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  • 1
    Electronic Resource
    Electronic Resource
    Breaking and cascade of internal gravity waves in a continuously stratified fluid (1993)
    Springer
    Flow, turbulence and combustion 51 (1993), S. 305-311 
    Details
    ISSN: 1573-1987
    Keywords: internal waves ; parametric instability ; wavebreaking ; mixing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The evolution of a few large scale high frequency standing internal waves confined to a vertical plane is studied numerically. The growth of nonlinear interactions leads to a transfer of energy toward small vertical scales and lower frequencies: the result is a steep energy decrease due to wave breaking. Induced mixing is evaluated. A parametric forcing is also introduced in order to compare with laboratory experiments. Wave breaking also occurs but as opposed to the unforced case different phases are next observed: internal wave growth due to constructive forcing alternate with energy decrease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01082553
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    Paper (German National Licenses)
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  • 2
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    Tropical storm-induced near-inertial internal waves during the Cirene experiment: energy fluxes and impact on vertical mixing (2013)
    Wiley
    Details
    Publication Date: 2013-01-18
    Description: [1]  Near-inertial Internal Waves (NIW) excited by storms and cyclones play an essential role in driving turbulent mixing in the thermocline and interior ocean. Storm-induced mixing may be climatically relevant in regions like the thermocline ridge in the southwestern Indian Ocean, where a shallow thermocline and strong high frequency wind activity enhance the impact of internal gravity wave-induced mixing on sea surface temperature. The Cirene research cruise in early 2007 collected ship-borne and mooring vertical profiles in this region under the effect of a developing tropical cyclone. In this paper, we characterize the NIW field and the impact of these waves on turbulent mixing in the upper ocean. NIW packets were identified down to 1000 m, the maximum depth of the measurements. We estimated a NIW vertical energy flux of up to 2.5 mW m −2 within the pycnocline, which represents about 10% of the maximum local wind power input. A non-negligible fraction of the wind power input is hence potentially available for subsurface mixing. The impact of mixing by internal waves on the upper ocean heat budget was estimated from a fine-scale mixing parameterization. During the first leg of the cruise (characterized by little NIW activity), the average heating rate due to mixing was ~0.06°C month −1 in the thermocline (23–24 kg m −3 isopycnals). During the second leg, characterized by strong NIW energy in the thermocline and below, this heating rate increased to 0.42°C month −1 , indicative of increased shear instability along near inertial wave energy pathways.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Full-depth desalination of warm sea ice (2013)
    Wiley
    Details
    Publication Date: 2013-02-02
    Description: [1]  The large-scale Arctic sea-ice retreat induces a gradual replacement of thick, multi-year sea ice by thinner first-year ice. The latter has distinctive physical properties and is in particular substantially saltier. It is generally thought that while salt rejection occurs primarily during ice formation in winter, most of the remaining brine is flushed out of the ice by the percolating surface melt water in summer. Here, it is argued that a substantial part of this residual desalination of first-year sea ice can occur well before summer melt, due to brine convection over the full thickness of the ice, once the ice temperature is higher than a threshold that depends on bulk salinity and thickness. This critical temperature is substantially higher than the permeability threshold. The argument stems from a theoretical analysis of the porous Rayleigh number depicting the propensity for convection in the mushy-layer theory. It is supported by simulations performed with a state-of-the-art 1-D sea-ice model. The study was initially motivated by observations collected in March 2007 in Storfjorden, Svalbard. Those are indirect, however, and are thus presented here as a possible example. Two sporadic anomalies of seawater salinity were recorded close to the base of 40 cm thick ice in temperature conditions that are incompatible with ice formation. Analyses and simulations forced with observed atmospheric conditions suggest that the second peak is caused by flushing of meltwater, while the first and most intense peak is likely associated with an episode of brine convection over the full depth of the ice, yielding significant desalination.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 4
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    Internal waves and vertical mixing in the Storfjorden Polynya, Svalbard (2011)
    Wiley
    Details
    Publication Date: 2011-12-24
