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  • 1
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    Variability of the Great Whirl from Observations and Models (2002)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 49 (7). pp. 1279-1295.
    Details
    Publication Date: 2020-08-05
    Description: Observations from cruises in the Arabian Sea and data from satellites are interpreted using different realizations of a multi-level primitive equation model and an eddy-permitting reduced-gravity shallow water model of the Indian Ocean. The focus is on the interannual circulation variability of the Arabian Sea, and especially of the meridional location of the Great Whirl (GW). The results suggest that the variability in the western Arabian Sea is not only due to the interannual variability in the wind field, but that a substantial part is caused by the chaotic nature of the ocean dynamics. Decreasing the friction coefficient from 1000 to 500m2s-1 in a 19o numerical reduced-gravity model, the variance of the GW location increases dramatically, and the mean position moves southward by one degree. In the eddy-permitting experiments analyzed, both mechanisms appear to determine the GW location at the onset of the GW dynamics in late summer.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(01)00165-5
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Friedrich A. Schott (1939-2008) (2008)
    AGU (American Geophysical Union)
    In:  Eos, Transactions American Geophysical Union, 89 (41). p. 391.
    Details
    Publication Date: 2017-02-24
    Description: The physical oceanography community recently lost one of its most influential and productive scientists. Friedrich A. (“Fritz”) Schott, who had been fighting leukemia for about a year, died on 30 April 2008 at the age of 69.
    Type: Article , NonPeerReviewed
    Format: text
    DOI: 10.1029/2008EO410005
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    OceanRep: Article in a Scientific Journal - without review
  • 3
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    Variational assimilation of SSH variance from TOPEX/POSEIDON and ERS1 into an eddypermitting model of the North Atlantic (2000)
    CLIVAR
    In:  CLIVAR Exchanges, 17 (5 (3)). pp. 14-21.
    Details
    Publication Date: 2019-02-01
    Type: Article , NonPeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    The annual review of CLIVAR by the SSG (2003)
    CLIVAR
    In:  CLIVAR Exchanges, 26 (8 (2-3)). pp. 3-5.
    Details
    Publication Date: 2019-02-01
    Type: Article , NonPeerReviewed
    Format: text
    Location Call Number Limitation Availability
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    OceanRep: Article in a Scientific Journal - without review
  • 5
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    Parameter estimates of a zero-dimensional ecosystem model applying the adjoint method (2001)
    Pergamon Press
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 48 . pp. 1769-1800.
    Details
    Publication Date: 2020-08-05
    Description: Assimilation experiments with data from the Bermuda Atlantic Time-series Study (BATS, 1989¯1993) were performed with a simple mixed-layer ecosystem model of dissolvedinorganic nitrogen (N), phytoplankton (P) and herbivorous zooplankton (H). Our aim is to optimize the biological model parameters, such that the misfits between model results andobservations are minimized. The utilized assimilation method is the variational adjoint technique, starting from a wide range of first-parameter guesses. A twin experiment displayedtwo kinds of solutions, when Gaussian noise was added to the model-generated data. The expected solution refers to the global minimum of the misfit model-data function, whereasthe other solution is biologically implausible and is associated with a local minimum. Experiments with real data showed either bottom-up or top-down controlled ecosystemdynamics, depending on the deep nutrient availability. To confine the solutions, an additional constraint on zooplankton biomass was added to the optimization procedure. Thisinclusion did not produce optimal model results that were consistent with observations. The modelled zooplankton biomass still exceeded the observations. From the model-datadiscrepancies systematic model errors could be determined, in particular when the chlorophyll concentration started to decline before primary production reached its maximum. Adirect comparision of measured 14C-production data with modelled phytoplankton production rates is inadequate at BATS, at least when a constant carbon to nitrogen C : N ratio isassumed for data assimilation.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/S0967-0645(00)00161-2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Decadal to Multidecadal Variability of the Atlantic MOC: Mechanisms and Predictability (2007)
    AGU (American Geophysical Union)
    In:  In: Ocean Circulation: Mechanisms and Impacts - Past and Future Changes of the Ocean's Meridional Overturning. , ed. by Schmittner, A., Chiang, J. and Hemming, S. AGU Monograph, 173 . AGU (American Geophysical Union), Washington D.C., pp. 149-166. ISBN 978-0-87590-438-2
    Details
    Publication Date: 2020-07-28
