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  • 1
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    An Energy Compartment Model for Propagation, Nonlinear Interaction, and Dissipation of Internal Gravity Waves (2014)
    American Meteorological Society
    In:  EPIC3Journal of Physical Oceanography, American Meteorological Society, 44(8), pp. 2093-2106, ISSN: 0022-3670
    Details
    Publication Date: 2019-07-16
    Description: The recently proposed Internal Wave Dissipation, Energy and Mixing (IDEMIX) model, describing the propagation and dissipation of internal gravity waves in the ocean, is extended. Compartments describing the energy contained in the internal tides and the near-inertial waves at low, vertical wavenumber are added to a compartment of the wave continuum at higher wavenumbers. Conservation equations for each compartment are derived based on integrated versions of the radiative transfer equation of weakly interacting waves. The compartments interact with each other by the scattering of tidal energy to the wave continuum by triad wave– wave interactions, which are strongly enhanced equatorward of 288 due to parametric subharmonic instability of the tide and by scattering to the continuum of both tidal and near-inertial wave energy over rough topography and at continental margins. Global numerical simulations of the resulting model using observed stratification, forcing functions, and bottom topography yield good agreement with available observations.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 2
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    The IDEMIX model: Parameterization of internal gravity waves for circulation models of ocean and atmosphere (2018)
    Springer Verlag
    In:  EPIC3Energy Transfers in Atmosphere and Ocean, Energy Transfers in Atmosphere and Ocean, Berlin, Springer Verlag, 41 p., pp. 87-127, ISBN: 978-3-030-05703-9
    Details
    Publication Date: 2019-04-01
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 3
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    A wind-driven model of the ocean surface layer with wave radiation physics (2020)
    SPRINGER HEIDELBERG
    In:  EPIC3Ocean Dynamics, SPRINGER HEIDELBERG, 70(8), pp. 1067-1088, ISSN: 1616-7341
    Details
    Publication Date: 2020-09-17
    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.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    The impact of advection schemes on restratifiction due to lateral shear and baroclinic instabilities (2015)
    ELSEVIER SCI LTD
    In:  EPIC3Ocean Modelling, ELSEVIER SCI LTD, 94, pp. 112-127, ISSN: 1463-5003
    Details
    Publication Date: 2017-01-27
    Description: This paper quantifies spurious dissipation and mixing of various advection schemes in idealised experiments of lateral shear and baroclinic instabilities in numerical simulations of a re-entrant Eady channel for configurations with large and small Rossby numbers. In addition, a two-dimensional barotropic shear instability test case is used to examine numerical dissipation of momentum advection in isolation, without any baroclinic effects. Effects of advection schemes on the evolution of background potential energy and the dynamics of the restratification process are analysed. The advection schemes for momentum and tracers are considered using several different methods including a recently developed local dissipation analysis. As highly accurate but computationally demanding schemes we apply WENO and MP5, and as more efficient lower-order total variation diminishing (TVD) schemes we use among others the SPL-max-View the MathML source13 and a third-order-upwind scheme. The analysis shows that the MP5 and SPL-max-View the MathML source13 schemes provide the most accurate results. Following our comprehensive analysis of computational costs, the MP5 scheme is approximately 2.3 times more expensive in our implementation. In contrast to the configuration with a small Rossby number, in which significant differences between schemes are apparent, the different advection schemes behave similarly for a larger Rossby number. Regions of high numerical dissipation are shown to be associated with low grid Reynolds numbers. The major outcome of the present study is that generally positive global numerical dissipation and positive background potential energy evolution delay the restratification process.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Revisiting the Generation of Internal Waves by Resonant Interaction with Surface Waves (2016)
    AMER METEOROLOGICAL SOC
    In:  EPIC3Journal of Physical Oceanography, AMER METEOROLOGICAL SOC, 46, pp. 2335-2350, ISSN: 0022-3670
    Details
    Publication Date: 2016-09-19