    Description: Latent heat polynya are preferential sites for dense water formation through brine release. The combined action of winds and heat loss leading to sea ice fracture followed by the reactivation of sea ice formation drives this process of dense water formation. The impact of high-frequency dynamics, and especially internal wave breaking, on this process is investigated here, with the analysis of hydrographic observations collected from a drifting mooring in Storfjorden, Svalbard. The main frequency components of the barotropic tide are first revealed by the analysis of a 23-day time series of pressure data. Interestingly the same frequency peaks are isolated by a spectral analysis of isopycnal displacements, suggesting a tidal forcing for these baroclinic waves. The hypothesis of local generation in the Storfjorden is next examined and numerous sites of potential generation are identified specifically for semi-diurnal and sixth-diurnal frequencies. Diurnal baroclinic waves, however, do not appear to be locally generated, but rather popagate cyclonically along the shelf as internal Kelvin waves. The characteristic of these waves and their energy flux are then inferred. A parameterization of dissipation based on the potential energy of the internal wavefield is next proposed and an upper bound for dissipation rate within overturning regions is provided. The most vigorous mixing is associated with brine release events (i.e. strong vertical mixing through thermohaline convection) with eddy diffusivities of up to 10−3 m2 s−1. The background mixing (likely associated with internal wave breaking), however, displays values within [10−6, 10−4] m2 s−1. This background mixing contributes about O(0.1) W m−2 to the vertical heat flux with a net heating in the bottom layer and cooling in the upper layer. Local heating and cooling rates of the order of 0.025°C month−1 are obtained which is significant with respect to the 0.1°C temperature difference between the bottom and surface layers.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 5
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    On the physical and biogeochemical processes driving the high-frequency variability of CO2 fugacity at 6°S, 10°W: Potential role of the internal waves (2014)
    Wiley
    Details
    Publication Date: 2014-11-09
    Description: The availability of nutrients in the mixed layer is the main limitation to organic carbon biological production in the tropical regions. In this paper, we investigate the potential role of internal waves at promoting the development of biological activity on a PIRATA mooring at 6°S, 10°W. This mooring is located above the Mid-Atlantic Ridge where we observe strong internal waves. Using a one dimensional physical and biogeochemical coupled model, we simulate dissolved inorganic carbon (DIC). Providing the influence of vertical advection and turbulent diapycnal diffusivity are accounted for, we find that this model provides a good fit with observed in-situ CO 2 fugacity (fCO 2 ). Main effect of internal waves is to rapidly increase the DIC, thus the fCO 2 and the nutrients in the mixed layer. The latter induce progressive development of biological activity leading to gradual DIC decrease. Our study highlights the importance of correctly taking into account the effect of internal waves in tropical regions.
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    Topics: Geosciences , Physics
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  • 6
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    Ice production in Storfjorden (Svalbard) estimated from a model based on AMSR-E observations: impact on water mass properties (2013)
    Wiley
    Details
    Publication Date: 2013-11-30
    Description: Storfjorden, which hosts a latent heat polynya, is a well known region of dense water formation. This Brine-enriched Shelf Water (BSW) displays substantial year to year variability in its properties, which is partly linked to interannual variations in ice production. Here we have developed a model based on high-resolution AMSR-E satellite sea-ice concentration data, available between 2002 and 2011, and atmospheric forcing to estimate the ice production in the polynya and associated salt release. The average modeled ice production for the epoch 2002-2011 is 47 km 3 per year, corresponding to a salt release of 1200×10 9 kg. The two most anomalous winters were 2004-2005 (salt deficit of -367×10 9 kg) and 2007-2008 (salt excess of 398×10 9 kg). Available observations of BSW properties are relatively scarce during this period and are here augmented with data collected in March 2007 from an ice-tethered mooring to the northwest of the fjord. BSW was found up to the surface, with maximum salinity and density of 35.27 and 28.4 kg m -3 , respectively, at 55 m. In addition supercooled water was found down to 10 m under relatively mild atmospheric conditions. It is shown to have formed a week before, during an intense frazil ice formation episode, exceeding 2 km 3 of frazil ice according to the model. Although observations remain too few to robustly assess the relation between ice production and BSW properties, there is suggestion of a direct impact for most anomalous years. The exceptional ice production in 2007-2008 is most likely the cause of the very saline BSW in 2008 and strong plume of dense water towards Fram Strait reported by other authors. Anomalous ice production appears predominantly driven by the duration of the freezing season and anomalous opening of the polynya.