    Description: The dynamics and predictability of the decadal to multidecadal Atlantic merid­ional overturning circulation (MOC) variability are described from observations and models. The investigation focuses on two modes that involve the MOC: One mode exhibits a quasi-decadal period, while the other is multidecadal. The two modes have completely different underlying dynamics, which is reflected in their rather different spatial characteristics. While the quasi-decadal mode represents a damped mode of the coupled ocean-atmosphere system, the multidecadal mode can be basically understood as the MOC response to the multidecadal forcing by the North Atlantic Oscillation (NAO). "Perfect model" predictability studies indicate a rather high predictability potential of the MOC variability on decadal timescales. Variations of the MOC are associated with variations in the meridional heat trans­port that drive sea surface temperature (SST) anomalies. SST anomalies in the North Atlantic thus exhibit a similar decadal predictability potential as the MOC. The decadal predictability carries over to the atmosphere. The probability density function of European surface air temperature anomalies, for instance, changes sig­nificantly with the state of the MOC. A reconstruction of the MOC for the 20th cen­tury from observed SSTs shows considerable variability on decadal timescales, but no strong sustained long-term trend. Furthermore, an assessment of the observed hydrographical changes in the Nordic Seas, with the aid of ocean general circula­tion model experiments and the analysis of recent scenario integrations with global climate models, indicates that the expected anthropogenic weakening of the MOC may not exceed the level of the internal variability within the next decades.
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 7
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    Variational assimilation of SSH variability from TOPEX/POSEIDON and ERSI into an eddy-permitting model of the North Atlantic (2003)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 108 (C3). p. 3092.
    Details
    Publication Date: 2019-04-04
    Description: A first step for improving the climatological state of high‐resolution general circulation models by means of data assimilation is presented. A method developed for the assimilation of statistical characteristics into chaotic ocean models is applied to assimilate SSH variability from TOPEX/POSEIDON and ERS1 in association with temperature and salinity from the World Ocean Atlas 1997 in order to estimate the underlying mean circulation. The method requires a parameterization of SSH variability which derives from the approach of Green and Stone. By estimating initial conditions for temperature and salinity, a mean state is achieved which, although not fully consistent with the altimetric and climatological data, is markedly improved on time scales of one year in comparison to the control run. The assimilation of SSH variability data introduces complementary information about the main frontal structures consistent with climatological observations. The state is however not an equilibrium state and returns back to the first guess quasi‐equilibrium state for longer integration periods.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2001JC000982
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Assimilation of Geosat altimeter data into an eddy-resolving primitive equation model of the North Atlantic Ocean (1996)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 101 (C6). pp. 14175-14190.
    Details
    Publication Date: 2019-09-23
    Description: We present a new method for assimilating observations of sea surface height (SSH) into a high‐resolution primitive equation model. The method is based on the concept of reinitialization. First, the surface velocity increments necessary to adjust the model forecast to the observed geostrophic surface currents are projected onto deep velocity increments by a linear regression method. Second, changes in the density field required to balance the changes in the velocity field geostrophically are obtained from an inversion of the thermal wind equation. A unique partition of the density increments into corresponding temperature and salinity changes is realized by conserving the local θ‐S relation of the model forecast. In contrast to pure statistical methods that infer temperature and salinity changes from correlations with SSH anomalies, our approach explicitly conserves water mass properties on isopycnals. For the assimilation experiment we use optimally interpolated maps of Geosat SSH anomalies (the mean topography is taken from the model), which are assimilated into the World Ocean Circulation Experiment (WOCE) Community Modeling Effort (CME) model of the North Atlantic Ocean at 5‐day intervals covering the year 1987. It is shown that the assimilation significantly improves the model's representation of eddy activity, with the hydrographic structure of individual eddies agreeing well with independent hydrographic observations. The importance of a careful treatment of water mass properties in the assimilation process is discussed and further illustrated by comparing different assimilation schemes.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/95JC03801
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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