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  • 1
    Series available for loan
    Series available for loan
    Warnemünde : Institut für Ostseeforschung
    Associated volumes
    Call number: ZS-000(63)
    In: Meereswissenschaftliche Berichte
    Type of Medium: Series available for loan
    Pages: 274 S. , graph. Darst.
    Series Statement: Meereswissenschaftliche Berichte 63
    Classification: D.3.
    Location: Lower compact magazine
    Branch Library: GFZ Library
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  • 2
    Publication Date: 2017-10-12
    Description: A host of studies has recognized that truncation errors of the discretized advection terms lead to spurious mixing and dissipation (Fig. 1) and may interact nonlinearly with turbulent mixing and transport. To investigate the impacts of spurious mixing and dissipation, we implemented some of the most novel advection schemes into the coastal ocean model GETM. We quantified spurious dissipation [Klingbeil, 2014] and mixing of the advection schemes (Fig. 3) in idealized experiments of baroclinic instabilities (Fig. 2) ranging from mesoscales (small Rossby number) to sub-mesoscales (order-one Rossby number). The processes at submesosales are distinct from mesoscale by their contribution to restratification of the mixed layer. Such analyses (Fig. 4) help to choose between highly accurate but complex schemes and lower-order less complex schemes balancing accuracy and computational costs. The major outcome of the present study is that both, numerically induced dissipation (leading to a decrease of kinetic energy) and numerically induced mixing (leading to an increase of background potential energy), artificially delay the restratification process [Mohammadi-Aragh, 2015], an effect that needs to be taken into account if parameterizations for eddy-induced mixing and dissipation are compared with numerical model simulations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
    Format: application/pdf
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  • 3
    Publication Date: 2017-01-27
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2017-02-14
    Description: The discretisation of the advection terms in transport equations introduces truncation errors in numerical models. These errors are usually associated with spurious diffusion, i.e. numerically-induced mixing of the advected quantities or dissipation of kinetic energy associated with the advection of momentum. Especially the numerically-induced diapycnal mixing part is very problematic for realistic model simulations. Since any diapycnal mixing of temperature and salinity increases the reference potential energy (RPE), numerically-induced mixing is often quantified in terms of RPE. However, this global bulk measure does not provide any information about the local amount of numerically-induced mixing of a single advected quantity. In this talk we will present a recently developed analysis method that quantifies the numerically-induced mixing of a single advected quantity locally (Klingbeil et al., 2014***). The method is based on the local tracer variance decay in terms of variance fluxes associated with the corresponding advective tracer fluxes. Because of its physically sound definition, this analysis method provides a reliable diagnostic tool, e.g., to assess the performance of advection schemes and to identify hotspots of numerically-induced mixing. At these identified positions the model could be adapted in terms of resolution or the applied numerical schemes. In this context we will demonstrate how numerically-induced mixing of temperature and salinity can be substantially reduced by vertical meshes adapting towards stratification. *** Klingbeil, K., M. Mohammadi-Aragh, U. Gräwe, H. Burchard (2014) . Quantification of spurious dissipation and mixing – Discrete Variance Decay in a Finite-Volume framework. Ocean Modelling. doi:10.1016/j.ocemod.2014.06.001.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
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    Elsevier
    In:  Ecological Modelling, 221 (2). pp. 238-244.
    Publication Date: 2012-12-06
    Description: There is an increasing need to describe cyanobacteria bloom dynamics using ecosystem models. We consider two fundamentally different ways how cyanobacteria are currently implemented: a simple approach without explicit consideration of the life cycle which assumes that cyanobacteria grow due to nitrogen fixation alone and an advanced approach that computes the succession of four different stages of the cyanobacteria life cycle based on internal quotas of energy and nitrogen. To qualitatively and quantitatively intercompare these different approaches and with observations, we use the Baltic Sea ecosystem model ERGOM coupled to the one-dimensional water column model GOTM. Four experiments are carried out: three, using the simple approach with either (a) a prescribed constant minimum production, (b) no minimum value or (c) a prescribed constant minimum concentration, and one with (d) the full predictive life cycle. The model data of 35 years (1970-2005) are analyzed for the timing of the bloom, the interannual variability, the annual mean nitrogen fixation rates and the effect of cyanobacteria on eukaryotic phytoplankton. The results show significant differences. In the climatological seasonal mean, only the advanced approach which resolves the life cycle produces a realistic bloom onset and duration. The interannual variability of blooms is unrealistically small in the experiments with a prescribed minimum value. Annual mean nitrogen fixation rates diverge by up to 30% between the four model solutions. Finally, the representation of the cyanobacteria also influences the seasonal cycle of eukaryotic phytoplankton, i.e., flagellates. This study demonstrates that the way how cyanobacteria are implemented in coupled biological-physical models strongly determines the fluxes into the system and between the individual compartments.
    Type: Article , PeerReviewed
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  • 6
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    Hamburg: Verlag Weltarchiv | ZBW – Leibniz Information Centre for Economics Kiel, Hamburg
    Publication Date: 2018-09-10
    Keywords: ddc:330
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: German
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  • 7
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    Hamburg: Verlag Weltarchiv | ZBW – Leibniz Information Centre for Economics Kiel, Hamburg
    Publication Date: 2018-09-10
    Keywords: ddc:330
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: German
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  • 8
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    Hamburg: Verlag Weltarchiv | ZBW – Leibniz Information Centre for Economics Kiel, Hamburg
    Publication Date: 2018-09-10
    Keywords: ddc:330
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: German
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  • 9
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0271-2091
    Keywords: 3D modelling systems ; general vertical co-ordinates ; pressure gradient ; hydrostatic consistency ; momentum advection ; Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: It is discussed in this paper how the pressure gradient error in general vertical co-ordinate models (in which the σ-transformation is a special case) can be reduced by means of hybrid models. For a better understanding, the derivation of such a general vertical co-ordinate model from the Cartesian co-ordinate model is given. Two types of hybridization between σ- and z-co-ordinate models, each using one parameter specifying the degree of hydridization, are presented: (i) the mixed layer transformation with a constant number of layers which are refined near the surface and (ii) the z/σ-transformation which introduces steps near the bottom. In order to achieve good results with the models using other than σ-co-ordinates, a profile-conserving momentum advection discretization is developed. The different co-ordinate transformations are tested with 2D barotropic and baroclinic flows over a topographic bump. Those models with nearly horizontal co-ordinate surfaces in the stratified area give the best correspondence with an isopycnal reference solution. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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