    Description: Two surface waves can interact to produce an internal gravity wave by nonlinear resonant coupling. The process has been called spontaneous creation (SC) because it operates without internal waves being initially present. Previous studies have shown that the generated internal waves have high frequency close to the local Brunt–Väisälä frequency and wavelengths that are much larger than those of the participating surface waves, and that the spectral transfer rate of energy to the internal wave field is small compared to other generation processes. The aim of the present analysis is to provide a global map of the energy transfer into the internal wave field by surface–internal wave interaction, which is found to be about 10 23 TW in total, based on a realistic wind-sea spectrum (depending on wind speed), mixed layer depths, and stratification below the mixed layer takenfrom a state-of-the-art numericalocean model.Unlikepreviouscalculationsof the spectral transfer rate based on a vertical mode decomposition, the authors use an analytical framework that directly derives the energy flux of generated internal waves radiating downward from the mixed layer base. Since the radiated waves are of high frequency, they are trapped and dissipated in the upper ocean. The radiative flux thus feeds only a small portion of the water column, unlike in cases of wind-driven near-inertial waves that spread over the entire ocean depth before dissipating. The authors also give an estimate of the interior dis- sipation and implied vertical diffusivities due to this process. In an extended appendix, they review the modal description of the SC interaction process, completed by the corresponding counterpart, the modulation in- teraction process (MI), where a preexisting internal wave is modulated by a surface wave and interacts with another one. MI establishes a damping of the internal wave field, thus acting against SC. The authors show that SC overcomes MI for wind speeds exceeding about 10m/s.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Evaluating the Global Internal Wave Model IDEMIX Using Finestructure Methods (2017)
    AMER METEOROLOGICAL SOC
    In:  EPIC3Journal of Physical Oceanography, AMER METEOROLOGICAL SOC, 47, pp. 2267-2289, ISSN: 0022-3670
    Details
    Publication Date: 2017-10-12
    Description: Small-scale turbulent mixing affects large-scale ocean processes such as the global overturning circulation but remains unresolvedin ocean models. Since the breaking of internal gravity waves is a major source of this mixing, consistent parameterizations take internal wave energetics into account. The model Internal Wave Dissipation,EnergyandMixing(IDEMIX)predictstheinternalwaveenergy,dissipationrates,anddiapycnal diffusivities based on a simplification of the spectral radiation balance of the wave field and can be used as a mixing module in global numerical simulations. In this study, it is evaluated against finestructure estimates of turbulent dissipation rates derived from Argo float observations. In addition, a novel method to compute internal gravity wave energy from finescale strain information alone is presented and applied. IDEMIX well reproducesthe magnitudeandthelarge-scalevariations ofthe Argo-derived dissipationrateandenergylevel estimates. Deficiencies arise with respect to the detailed vertical structure or the spatial extent of mixing hot spots. This points toward the need to improve the forcing functions in IDEMIX, both by implementing additionalphysicaldetailandbybetterconstrainingtheprocessesalreadyincludedinthemodel.Aprominent example is the energy transfer from the mesoscale eddies to the internal gravity waves, which is identified as an essential contributor to turbulent mixing in idealized simulations but needs to be better understood through the help of numerical, analytical, and observational studies in order to be represented realistically in ocean models.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 7
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    Impact of advection schemes on restratification (2017)
    In:  EPIC349th International Liege colloquium, Liege, 2017-05-22-2017-05-26
    Details
    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 , notRev
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  • 8
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    Challenges and Prospects in Ocean Circulation Models (2020)
    Details
    Publication Date: 2020-03-12
