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  • 11
    In: Spektrum der Wissenschaft, Heidelberg : Spektrum-der-Wiss.-Verl.-Ges., 1978, (2005), 6, Seite 16-20, 0170-2971
    In: year:2005
    In: number:6
    In: pages:16-20
    In: extent:3
    Type of Medium: Article
    Pages: 3 , Zahlr. Ill.
    ISSN: 0170-2971
    Language: German
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  • 12
    Description / Table of Contents: This book describes a recent effort combining interdisciplinary expertise within the Collaborative Research Centre “Energy transfers in atmosphere and ocean” (TRR-181), which was funded by the German Research Foundation (DFG). Energy transfers between the three dynamical regimes - small-scale turbulence, internal gravity waves and geostrophically balanced motion - are fundamental to the energy cycle of both the atmosphere and the ocean. Nonetheless, they remain poorly understood and quantified, and have yet to be adequately represented in today’s climate models. Since interactions between the dynamical regimes ultimately link the smallest scales to the largest ones through a range of complex processes, understanding these interactions is essential to constructing atmosphere and ocean models and to predicting the future climate. To this end, TRR 181 combines expertise in applied mathematics, meteorology, and physical oceanography. This book provides an overview of representative specific topics addressed by TRR 181, ranging from - a review of a coherent hierarchy of models using consistent scaling and approximations, and revealing the underlying Hamiltonian structure - a systematic derivation and implementation of stochastic and backscatter parameterisations - an exploration of the dissipation of large-scale mean or eddying balanced flow and ocean eddy parameterisations; and - a study on gravity wave breaking and mixing, the interaction of waves with the mean flow and stratification, wave-wave interactions and gravity wave parameterisations to topics of a more numerical nature such as the spurious mixing and dissipation of advection schemes, and direct numerical simulations of surface waves at the air-sea interface. In TRR 181, the process-oriented topics presented here are complemented by an operationally oriented synthesis focusing on two climate models currently being developed in Germany. In this way, the goal of TRR 181 is to help reduce the biases in and increase the accuracy of atmosphere and ocean models, and ultimately to improve climate models and climate predictions
    Type of Medium: Book
    Pages: xvi, 312 Seiten , Illustrationen, Diagramme
    ISBN: 9783030057039
    Series Statement: Mathematics of Planet Earth volume 1
    RVK:
    Language: English
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  • 13
    Keywords: Hochschulschrift ; Antarktischer Zirkumpolar-Strom
    Type of Medium: Online Resource
    Pages: Online-Ressource
    DDC: 550
    Language: English
    Note: Kiel, Univ., Diss., 2012
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  • 14
    Keywords: Hochschulschrift
    Type of Medium: Online Resource
    Pages: 1 Online-Ressource (74 Seiten = 3,4 MB) , Illustrationen, Graphen
    Language: English
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  • 15
    Online Resource
    Online Resource
    Cham :Springer International Publishing AG,
    Keywords: Energy transfer-Mathematical models. ; Electronic books.
    Type of Medium: Online Resource
    Pages: 1 online resource (323 pages)
    Edition: 1st ed.
    ISBN: 9783030057046
    Series Statement: Mathematics of Planet Earth Series ; v.1
    DDC: 541.22
    Language: English
