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  • 1
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    Turbulent momentum and salt transport in the mixing zone of the Elbe estuary (1989)
    Elsevier
    In:  Estuarine, Coastal and Shelf Science, 28 (6). pp. 615-638.
    Details
    Publication Date: 2017-01-04
    Description: Measurements in the mixing zone of the Elbe estuary were performed during three consecutive tidal cycles with three types of instruments—a moored tripod with velocity and temperature/conductivity/light attenuation sensors, a profiling sonde with similar sensors lowered from an anchored vessel, and instrumented moorings. Acoustic-travel-time sensors were used for velocity measurements. Spectral analysis of 12·8 min pieces of the obtained time series gives results that are consistent with isotropic turbulence for part of the frequency space. Temporal changes of turbulent kinetic energy are correlated with tidal current velocity. A retardation is found between changes in tidal current and turbulent energy. Not all shear stress terms are in similar phase with tidal flow. Mean gradients, Reynolds stress terms, and turbulent salt flux terms are combined to determine eddy viscosity and eddy diffusion coefficients.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/0272-7714(89)90050-4
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Drag Coefficients of Oceanographic Mooring Components (1986)
    AMS (American Meteorological Society)
    In:  Journal of Atmospheric and Oceanic Technology, 3 (2). pp. 255-264.
    Details
    Publication Date: 2020-08-04
    Description: The inclination of oceanographic mooring lines due to current drag causes errors in time series observations of currents and temperatures. The prediction of this effect requires knowledge of the drag coefficients for the mooring components. Drag coefficients, known for simple geometric shapes such as spheres or cylinders, are commonly used for mooring response computations. Selected mooring components (buoyancy elements and instruments) were tested in a tow tank to determine their actual drag coefficients. Over the Reynolds Number range, typical of oceanic conditions, deviations of the drag coefficient up to 50% are found when compared with the appropriate simple geometric shape coefficients. A set of model moorings and model current profiles is used to determine the resulting changes in component depth level and displacement. The changes in horizontal displacement of the upper part of the mooring are on the order of 10% in extreme cases and 1% under typical conditions. Their effects on current measurements will usually be negligible. However, the related vertical displacements are on the order 100 to 10 m. Such vertical displacements may carry instruments to depth levels where currents and particularly thermocline temperatures are sufficiently different from the intended level to cause errors in the time series observations.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0426(1986)003〈0255:DCOOMC〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Baroclinic Flow and Transient-Tracer Fields in the Canary–Cape Verde Basin (1986)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 16 (5). pp. 814-826.
    Details
    Publication Date: 2018-04-04
    Description: Simulated transient-tracer distributions (tritium, 3H3, freons) on the isopycnal horizons σ0=26.5 and 26.8 kg m−3 are presented for the East Atlantic, 10° −40°N. Tracer transport is modeled by employing a baroclinic flow field based on empirical data in a kinematic isopycnal advection-diffusion numerical model, in which winter convection is taken as the mechanism of communication with the ocean surface layer, and the isopycnal diffusivity is a free parameter. Diapucnic transport is ignored. The simulations employ time-dependent tracer boundary conditions, which are constructed on the basis of available observations. Simulations are compared to data obtained on a meridional section in 1981 (F/S Meteor, cruise 56/5). Best simulations were obtained by means of a subjective optimization procedure. On both levels, the observed distributions and the best simulated distributions agree well. The fact that the surface boundary conditions and interior distributions of the tracers are distinctly different leads us to the conclusion that our model provides a consistent description of upper main-thermocline ventilation and interior transport Surface-water densities in February are found to represent adequately the winter outcrop boundaries with an uncertainty of about ±300 km across. The required isopycnal diffusivity south of 29°N is 1700 m2 s−1, and 2900 m2 s−1 further north (+70/−40%). Interior transport is found to be predominantly advective. Advective ventilation across 30.5°N east of 33°W amounts to only 12% and 40% for the 26.5 and 26.8 horizons of the total ventilation rates reported by Sarmiento. The North Atlantic/South Atlantic Central Water boundary near 15°N is found to be predominantly determined by advection.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0485(1986)016〈0814:BFATTF〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    The Madeira Mode Water (1987)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 17 (10). pp. 1561-1570.
