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  • 1
    Monograph available for loan
    Monograph available for loan
    Ocean dynamics (2012)
    Berlin [u.a.] : Springer
    Details Availability
    Call number: AWI A6-12-0045
    Description / Table of Contents: Contents: - PART I FUNDAMENTAL LAWS. - 1 Preliminaries. - 2 Conservation laws for moving fluids. - PART II COMMON APPROXIMATIONS. - 3 Approximations derived from mode filtering. - 4 Approximations relating to density changes and geometric conditions. - 5 Geostrophic and quasi-geostrophic motions. - PART III OCEAN WAVES. - 6 Sound waves. - 7 Gravity waves. - 8 Long waves. - 9 Lagrangian theory of ocean waves. - 10 Forced waves. - PART IV OCEANIC TURBULENCE AND EDDIES. - 11 Small-scale turbulence. - 12 Geostrophic turbulence. - PART V ASPECTS OF OCEAN CIRCULATION THEORY. - 13 Forcing of the Ocean. - 14 The wind-driven circulation. - 15 The meridional overturning of the oceans. - 16 The circulation of the Southern Ocean. - PART VI APPENDIX. - A Mathematical basics. - B Models of the ocean circulation.
    Description / Table of Contents: Ocean Dynamics is a concise introduction to the fundamentals of fluid mechanics, non-equilibrium thermodynamics and the common approximations for geophysical fluid dynamics and presents a comprehensive approach to large-scale ocean circulation theory. Each of the five parts of the book - fundamental laws, common approximations, ocean waves, oceanic turbulence and eddies, and selected aspects of ocean circulation theory - starts with elementary considerations, blending then classical topics with more advanced developments of fluid mechanics and theoretical oceanography for the respective field.
    Type of Medium: Monograph available for loan
    Pages: xxiii, 704 S. : Ill., graph. Darst., Kt.
    Edition: 1. Aufl.
    ISBN: 9783642234491
    Branch Library: AWI Library
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  • 2
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    A wind-driven model of the ocean surface layer with wave radiation physics (2020)
    Springer Berlin Heidelberg
    Details
    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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  • 3
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    Contribution of oxygen minimum zone waters to the coastal upwelling off Mauritania (2009)
    Elsevier
    Details
    Publication Date: 2009-12-01
    Print ISSN: 0079-6611
    Electronic ISSN: 1873-4472
    Topics: Geosciences , Physics
    Published by Elsevier
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  • 4
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    Internal Gravity Wave Emission in Different Dynamical Regimes (2018)
    American Meteorological Society
    Details
    Publication Date: 2018-08-01
    Description: We aim to diagnose internal gravity waves emitted from balanced flow and investigate their role in the downscale transfer of energy. We use an idealized numerical model to simulate a range of baroclinically unstable flows to mimic dynamical regimes ranging from ageostrophic to quasigeostrophic flows. Wavelike signals present in the simulated flows, seen for instance in the vertical velocity, can be related to gravity wave activity identified by frequency and frequency–wavenumber spectra. To explicitly assign the energy contributions to the balanced and unbalanced (gravity) modes, we perform linear and nonlinear modal decomposition to decompose the full state variable into its balanced and unbalanced counterparts. The linear decomposition shows a reasonable separation of the slow and fast modes but is no longer valid when applied to a nonlinear system. To account for the nonlinearity in our system, we apply the normal mode initialization technique proposed by Machenhauer in 1977. Further, we assess the strength of the gravity wave activity and dissipation related to the decomposed modes for different dynamical regimes. We find that gravity wave emission becomes increasingly stronger going from quasigeostrophic to ageostrophic regime. The kinetic energy tied to the unbalanced mode scales close to Ro2 (or Ri−1), with Ro and Ri being the Rossby and Richardson numbers, respectively. Furthermore, internal gravity waves dissipate predominantly through small-scale dissipation, which emphasizes their role in the downscale energy transfer.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 5
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    The Total Energy Flux Leaving the Ocean’s Mixed Layer (2016)
    American Meteorological Society
    Details
    Publication Date: 2016-06-01
    Description: The total energy flux leaving the ocean’s spatially and seasonally varying mixed layer is estimated using a global ⅝1/10° ocean general circulation model. From the total wind-power input of 3.33 TW into near-inertial waves (0.35 TW), subinertial fluctuations (0.87 TW), and the time-mean circulation (2.11 TW), 0.92 TW leave the mixed layer, with 0.04 TW (11.4%) due to near-inertial motions, 0.07 TW (8.04%) due to subinertial fluctuations, and 0.81 TW (38.4%) due to time-mean motions. Of the 0.81 TW from the time-mean motions, 0.5 TW result from the projection of the horizontal flux onto the sloped bottom of the mixed layer. This projection is negligible for the transient fluxes. The spatial structure of the vertical flux is determined principally by the wind stress curl. The mean and subinertial fluxes leaving the mixed layer are approximately 40%–50% smaller than the respective fluxes across the Ekman layer according to the method proposed by Stern. The fraction related to transient fluctuations tends to decrease with increasing depth of the mixed layer and with increasing strength of wind stress variability.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 6
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    Revisiting the Generation of Internal Waves by Resonant Interaction with Surface Waves (2016)
    American Meteorological Society
    Details