    Note: Intro -- Preface -- Acknowledgements -- Contents -- Contributors -- 1 Multi-scale Methods for Geophysical Flows -- 1.1 Introduction -- 1.2 The Governing Equations -- 1.2.1 Rotating Boussinesq Equations -- 1.2.2 Imbalance Variables -- 1.2.3 Mid-latitude Scalings -- 1.2.4 Hydrostatic Approximation -- 1.2.5 The Quasi-geostrophic Approximation on the β-plane -- 1.2.6 Rotating Shallow Water Equations -- 1.2.7 Geostrophic Scalings -- 1.2.8 Equatorial Scalings -- 1.3 Variational Principles and Hamiltonian Mechanics -- 1.3.1 Variational Principles -- 1.3.2 Variational Model Reduction -- 1.3.3 Poisson Formulation -- 1.3.4 Nambu Formulation -- 1.4 Dissipation, Turbulence, and Nonlinear Waves -- 1.4.1 Viscosity and Dissipation -- 1.4.2 Nonlinear Waves and Dynamical Systems Methods -- 1.5 Stochastic Model Reduction -- 1.5.1 Basic Setup -- 1.5.2 Slow Dynamics via the Kolmogorov Backward Equation -- 1.5.3 Direct Averaging -- 1.6 Outlook -- References -- 2 The Interior Energy Pathway: Inertia-Gravity Wave Emission by Oceanic Flows -- 2.1 Introduction -- 2.2 Rotating Shallow Water Equations and Spontaneous Emission -- 2.2.1 Shallow Water on the f-Plane -- 2.2.2 Spontaneous Emission -- 2.2.3 Beyond Shallow Water -- 2.3 Ray Equations and Wave Capture -- 2.4 Interactions Between IGWs and Density Fronts -- 2.4.1 Wave Capture in Frontal Strain -- 2.4.2 Role of IGWs in Frontal Geostrophic Adjustment -- 2.5 Diagnostics -- 2.5.1 Characterization of Flow Regimes via the Rossby Number -- 2.5.2 Linear Filters -- 2.5.3 Optimal Potential Vorticity Balance -- 2.5.4 A Simple Model for Optimal Balance -- 2.6 High-resolution Ocean General Circulation Models as a Novel Tool for Studying Spontaneous Emission -- 2.7 Discussion -- References -- 3 The IDEMIX Model: Parameterization of Internal Gravity Waves for Circulation Models of Ocean and Atmosphere. , 3.1 Internal Waves in Ocean and Atmosphere -- 3.2 The IDEMIX Model -- 3.2.1 Details of the Oceanic IDEMIX -- 3.2.2 The IDEMIX Concept Applied to Atmospheric Gravity Waves -- 3.3 Oceanic Processes in Present and Future IDEMIX -- 3.3.1 Including Energy Transfers from Mesoscale Eddies to Internal Waves -- 3.3.2 Including Wave-Mean Flow Interaction -- 3.3.3 Including Anisotropic Tidal Forcing -- 3.3.4 Including High-Frequency Compartments -- 3.3.5 Evaluation with Available Observations -- 3.4 Atmospheric Processes in IDEMIX -- 3.5 Summary -- References -- 4 Observations and Models of Low-Mode Internal Waves in the Ocean -- 4.1 Introduction -- 4.2 Numerical Modeling -- 4.2.1 Wind -- 4.2.2 Tides -- 4.3 Dissipation -- 4.4 Observations -- 4.4.1 Satellite Altimetry -- 4.4.2 Shipboard Observations -- 4.4.3 Moorings -- 4.5 Summary and Outlook -- References -- 5 Toward Consistent Subgrid Momentum Closures in Ocean Models -- 5.1 Introduction -- 5.2 Subgrid Momentum Closures -- 5.3 Quasigeostrophic Turbulence and Ocean Eddies -- 5.3.1 Two-Dimensional Turbulence -- 5.3.2 Two-Layer Geostrophic Flows -- 5.3.3 Continuously Stratified and Surface QG Dynamics -- 5.3.4 Ocean Models and Observational Evidence -- 5.4 Energy Backscatter -- 5.4.1 Models with Scalar Subgrid Energy Budget -- 5.4.2 Stochastic Superparameterizations -- 5.5 Other Closures -- 5.5.1 The Mana-Zanna Parameterization of Ocean Mesoscale Eddies -- 5.5.2 α-Models -- 5.6 Concluding Remarks -- References -- 6 Diagnosing and Parameterizing the Effects of Oceanic Eddies -- 6.1 Introduction -- 6.1.1 Isopycnal and Diapycnal Diffusion -- 6.1.2 Skew Diffusion -- 6.1.3 Diagnosing and Parameterizing the Diffusivities -- 6.2 Eddy Diffusivity Diagnostics -- 6.2.1 Lagrangian Particle Dispersion -- 6.2.2 Quasigeostrophic Linear Stability Analysis -- 6.2.3 Diffusivities from Eulerian Eddy Fluxes. , 6.3 Eddy Diffusivity Estimates in the Global Ocean -- 6.4 Limits of the Eddy Diffusion Model and Anomalous Diffusion -- 6.5 Eddy Diffusivity Parameterization -- 6.5.1 EKE Equation -- 6.6 Conclusions -- References -- 7 Entropy Production in Turbulence Parameterizations -- 7.1 The Numerically Modeled Atmosphere as a Forced-Dissipative System -- 7.2 The Entropy Budget Equation in Numerical Models of the Atmosphere -- 7.3 Moisture and Precipitation Fluxes -- 7.4 Thermal Fluxes -- 7.5 Momentum Fluxes -- 7.6 Fluctuation Theorem -- 7.7 Applicability of the Fluctuation Theorem in Geophysical Flows -- References -- 8 Reducing Spurious Diapycnal Mixing in Ocean Models -- 8.1 Introduction -- 8.2 Diagnosing Spurious Mixing -- 8.2.1 An Analytical Example -- 8.2.2 Variance Decay as a Measure for Mixing and Dissipation -- 8.2.3 Discrete Variance Decay -- 8.2.4 Applications -- 8.3 Arbitrary Lagrangian Eulerian Vertical Coordinate -- 8.3.1 tildez-Vertical Coordinate and its Effect on Spurious Mixing -- 8.3.2 Additional Techniques for