    Details
    Publication Date: 2020-08-04
    Description: Quasi-homogeneous layers in vertical profiles of temperature and salinity in the eastern North Atlantic near Madeira indicate the existence of a subtropical Mode Water in the Eastern Basin. Temperature sections show a maximum horizontal extent of at least 500 km. The frequency distribution analysis of homogeneous layers in a historical XBT dataset shows a Mode Water formation region near and to the north of Madeira. This Mode Water is found at increasing depths and displaced to the west and southwest during the course of the year after its formation by wintertime convection. It disappears almost completely, due to mixing, before the next winter. Volume estimates suggest that this Madeira Mode Water in the eastern Atlantic accounts for 15–20% of the total Central Water formation in the corresponding density range as obtained from tracer studies in the North Atlantic gyre.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0485(1987)017〈1561:TMMW〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Vertical coherence of short-periodic current variations (1971)
    Elsevier
    In:  Deep Sea Research and Oceanographic Abstracts, 18 (2). pp. 179-191.
    Details
    Publication Date: 2016-09-22
    Description: A study is described which attempts to obtain information about the vertical correlation of ocean currents at frequencies higher than inertial. Current velocity and temperature data for sensor separations of 4–12 m were taken with a mooring at ‘Site D’. The coherence and phase spectra for velocity component pairs reveals that motions are rotational at low frequencies. A cut-off frequency exists above which coherence drops to low values. The limiting frequency coincides with the minimum Väisälä frequency of the total water column. These cross-spectral properties support the assumption that the motion in this frequency range is governed by internal wave dynamics. The coherence and phase spectra of temperature pairs indicate that a field of temperature structure is superimposed on the mean field which is weakly correlated to the field of motion.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/0011-7471(71)90108-2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Observations of internal wave coherence in the deep ocean (1974)
    Elsevier
    In:  Deep Sea Research and Oceanographic Abstracts, 21 (8). pp. 597-610.
    Details
    Publication Date: 2016-09-22
    Description: An experiment is described which was aimed at testing assumptions and predictions of the internal wave model suggested by Garrett and Munk (1972). Two moorings were set at a depth of 2660 m with a horizontal separation of 920 m only. The results of current and temperature measurements on these moorings indicate that the field of motion is probably horizontally isotropic in the inertio-gravitational wave band. The limiting frequency for horizontal coherence is three times the frequency predicted by the theoretical model. The phase of the vertical coherence is stable over a wide frequency range and the coherence decreases towards higher frequencies. This may be due to coherent motion contaminated by uncorrelated noise at high frequencies. The results are basically in agreement with the theoretical model when taking a number of modes below 10.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/0011-7471(74)90045-X
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    The fine-structure contamination of vertical velocity spectra in the deep ocean (1974)
    Elsevier
    In:  Deep Sea Research and Oceanographic Abstracts, 21 (1). pp. 37-46.
    Details
    Publication Date: 2018-03-08
    Description: When determining vertical velocity spectra from temperature time series and the mean vertical temperature gradient, restrictions may arise friom the existence of fine-structre. Phillips (1971) and Garrett and Munk (1971_ have shown that the fine-structure contamination of internal gravity wave spectra can be written as a function of some statistical properties of the internal wave field and the vertical wave number spectrum of the fine-structure. A consistent set of current and temperature data was obtained during an experiment at Site D to study this problem. The wave number spectrum of the vertical temperature fine-structure and the apparent frequently spectrum of internal waves are determined from these data. In contrast to the asasumptions in the above models, our fine-structure data imply a wave number spectrum proportional to (wave number)−3 in the range which is important here. Using the above set of data, a model is suggested to describe the effect of fine-structure on vertical velocity spectra computed with the mean vertical temperature gradient. It indicates a maximum fine-structure contamination of the true frequency spectrum of internal gravity waves in the middle of the internal wave band, with less contamination at low and high frequencies.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/0011-7471(74)90017-5
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Strong Current Events Related to a Subtropical Front in the Northeast Atlantic (1985)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 15 (7). pp. 885-897.
    Details
    Publication Date: 2020-08-04
    Description: Long-term temperature and current-meter records from moorings in the northern Canary Basin display strong current events with time scales between one and three months and large vertical scales of several thousand meters. The data are compared to hydrographic surveys in the area that show a meandering subtropical front. The strong current events are found to be related to the passage of the front through the mooring positions. An analysis of composite time series, for selected depths, indicates cases of westward and of eastward propagation of frontal meanders. The frontal pattern is also found in geopotential anomalies inferred from historical XBT data sets, suggesting that the front is a persistent feature of the density field. In two cases strong current events appear to be related to a Mediterranean Water lens.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0485(1985)015〈0885:SCERTA〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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