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Dynamique et Modélisation des Atmosphères Profondes : Application à l'Atmosphère de Titan

Abstract : Large-scale atmospheric and oceanic motions are fairly well described under the so-called shallow-atmosphere approximation, which neglects the thickness of the atmosphere comparing to the planetary radius. Titan is the biggest moon of Saturn and has a thick atmosphere with an aspect ratio reaching almost 25%. It is then preferable not to make the shallow-atmosphere approximation to model its atmospheric general circulation. This thesis solves problems in modeling of such deep-atmospheres and addresses some issues for understanding their dynamics. The shallow-atmosphere and traditional approximation neglecting the part of the Coriolis force due to the horizontal component of the planetary rotation rate vector (also called as non-traditional part) seem to be inseparable to satisfy the conservation of absolute angular momentum. However, we show that it is possible to retain non-traditional terms under the shallow-atmosphere approximation while satisfying all conservation laws, in the compressible Euler equations as well as in the shallow-water equations on the rotating sphere. In most cases, given the small aspect ratio, this new non-traditional model is accurate. In this case, several idealized zonal jet stability and free evolving turbulence studies have been conducted using shallow-water and Boussinesq models taking into account the complete Coriolis force. We highlight the parameters for which the non-traditional effects are significant and discuss the dynamical effects in realistic cases. To model general circulation of Titan's atmosphere, we integrate the quasi-hydrostatic equations in the dynamical core of the LMD-Z (Titan) atmospheric general circulation model. After identifying the Hamiltonian structure of the equations, we imitate the formulation at discrete level to conserve total energy. Various test cases are performed in order to validate the stability and the accuracy of the new dynamical core. The latter is applied to Titan's atmosphere. Firstly, an idealized simulation is performed starting from an atmosphere at rest and using a Newtonian relaxation. Then more realistic simulations are implemented using parameterizations of LMD-Z (Titan).
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Contributor : Marine Tort Connect in order to contact the contributor
Submitted on : Tuesday, March 31, 2015 - 3:29:54 PM
Last modification on : Thursday, March 17, 2022 - 10:08:18 AM


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  • HAL Id : tel-01137840, version 1


Marine Tort. Dynamique et Modélisation des Atmosphères Profondes : Application à l'Atmosphère de Titan. Sciences de l'environnement. Ecole Polytechnique, 2015. Français. ⟨NNT : ⟩. ⟨tel-01137840⟩



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