Adaptive Vertical Model Layers -- 8.4 Advection Algorithms Stabilized with Isoneutral Mixing -- 8.5 ADER High Order Flux Evaluation and WENO Reconstruction -- 8.5.1 The Generalized Riemann Problem -- 8.5.2 Kernel-Based WENO Reconstruction -- 8.6 Discussion and Conclusions -- References -- 9 Diffuse Interface Approaches in Atmosphere and Ocean-Modeling and Numerical Implementation -- 9.1 Introduction -- 9.2 Diffuse Interface Approach -- 9.2.1 Notation -- 9.2.2 The Mathematical Model -- 9.3 Discretization -- 9.3.1 The Temporal Discretization -- 9.3.2 The Spatial Discretization and Energy Inequalities -- 9.3.3 A posteriori Error Estimation -- 9.4 Numerics -- 9.5 Outlook on the Direction of Research -- References -- Index.
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  • 16
    Publication Date: 2023-06-21
    Description: Surface windstress transfers energy to the surface mixed layer of the ocean, and this energy partly radiates as internal gravity waves with near-inertial frequencies into the stratified ocean below the mixed layer where it is available for mixing. Numerical and analytical models provide estimates of the energy transfer into the mixed layer and the fraction radiated into the interior, but with large uncertainties, which we aim to reduce in the present study. An analytical slab model of the mixed layer used before in several studies is extended by consistent physics of wave radiation into the interior. Rayleigh damping, controlling the physics of the original slab model, is absent in the extended model and the wave-induced pressure gradient is resolved. The extended model predicts the energy transfer rates, both in physical and wavenumber-frequency space, associated with the wind forcing, dissipation in the mixed layer, and wave radiation at the base as function of a few parameters: mixed layer depth, Coriolis frequency and Brunt-Väisälä frequency below the mixed layer, and parameters of the applied windstress spectrum. The results of the model are satisfactorily validated with a realistic numerical model of the North Atlantic Ocean.
    Description: Deutsche Forschungsgemeinschaft https://doi.org/10.13039/501100001659
    Keywords: ddc:551.5 ; Wind-driven internal gravity waves ; Wave radiation physics
    Language: English
    Type: doc-type:article
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  • 17
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 41 (11). pp. 2242-2258.
    Publication Date: 2018-04-12
    Description: Simple idealized layered models and primitive equation models show that the meridional gradient of the zonally averaged pressure has no direct relation with the meridional flow. This demonstrates a contradiction in an often-used parameterization in zonally averaged models. The failure of this parameterization reflects the inconsistency between the model of Stommel and Arons and the box model of Stommel, as previously pointed out by Straub. A new closure is proposed. The ocean is divided in two dynamically different regimes: a narrow western boundary layer and an interior ocean; zonally averaged quantities over these regions are considered. In the averaged equations three unknowns appear: the interior zonal pressure difference Delta p(i), the zonal pressure difference Delta p(b) of the boundary layer, and the zonal velocity us at the interface between the two regions. Here Delta p(i) is parameterized using a frictionless vorticity balance, Delta p(b), by the difference of the mean pressure in the interior and western boundary, and u(delta) by the mean zonal velocity of the western boundary layer. Zonally resolved models, a layer model, and a primitive equation model validate the new parameterization by comparing with the respective zonally averaged counterparts. It turns out that the zonally averaged models reproduce well the buoyancy distribution and the meridional flow in the zonally resolved model versions with respect to the mean and time changes.
    Type: Article , PeerReviewed
    Format: text
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  • 18
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    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 44 (2). pp. 445-463.
