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  • 1
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    Institut für Meereskunde Kiel
    In:  Institut für Meereskunde Kiel, Kiel, Germany, 16 pp.
    Publication Date: 2018-08-20
    Type: Report , NonPeerReviewed
    Format: text
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  • 2
    Publication Date: 2018-09-27
    Type: Dataset
    Format: text/tab-separated-values, 268637 data points
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  • 3
    Publication Date: 2018-09-27
    Type: Dataset
    Format: text/tab-separated-values, 86724 data points
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The ocean fluctuates on a wide range of spatial and temporal scales4. The measured potential-energy spectrum of the circulation is mostly 'red', that is, the energy density increases with increasing spatial and temporal scales, but with a marked peak at the annual cycle. However, the kinetic-energy ...
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  • 5
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    American Institute of Physics for the Acoustical Society of America
    In:  Journal of the Acoustical Society of America, 100 (2) . pp. 797-813.
    Publication Date: 2018-04-13
    Description: The recently introduced notion of peak arrivals [Athanassoulis and Skarsoulis, J. Acoust. Soc. Am. 97, 3575–3588 (1995)], defined as the significant local maxima of the arrival pattern, is studied here as a modeling basis for performing ocean tomography. Peak arrivals constitute direct theoretical counterparts of experimentally observed peaks, and offer a complete modeling of experimental observables, even in cases where ray or modal arrivals cannot be resolved. The coefficients of the resulting peak‐inversion system, relating travel‐time with sound‐speed perturbations, are explicitly calculated in the case of range‐independent environments using normal‐mode theory. To apply the peak‐inversion scheme to tomography the peak identification and tracking problem is examined from a statistical viewpoint; maximum‐likelihood and least‐square solutions are derived and discussed. The particular approach adopted treats the identification and tracking problem in close relation to the inversion procedure; all possibilities of associating observed peaks with background arrivals are examined via trial inversions, and the best peak identification is selected with respect to a least‐square criterion. The feasibility of peak tomography is subsequently demonstrated using first synthetic data and then measured data from the THETIS‐I experiment. In the synthetic case the performance of the overall scheme is found to be satisfactory both with noise‐free and noisy data. Furthermore, the identification, tracking, and inversion results using experimental acoustic data from THETIS‐I are in good agreement with independent field observations.
    Type: Article , PeerReviewed
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  • 6
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    IEEE
    In:  In: OCEANS '95. MTS/IEEE. Challenges of Our Changing Global Environment. Conference Proceedings. IEEE, San Diego, Calif., pp. 1631-1642.
    Publication Date: 2017-02-01
    Description: New off-the-shelf hardware has allowed improved techniques for acoustic transponder deployment and surveying, saving time and improving the accuracy of results. In particular, affordable acoustic deck units which allow continuous computer sampling of acoustic ranges while the ship is under way (merged with simultaneous GPS position data), allow application of a variety of survey techniques, to determine the exact transponder positions or separations. Apart from a particular hardware setup used, various possible analysis techniques are summarized and results compared from a number of applications. In addition, the positioning problem using 2 or 3 acoustic transponders is discussed. The solutions are presented together with their respective errors, allowing simple rule-of-thumb estimates for positioning (or velocity) accuracy, as a function of the uncertainty in input parameters (e.g. transponder positions, acoustic travel time, depth measurement).
    Type: Book chapter , NonPeerReviewed
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  • 7
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    In:  [Other] In: MFSTEP 2nd Annual Meeting, 08.02, Bologna, Italy .
    Publication Date: 2012-02-23
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 8
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    AGU / Wiley
    In:  Journal of Geophysical Research: Oceans, 102 (C6). pp. 12515-12537.