    Publication Date: 2016-07-25
    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 10−3 TW in total, based on a realistic wind-sea spectrum (depending on wind speed), mixed layer depths, and stratification below the mixed layer taken from a state-of-the-art numerical ocean model. Unlike previous calculations of 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 dissipation 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 interaction 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 10 m s−1.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 7
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    Evaluating the Global Internal Wave Model IDEMIX Using Finestructure Methods (2017)
    American Meteorological Society
    Details
    Publication Date: 2017-09-01
    Description: Small-scale turbulent mixing affects large-scale ocean processes such as the global overturning circulation but remains unresolved in 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, Energy and Mixing (IDEMIX) predicts the internal wave energy, dissipation rates, and diapycnal 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 reproduces the magnitude and the large-scale variations of the Argo-derived dissipation rate and energy level 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 additional physical detail and by better constraining the processes already included in the model. A prominent 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.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 8
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    A Closure for Internal Wave–Mean Flow Interaction. Part I: Energy Conversion (2017)
    American Meteorological Society
    Details
    Publication Date: 2017-06-01
    Description: When internal (inertia-)gravity waves propagate in a vertically sheared geostrophic (eddying or mean) flow, they exchange energy with the flow. A novel concept parameterizing internal wave–mean flow interaction in ocean circulation models is demonstrated, based on the description of the entire wave field by the wave-energy density in physical and wavenumber space and its prognostic computation by the radiative transfer equation. The concept enables a simplification of the radiative transfer equation with a small number of reasonable assumptions and a derivation of simple but consistent parameterizations in terms of spectrally integrated energy compartments that are used as prognostic model variables. The effect of the waves on the mean flow in this paradigm is in accordance with the nonacceleration theorem: only in the presence of dissipation do waves globally exchange energy with the mean flow in the time mean. The exchange can have either direction. These basic features of wave–mean flow interaction are theoretically derived in a Wentzel–Kramers–Brillouin (WKB) approximation of the wave dynamics and confirmed in a suite of numerical experiments with unidirectional shear flow.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 9
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    A Closure for Internal Wave–Mean Flow Interaction. Part II: Wave Drag (2017)
    American Meteorological Society
    Details
    Publication Date: 2017-06-01
    Description: A novel concept for parameterizing internal wave–mean flow interaction in ocean circulation models is extended to an arbitrary two-dimensional flow with vertical shear. The concept is based on the description of the entire wave field by the wave-energy density in physical and wavenumber space and its prognostic computation by the radiative transfer equation integrated in wavenumber space. Energy compartments result for the horizontal direction of wave propagation as additional prognostic model variables, of which only four are taken here for simplicity. The mean flow is interpreted as residual velocities with respect to the wave activity. The effect of wave drag and energy exchange due to the vertical shear of the residual mean flow is then given simply by a vertical flux of momentum. This flux is related to the asymmetries in upward, downward, alongflow, and counterflow wave propagation described by the energy compartments. A numerical implementation in a realistic eddying ocean model shows that the wave drag effect is a significant sink of kinetic energy in the interior ocean.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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  • 10
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    Mixed Rossby–Gravity Wave–Wave Interactions (2019)
    American Meteorological Society
    Details
    Publication Date: 2019-01-01
    Description: Mixed triad wave–wave interactions between Rossby and gravity waves are analytically derived using the kinetic equation for models of different complexity. Two examples are considered: initially vanishing linear gravity wave energy in the presence of a fully developed Rossby wave field and the reversed case of initially vanishing linear Rossby wave energy in the presence of a realistic gravity wave field. The kinetic equation in both cases is numerically evaluated, for which energy is conserved within numerical precision. The results are validated by a corresponding ensemble of numerical model simulations supporting the validity of the weak-interaction assumption necessary to derive the kinetic equation. Since they are generated by nonresonant interactions only, the energy transfers toward the respective linear wave mode with vanishing energy are small in both cases. The total generation of energy of the linear gravity wave mode in the first case scales to leading order as the square of the Rossby number in agreement with independent estimates from laboratory experiments, although a part of the linear gravity wave mode is slaved to the Rossby wave mode without wavelike temporal behavior.
    Print ISSN: 0022-3670
    Electronic ISSN: 1520-0485
    Topics: Geosciences , Physics
    Published by American Meteorological Society
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