    Publication Date: 2020-08-04
    Description: Mooring observations and model simulations point to an instability of the Labrador Current (LC) during winter, with enhanced eddy kinetic energy (EKE) at periods between 2 to 5 days, and much less EKE during other seasons. Linear stability analysis using vertical shear and stratification from the model reveals three dominant modes of instability in the LC: - a balanced interior mode with along-flow wavelengths of about 30–45 km, phase velocities of 0.3 m/s, maximal growth rates of 1 d−1 and surface intensified, but deep reaching amplitudes, - a balanced shallow mode with along-flow wavelengths of about 0.3–1.5 km, about three times larger phase speeds and growth rates, but amplitudes confined to the mixed layer (ML), - and an unbalanced symmetric mode with largest growth rates, vanishing phase speeds and along-flow structure, and very small cross-flow wavelengths, also confined to the ML. Both balanced modes are akin to baroclinic instability, but operate at moderate to small Richardson numbers Ri with much larger growth rates as for the quasi-geostrophic limit of Ri ≫ 1. The interior mode is found to be responsible for the instability of the LC during winter. Weak stratification and enhanced vertical shear due to local buoyancy loss and the advection of convective water masses from the interior result in small Ri within the LC, and to three times larger growth rates of the interior mode in March compared to summer and fall conditions. Both the shallow and the symmetric mode are not resolved by the model, but it is suggested that they might also play an important role for the instability in the LC and for lateral mixing.
    Type: Article , PeerReviewed
    Format: text
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  • 19
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    Elsevier
    In:  Deep Sea Research Part II: Topical Studies in Oceanography, 46 . pp. 33-54.
    Publication Date: 2019-09-23
    Description: The possibilities of defining and computing an approximately neutral density variable are reexamined in this paper. There are three desirable properties that a neutral density variable should possess. Firstly, the isosurfaces of this variable should coincide with (approximately) neutral surfaces. This would facilitate the analysis of hydrographic data on the most appropriate mixing and spreading surfaces. Secondly, the horizontal gradients of the neutral density should agree with the gradients of the in situ density, and thirdly the vertical gradient of the neutral density variable should be proportional to the static stability of the water column. A density variable that approximates the latter two properties can be used in ocean circulation models based on layer coordinates, and would reduce substantial errors in present isopycnal models due to the use of a potential density variable. No variable can possess all the three properties simultaneously. The variable γn introduced by Jackett and McDougall (1997, J. Phys. Oceanogr. 27, 237–263) satisfies the first of the properties exactly but is not designed for the use in models. Based on climatological data in the North Atlantic, an alternative neutral density variable ν̃(S, Θ) is defined, which is shown to approximate the two gradient criteria much better than any potential density. We suggest that this neutral density variable may be useful in isopycnal ocean models as an alternative to potential density, since it could significantly reduce errors in thermal wind relation and vertical stability
    Type: Article , PeerReviewed
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  • 20
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    Elsevier
    In:  Ocean Modelling, 34 (3-4). pp. 150-165.
    Publication Date: 2019-01-23
    Description: The sensitivity of the meridional overturning circulation (MOC) of the Southern Ocean (SO) to wind stress changes is discussed. Using an idealised SO model in both non- and eddy-permitting configurations, we assess the effects of both, coarsening the horizontal resolution and implementing different parameterisations for the lateral eddy diffusivity appropriate to the Gent and McWilliams (1990) parameterisation, K. We find that the MOC is characterised by an eddy-driven part ψ* which generally opposes the wind-driven part and that the increase of the MOC diminishes with amplifying winds, with the possibility that the MOC in the SO may become completely insensitive to wind stress changes. However, for moderate wind stress, the MOC is still significantly increasing in our configuration. The diagnosed lateral eddy diffusivity K in the eddy-permitting version shows strong spatial variability and is increasing with increasing wind stress. Similar to the MOC (but in contrast to ψ*) the increase of K diminishes with amplifying winds. It turns out that a small increase in the isopycnal slopes is also relevant in order to capture the correct sensitivity of ψ* on wind stress. This relation also holds in model configurations with coarser but still eddy-permitting horizontal resolution: decreasing the horizontal resolution decreases K, but increases the isopycnal slopes such that the strength of the MOC including its sensitivity to wind stress is almost unchanged. The parameterisations are able to reproduce the MOC for certain wind stresses, but all parameterisations underestimate the sensitivity of K and thus overestimate the sensitivity of the MOC on wind stress. Our results show that it is indispensable to incorporate the correct sensitivity of K into climate models in order to reproduce the correct sensitivity of the MOC to wind stress and that up-to-date parameterisations for K are only partially successful.
    Type: Article , PeerReviewed
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