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Modélisation numérique de la marée interne : Contrôles hydrauliques et topographiques

Abstract : Internal tides are involved in the Meridional Overturning Circulation energy balance. The issue about the relative importance of the mechanical and thermodynamical energy sources induces a need for a quantitative evaluation of the energy transfers and for a clear understanding of the physical processes involved in these energy transfers. In supercritical regions such as the strait of Gibraltar or the Hawaiian Ridge, large topography variations and strong currents lead to more complex generation mechanisms of internal waves and environmental interactions. They can be subject locally to spectacular breaking, with turbulent structures observed hundreds of meters above the seafloor, and driving turbulence orders of magnitude higher than open-ocean levels. These regions are also effective at generating nonlinear internal waves (ISWs) which persist for days after their generation and are suspected to be responsible for important remote energy transfers. In these “extreme” regions, ISWs dynamics is also more difficult to model. These situations are highly non-hydrostatic and non-linear with strong instabilities, strong velocity and density gradients and steep slopes. Moreover, in these regions, actual internal wave’s parameterizations are often inadequate. So there is a real need to understand and represent better the ISWs dynamic in these areas. This thesis follows the line of research of Dossmann (2012), on topographically induced internal solitary waves which used a complementary approach relying on numerical and experimental configurations at laboratory scale. In this context, we continue to explore internal tide regimes but in “supercritical” regions: internal tide generation area with supercritical topography and hydraulic control. Simulations are performed using the nonhydrostatic and non-Boussinesq version of the regional oceanic circulation model SNH. In a first part, taking an idealized modeling approach at laboratory scale, we examined a range of different internal waves regimes in “supercritical” regions. Relying on quasi-direct numerical simulations (quasi-DNS), a regime analysis has been proposed using and identifying key non-dimensional parameters for ISWs dynamics. This analysis has permitted to recover a topographic control on vertical mode generation characterized by the ratio of vertical mode wavelength to topography width, even above supercritical topography. The topographic selection criterion has proven to be a useful indicator of high mode solitary wave formation in non-linear regime. The purpose of the second part is to extend the previous studies at laboratory scales towards more realistic oceanic conditions. In this regard, the regime analysis is applied to a idealized large scale oceanic strait through a similitude principle. The idealized strait configuration succeeds in representing laboratory scale strait regime at largest and realistic scales. Then our analysis is applied to two well-known realistic cases: the Strait of Gibraltar and Georges Bank through large eddy simulations. These two oceanographic “supercritical” regions are particularly interesting for their specific topography and stratification conditions.
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Lucie Bordois. Modélisation numérique de la marée interne : Contrôles hydrauliques et topographiques. Océanographie. Universite Toulouse III Paul Sabatier, 2015. Français. ⟨tel-01281760⟩

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