    Description: We revisit the challenges and prospects for ocean circulation models following Griffies et al. (2010). Over the past decade, ocean circulation models evolved through improved understanding, numerics, spatial discretization, grid configurations, parameterizations, data assimilation, environmental monitoring, and process-level observations and modeling. Important large scale applications over the last decade are simulations of the Southern Ocean, the Meridional Overturning Circulation and its variability, and regional sea level change. Submesoscale variability is now routinely resolved in process models and permitted in a few global models, and submesoscale effects are parameterized in most global models. The scales where nonhydrostatic effects become important are beginning to be resolved in regional and process models. Coupling to sea ice, ice shelves, and high-resolution atmospheric models has stimulated new ideas and driven improvements in numerics. Observations have provided insight into turbulence and mixing around the globe and its consequences are assessed through perturbed physics models. Relatedly, parameterizations of the mixing and overturning processes in boundary layers and the ocean interior have improved. New diagnostics being used for evaluating models alongside present and novel observations are briefly referenced. The overall goal is summarizing new developments in ocean modeling, including: how new and existing observations can be used, what modeling challenges remain, and how simulations can be used to support observations
    Description: Published
    Description: Article 65
    Description: 4A. Oceanografia e clima
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    IDEMIX: a model of internal gravity wave energetics and diapycnal mixing (solicited) (2015)
    In:  EPIC3EGU General Assembly, OS5.1/AS4.3, 2015-04-14
    Details
    Publication Date: 2015-04-28
    Description: Breaking of internal gravity waves is a major source of diapycnal mixing, driving the large-scale circulation. An energetically consistent model of the diapycnal diffusivity requires a closed model of the wave energetics, including generation, non-linear transfer and dissipation. IDEMIX meets this requirement by heavy truncation of the radiation balance equation: the energetics are formulated for a small number of compartments as integrals over respective parts of the spectral wavenumber space. The current version has compartments for up- and downward propagating waves in the frequency-wavenumber continuum and low-mode near-inertial and tidal waves. Forcing occurs by radiation of wind-driven near-inertial waves from the surface mixed layer and barotropic to baroclinic conversion of tidal energy at submarine topography. The compartments are coupled by wave-wave interactions and bottom scattering. Energy transferred by wave-wave interactions to high wavenumbers is dissipated and partly used for mixing. The model is working in physical space - the global ocean - with wave propagation by mean group velocities. IDEMIX has been studied as stand-alone module (using a Brunt-Väisälä frequency climatology and the Osborn-Cox relation to infer diapycnal diffusivities) and in a coupled mode in a global OGCM. The inferred diapycnal diffusivities have a reasonable size and plausible spatial pattern. We report on new developments in IDEMIX as the incorporation of topographic lee-waves and wave-mean flow interaction.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 10
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    A Global Model for the Diapycnal Diffusivity Induced by Internal Gravity Waves (2013)
    AMER METEOROLOGICAL SOC
    In:  EPIC3Journal of Physical Oceanography, AMER METEOROLOGICAL SOC, 43(8), pp. 1759-1779, ISSN: 0022-3670
    Details
    Publication Date: 2019-07-16
    Description: An energetically consistent model for the diapycnal diffusivity induced by breaking of internal gravity waves is proposed and tested in local and global settings. The model [Internal Wave Dissipation, Energy and Mixing (IDEMIX)] is based on the spectral radiation balance of the wave field, reduced by integration over the wavenumber space, which yields a set of balances for energydensity variables in physical space. A further simplification results in a single partial differentialequation for the total energy density of the wave field. The flux of energy to high vertical wavenumbers is parameterized by a functional derived from the wave–wave scattering integral of resonant wave triad interactions, which also forms the basis for estimates of dissipation rates and related diffusivities of ADCP and hydrography fine-structure data. In the current version of IDEMIX,thewaveenergyisforcedbywind-drivennear-inertialmotionsandbaroclinictides,radiatingwaves from the respectiveboundarylayers at the surfaceand the bottom into the ocean interior. The model predicts plausible magnitudes and three-dimensional structures of internal wave energy, dissipation rates, and dia- pycnal diffusivities in rough agreement to observational estimates. IDEMIX is ready for use as a mixing module in ocean circulation models and can be extended with more spectral components.
    Repository Name: EPIC Alfred Wegener Institut
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