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    Topics: Geosciences , Physics
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  • 7
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    How important are diapycnal mixing and geothermal heating for the deep circulation of the Western Mediterranean? (2017)
    Wiley
    Details
    Publication Date: 2017-07-09
    Description: The dissipation rate of turbulent kinetic energy ε and the associated diapycnal turbulent mixing is inferred from a set of microstructure observations collected over several cruises from year 2012 to 2014. The geographical distribution of ε highlights several regions of enhanced levels of turbulence ranging from 10 -9 to 10 -6 W kg -1 : the Sicily Channel, the Corsica Channel and the Ligurian Sea. Elsewhere, ε was small, often below 10 -10 W kg -1 . Below 1300m, geothermal heating provides three-fold more buoyancy than small scale turbulence. Geothermal heating and turbulent diffusion provide enough buoyancy to balance 15% to 50% of a mean yearly deep water formation rate of 0.9 to 0.3 Sv, respectively. The remaining part has to eventually overflow through the Strait of Gibraltar.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 8
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    Nonhydrostatic Simulations of Tide-Induced Mixing in the Halmahera Sea: A Possible Role in the Transformation of the Indonesian Throughflow Waters (2017)
    Wiley
    Details
    Publication Date: 2017-10-11
    Description: The Indonesian Throughflow (ITF) waters are significantly transformed within the Indonesian Archipelago and consequently influence the large-scale ocean circulation such as Agulhas and Leeuwin Currents. Existing ocean general circulation models (OGCMs) are, however, incapable of reproducing the transformation of the ITF waters, since tidal forcing is neglected in such models. In the present study, we first conduct high-resolution non-hydrostatic three-dimensional numerical experiments focusing on the transformation of the ITF waters in the Halmahera Sea which is thought to be the most important bottleneck in simulating the ITF water-mass properties. It is shown that intensive vertical mixing induced by breaking of internal tides in the shallow regions in the Halmahera Sea dilutes the ITF waters, significantly reducing model biases found in the existing OGCMs. We next evaluate quantitatively the effect of tide-induced vertical mixing on the transformation of the ITF waters. It is shown that tide-induced vertical mixing dominates the transformation of the ITF waters, although some supplementary processes such as horizontal mixing associated with the sub-mesoscale eddies resulting from tidal interaction with land configurations cannot be ignored.
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    Topics: Geosciences , Physics
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  • 9
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    Large amplitude internal tides, solitary waves and turbulence in the central Bay of Biscay (2013)
    Wiley
    Details
    Publication Date: 2013-05-08
    Description: [1]  Microstructure and fine-scale measurements collected in the central Bay of Biscay during the MOUTON experiment are analyzed to investigate the dynamics of internal waves and associated mixing. Large amplitude internal tides (ITs), that excite internal solitary waves (ISWs) in the thermocline, are observed. ITs are dominated by modes 3 and 4, while ISWs projects on mode-1 that is trapped in the thermocline. Therein, ITs generate a persistent narrow shear band, which is strongly correlated with the enhanced dissipation rate in the thermocline. This strong dissipation rate is further reinforced in presence of ISWs. Dissipation rates during the period without ISWs largely agree with the MacKinnon-Gregg scaling proposed for internal wave fields dominated by a low frequency mode, while they show poor agreement with the Gregg-Henyey parameterization valid for internal wave fields close to the GM model. The agreement with the MacKinnon-Gregg scaling is consistent with the fact that turbulent mixing is here driven by the low-frequency internal tidal shear.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 10
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    Generation and propagation of internal tides and solitary waves at the shelf edge of the Bay of Biscay (2015)
    Wiley
    Details
    Publication Date: 2015-09-08
    Description: High frequency mooring data were collected near the northern shelf edge of the Bay of Biscay to investigate the generation and propagation of internal tides and internal solitary waves (ISWs). During spring tide, strong nonlinear internal tides and large amplitude ISWs are observed every semi-diurnal tidal period. While onshore propagation was expected since the mooring is located shoreward of the maximum internal tidal generation location, both onshore and seaward traveling internal tides are identified. Within a tidal period at spring tide, three ISW packets are observed. Like internal tides, different ISW packets have opposite (seaward and shoreward) propagating direction. Based on realistic hydrostatic HYCOM simulations, it is suggested that advection by the barotropic tide affects wave generation and propagation significantly and is essential for the seaward traveling internal tides to appear shoreward of their generation location. A two-layer idealized non-hydrostatic model derived by Gerkema [1996] further confirms the effect of advection on the generation and propagation of internal tides. Moreover, the two-layer model reproduces one seaward propagating ISW packet and one shoreward propagating ISW packet, indicating that the offshore and onshore traveling ISWs are excited by nonlinear steepening of the seaward and shoreward traveling internal tides, respectively. This article is protected by copyright. All rights reserved.
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    Topics: Geosciences , Physics
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