2003
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    SSG: 12
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  • 9
    Online Resource
    Online Resource
    The Baltic Sea Tracer Release Experiment: 1. Mixing rates
    American Geophysical Union (AGU) ; 2012
    In:  Journal of Geophysical Research: Oceans Vol. 117, No. C1 ( 2012-01)
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 117, No. C1 ( 2012-01)
    Abstract: Mixing rates in the Gotland Basin are dominated by boundary mixing processes The time scale for Gotland Basin deep water renewal is approximately 2 years Mixing rates determined from the tracer CF3SF5
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2011JC007439
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2012
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    SSG: 16,13
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  • 10
    Online Resource
    Online Resource
    Observations and numerical modelling of mixed-layer turbulence: Do they represent the same statistical quantities?
    Elsevier BV ; 2005
    In:  Deep Sea Research Part II: Topical Studies in Oceanography Vol. 52, No. 9-10 ( 2005-05), p. 1069-1074
    Details
    In: Deep Sea Research Part II: Topical Studies in Oceanography, Elsevier BV, Vol. 52, No. 9-10 ( 2005-05), p. 1069-1074
    Type of Medium: Online Resource
    ISSN: 0967-0645
    URL: Article
    DOI: 10.1016/j.dsr2.2005.03.002
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2005
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    SSG: 14
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