Wave-induced boundary mixing in a partially mixed estuary

We present observations that reveal the existence of horizontally propagating, tidally-driven, high-frequency internal wave (IW) packets in a channel of the partially mixed St. Lawrence Estuary. The packets propagate transversely to the channel axis and collide with the shoaling lateral boundaries. The structure and energy of IWs are diagnosed with a two-dimensional, nonlinear nonhydrostatic model, and the results are compared with weakly nonlinear Korteweg-de-Vries (KdV) theory. The behavior of IWs running into the shoaling lateral boundary is examined in terms of published laboratory and numerical experiments. Our analysis indicates that IWs break on the slope, during which 6% of their energy is converted into potential energy through vertical mixing. The corresponding buoyancy flux, when averaged over the surf zone and the time of the mixing event, is more than an order of magnitude larger than values predicted by a published non-IWresolving three-dimensional (3D) baroclinic circulation model of the region. Even averaging across the full domain and tidal period yields mixing rates that are a significant proportion of those in the 3D circulation model. These indirect inferences suggest that wave-induced boundary mixing may be of general significance in partially mixed estuaries

Le livre numérique québécois en bibliothèque : libérez le trésor

Cet article examine le modèle de gestion numérique des droits (GND) de la plateforme québécoise de livres numériques PretNumerique.ca, notamment en le comparant à d'autres modèles (musique, films, livres numériques ailleurs dans le monde)

Interfacial solitary wave run-up in the St. Lawrence Estuary

Density variations show evidence of interfacial solitary waves (ISW) running up the sloping boundary of an island in the St. Lawrence Estuary, confirming inferences based remote sensing. Further detail is suggested by simulations created with a two-dimensional nonhydrostatic numerical model. The simulations confirm theoretical predictions of the location of wave breaking, something that is difficult to observe in the field. Two other results of the simulations match laboratory findings: the creation of turbulent boluses that propagate upslope of the breaking zone, and the creation of an intermediate layer that transports mixed water away from the mixing site. Although our sampling could not resolve the intermediate mixing layer, it did provide evidence of boluses. In addition to ISW breaking the bolus and intrusion effects may also be important in coastal regions

Generation of internal solitary waves by frontally forced intrusions in geophysical flows

International audienceInternal solitary waves are hump-shaped, large-amplitude waves that are physically analogous to surface waves except that they propagate within the fluid, along density steps that typically characterize the layered vertical structure of lakes, oceans and the atmosphere. As do surface waves, internal solitary waves may overturn and break, and the process is thought to provide a globally significant source of turbulent mixing and energy dissipation. Although commonly observed in geophysical fluids, the origins of internal solitary waves remain unclear. Here we report a rarely observed natural case of the birth of internal solitary waves from a frontally forced interfacial gravity current intruding into a two-layer and vertically sheared background environment. The results of the analysis carried out suggest that fronts may represent additional and unexpected sources of internal solitary waves in regions of lakes, oceans and atmospheres that are dynamically similar to the situation examined here in the Saguenay Fjord, Canada

Turbulence and boluses on an internal beach

In a manner similar to that of surface waves on beaches, high-frequency interfacial waves (IWs) may break when approaching the \u27internal coastline,\u27 where the undisturbed pycnocline intersects the shoaling bottom. This process has been studied previously in idealized laboratory and numerical experiments but there are few field observations to document the properties of IWs shoaling on natural internal beaches. This paper presents observations of currents, density and turbulence collected inshore of the break point of an internal beach of the St. Lawrence Estuary. A series of large- and small-amplitude complex-shaped and unorganized internal boluses was observed. The structure of these boluses is discussed, along with their role in boundary turbulence and transport

Sediment resuspension and nepheloid layers induced by long internal solitary waves shoaling orthogonally on uniform slopes

