Thèse Modélisation des Marées Internes dans les Océans du Globe - Focus sur la Région Arctique H/F - Doctorat.Gouv.Fr

Établissement : Institut National Polytechnique de Toulouse École doctorale : SDU2E - Sciences de l'Univers, de l'Environnement et de l'Espace Laboratoire de recherche : IMFT - Institut de Mécanique des Fluides de Toulouse Direction de la thèse : Matthieu MERCIER ORCID 0000000199653316 Début de la thèse : 2027-09-01 Date limite de candidature : 2026-11-23T23:59:59 L'objectif principal de ce projet est de développer une méthode numérique performante pour évaluer les ondes internes générées dans les océans du globe. Basée sur des modélisations développées récemment au sein de l'IMFT, cette méthode permettra de calculer l'écoulement ainsi que l'énergie rayonnée par les ondes internes issues du forçage de marée. Ces ondes appelées 'marées internes', représentent une part considérable de l'énergie nécessaire pour mélanger en profondeur les océans. Cette méthode proposera une approche alternative à la modélisation numérique directe des ondes internes pour des fonds océaniques à haute résolution, qui reste inaccessible à ce jour du fait des échelles spatio-temporelles des ondes internes.

Une évaluation réaliste de la génération des marées internes est cruciale pour paramétrer correctement le mélange induit par les ondes dans les modèles climatiques. Au cours du projet, un intérêt particulier sera porté à l'Océan Arctique qui est en plein réchauffement. Les conditions océaniques y évoluent rapidement et à mesure que la banquise fond, les ondes internes pourraient s'intensifier, rendant la précision des paramétrages du mélange océanique qu'elles induisent particulièrement important.
Oceanic internal waves are fluid oscillations of particular importance to the dynamics of the oceans. They are generated by steady currents over the ocean floor [10], by oscillating flows (tides) around submarine topography [9], or by winds at the surface [6]. With wavelengths on the order of 100 km, these waves propagate over thousands of kilometers [1] and are associated with significant vertical displacements [12]. Once generated, internal waves constitute a major energy source contributing to deep branches of the global oceanic circulation [22]. Hence, accurately accounting for these waves is also a key challenge for climate change modeling [15,P1].

Observing internal waves on a global scale is particularly difficult, as they occur in the ocean depths and only induce centimeter-scale surface displacements [20]. However, recent decades have seen advances in satellite altimetry that allow for the use of long-term records with increasingly high horizontal resolution [24,25] (about 1 km for the new SWOT satellite). Direct field observations are limited to specific locations with high internal wave activity, such as Hawaii [21], making detailed analysis over large areas difficult. To interpret these observations, internal wave dynamics are reproduced through regional [7, 17, 23] or even global [2] numerical simulations, albeit at considerable computational cost.

To address this cost, the analytical modeling of wave generation by oscillatory flow over ocean topography has been the subject of numerous studies-mostly two-dimensional and subject to certain analytical constraints [3-6, 11, 14]-that only allow for specific types of topography (e.g., solely gentle or steep slopes, low height relative to ocean depth, or periodic vs. isolated features). Two recent methods developed by the supervising team have overcome many of these limitations: one relies on a 3D immersed-boundary approach, enabling prediction of internal waves around a topographic feature of arbitrary shape and height, provided it is isolated [LD1]; the other allows for the treatment of any type of topographic profile, including continental slopes [PA1].

Applying these new methods to specific ocean regions, or even at a global scale, could yield more reliable estimates of energy conversion from surface tides to internal waves than earlier methods [8, 13, 16, 18], which could not incorporate realistic topography. A realistic assessment of the internal tide generation is crucial for the realistic parameterization of wave-driven mixing in climate models [P1], where this small-scale process affects large-scale dynamics [15] but cannot be resolved directly. An area of particular interest is the Arctic Ocean, where the accuracy of such mixing parameterizations will become substantially more relevant in the future as sea ice continues to melt and internal waves could become stronger [19]. Model internal tides in the global ocean using realistic bathymetry, tidal, and stratification data.
Estimate energy dissipation in the oceans associated with internal tide generation at the ocean-basin or even global scale.
Characterize oceanic internal tides in the Arctic Ocean under various climate scenarios. The primary objective is to employ recent semi-analytical methods (involving the numerical solution of a system of coupled equations) to model internal wave generation in specific oceanic regions. These semi-analytical approaches were developed by M. Mercier's team [PA1, LD1] in collaboration with N. Grisouard (University of Toronto). They will be applied to realistic configurations, using seafloor topography maps as well as geophysical data on stratification and surface tidal flows as model inputs.

Numerical developments are required to scale up realistic internal tide modeling from isolated topographic features to the scale of ocean basins or even the entire globe. The successful candidate will benefit from the expertise of F. Pollmann, who previously conducted global estimates using other analytical methods [P2], and works on implementing these in energy constrained parameterizations of internal-wave driven mixing for the improvement of climate models.

Model validation will involve comparisons with various datasets: regional numerical simulations of the Arctic region performed by F. Pollmann's team, and publicly available data derived from satellite altimetry analysis [24, 25].

Master 2 - Plusieurs profils peuvent convenir à ce projet ; la personne pourra avoir une expérience avancée en mécanique des fluides, physique, géophysique, mathématiques appliquées, etc. Mais des bases solides en méthodes mathématiques appliquées à la Physique ou à la Géophysique sont attendues, ainsi que des compétences en méthodes numériques.

Application link : https://edd-projets.utoulouse.fr/