    Publication Date: 2018-04-30
    Description: The Theoretical and Experimental Tomography in the Sea Experiment (THETIS 1) took place in the Gulf of Lion to observe the evolution of the temperature field and the process of deep convection during the 1991–1992 winter. The temperature measurements consist of moored sensors, conductivity‐temperature‐depth and expendable bathythermograph surveys, and acoustic tomography. Because of this diverse data set and since the field evolves rather fast, the analysis uses a unified framework, based on estimation theory and implementing a Kaiman filter. The resolution and the errors associated with the model are systematically estimated. Temperature is a good tracer of water masses. The time‐evolving three‐dimensional view of the field resulting from the analysis shows the details of the three classical convection phases: preconditioning, vigourous convection, and relaxation. In all phases, there is strong spatial nonuniformity, with mesoscale activity, short timescales, and sporadic evidence of advective events (surface capping, intrusions of Levantine Intermediate Water (LIW)). Deep convection, reaching 1500 m, was observed in late February; by late April the field had not yet returned to its initial conditions (strong deficit of LIW). Comparison with available atmospheric flux data shows that advection acts to delay the occurence of convection and confirms the essential role of buoyancy fluxes. For this winter, the deep mixing results in an injection of anomalously warm water (ΔT≈0.03°) to a depth of 1500 m, compatible with the deep warming previously reported.
    Type: Article , PeerReviewed
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  • 9
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    American Meteorological Society
    In:  Journal of Physical Oceanography, 32 (3). pp. 891-902.
    Publication Date: 2018-04-06
    Description: The so-called equatorial stacked jets are analyzed with ship-board observations and moored time series from the Atlantic Ocean. The features are identified and isolated by comparing vertical wavenumber spectra at the equator with those a few degrees from the equator. Mode-filtering gives clear views of the jets in meridional sections, the typical extent being ±1° in latitude. The vertical structure can be well described (explaining 82% of the variance) by N−1-stretched cosines, with a Gaussian amplitude tapering in the vertical. The stretched wavelengths are somewhat variable. Fitting jets of a fixed (stretched) wavelength to four moored sensors in the depth range 1300–1900 m, allows one to track the vertical phase of the jets with an rms error of 30°–45°. The resulting fit from a 20-month moored time series shows long periods of unchanging jet conditions and intermittent times of high variability. There is no significant vertical propagation on these timescales nor a seasonal reversal. Using a composite from many different experiments, interannual variability is visible, however. A possible mechanism for the stacked jets is inertial instability, resulting from background meridional shears at the equator. A condition is that the Ertel potential vorticity becomes zero somewhere, due to meridional asymmetries in the zonal flows. The ship-board observations show that this may be approximately fulfilled by the instantaneous zonal low-mode flows at various depths, resulting from an excess of zonal momentum south of the equator most of the time. Inertial instability should act to redistribute this zonal momentum, and our mooring data show indeed persistent northward momentum flux, but not at the depth levels expected. The momentum transport might suggest that the jets can also flux or mix other properties across the equator.
    Type: Article , PeerReviewed
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  • 10
    Publication Date: 2018-06-15
    Description: Open-ocean deep convection is a littleunderstood process occurring in winter in remote areas under hostile observation conditions, for example, in the Labrador and Greenland Seas and near the Antarctic continent. Deep convection is a crucial link in the “Great Ocean Conveyor Belt” [Broecker, 1991], transforming poleward flowing warm surface waters through atmosphere-oceaninteraction into cold equatorward flowing water masses. Understanding its physics, interannual variations, and role in the global thermohaline circulation is an important objective of climate change research. In convection regions, drastic changes in water mass properties and distribution occur on scales of 10–100 km. These changes occur quickly and are difficult to observe with conventional oceanographic techniques. Apart from observing the development of the deep-mixed patch of homogeneous water itself, processes of interest are convective plumes on scales 〈1 km and vertical velocities of several cm s−1 [Schott et al., 1994] that quickly mix water masses vertically, and instability processes at the rim of the convection region that expedite horizontal exchanges of convected and background water masses [e.g., Gascard, 1978].
    Type: Article , NonPeerReviewed
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