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Continental Shelf Research 72 (2014): 21-33, doi:10.1016/j.csr.2013.10.019.Two-dimensional, nonlinear and nonhydrostatic field-scale numerical simulations are used to examine the resuspension, dispersal and transport of mud-like sediment caused by the shoaling and breaking of long internal solitary waves on uniform slopes. The patterns of erosion and transport are both examined, in a series of test cases with varying conditions. Shoreward sediment movement is mainly within boluses, while seaward movement is within intermediate nepheloid layers. Several relationships between properties of the suspended sediment and control parameters are determined such as the horizontal extent of the nehpeloid layers, the total mass of resuspended sediment and the point of maximum bed erosion. The numerical results provide a plausible explanation for acoustic backscatter patterns observed during and after the shoaling of internal solitary wavetrains in a natural coastal environment. The results may further help interpret sedimentary structures that may have been shaped by internal waves and add an another e ective mechanism for o shore dispersal of muddy sediments.This research was funded by the Natural Sciences and Engineering Research Council of Canada (D. Bourgault) and by the Spanish Research Project CGL2009-13254 (M. Morsilli)

Magnetic Texturing of High-Tc Superconductors

International audienc

Measurements of shoaling internal waves and turbulence in an estuary

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 118 (2013): 273–286, doi:10.1029/2012JC008154.The shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas. Including such effects in numerical models demands improvements in the understanding of several aspects of the energetics, especially those relating to turbulence generation, and observations are needed to build this understanding. To address some of these issues in the estuarine context, we undertook an intensive field program for 10 days in the summer of 2008 in the St. Lawrence Estuary. The sampling involved shore-based photogrammetry, ship-based surveys, and an array of moorings in the shoaling region that held both conventional and turbulence-resolving sensors. The measurements shed light on many aspects of the wave shoaling process. Wave arrivals were generally phase-locked with the M2 tide, providing hints about far-field forcing. In the deeper part of the study domain, the waves propagated according to the predictions of linear theory. In intermediate-depth waters, the waves traversed the field site perpendicularly to isobaths, a pattern that continued as the waves transformed nonlinearly. Acoustic Doppler velocimeters permitted inference of the turbulent energetics, and two main features were studied. First, during a period of shoaling internal waves, turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude. Second, the evolving spectral signatures associated with a particular wave-shoaling event suggest that the turbulence is at least partly locally generated. Overall, the results of this study suggest that parameterizations of wave-induced mixing could employ relatively simple dynamics in deep water, but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions.The work was supported by the Killam Foundation, the Natural Sciences and Engineering Research Council of Canada, the Canadian Foundation for Innovation, the Canadian Foundation for Climate and Atmospheric Sciences, and the Canadian Department of Fisheries and Oceans.2013-07-3

Ni-Mn-Ga films in the austenite and the martensite structures at room temperature: Uniaxial texturation and epitaxial growth

Ni-Mn-Ga films in the austenite and the martensite structures at room temperature have been obtained using the DC magnetron sputtering technique. Two elaboration processes were studied. A first batch of samples was deposited using a resist sacrificial layer in order to release the film from the substrate before vacuum annealing. This process leads to polycrystalline films with a strong (022) fiber texture. The martensitic phase transformation of such polycrystalline freestanding films has been studied by optical and scanning electron microscopy. A second batch of samples was grown epitaxially on (100)MgO substrates using different deposition temperatures. The texture has been analyzed with four-circle X-ray diffraction. Epitaxial films crystallized both in the austenite and the martensite structures at room temperature have been studied

Martensite structures and twinning in substrate-constrained epitaxial Ni-Mn-Ga films deposited by a magnetron co-sputtering process

In order to obtain Ni-Mn-Ga epitaxial films crystallized in martensite structures showing Magnetic-Induced Rearrangement (MIR) of martensite variants, a fine control of the composition is required. Here we present how the co-sputtering process might be helpful in the development of Ni-Mn-Ga epitaxial films. A batch of epitaxial Ni-Mn-Ga films deposited by co-sputtering of a Ni-Mn-Ga ternary target and a pure manganese target has been studied. The co-sputtering process allows a precise control of the film compositions and enables keeping the epitaxial growth of Ni-Mn-Ga austenite during deposition at high temperature. It gives rise to tune the content of the MIR-active 14-modulated martensite in the film at room temperature, as well as micro and macro-twinned domains sizes