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Transport atmosphérique et ondes dans les atmosphères en superrotation

Abstract : This study deals with the understanding of the superrotation dynamical mecanism which takes place in the atmospheres of Venus and Titan (Saturn's satellite). It is caracterised by a faster rotation of the atmosphere compared with the rotation of the "planet". This dynamical phenomenon, peculiar to slow rotating "telluric bodies", is a preferential subject to study atmospheric transport mecanisms. The goal is to understand and to constrain dynamical processes which maintain superrotation by studying particularly the transport of angular momentum (and tracers) by the mean meridional circulation and waves. The study uses the 2D-Circulation Model of Titan (coupled dynamical-chemical-microphysical model), and the 3D General Circulation Model (GCM) of Vénus, under development in the Laboratory of Dynamic Meteorology (LMD). Recent results given by Cassini-Huygens and Venus Express space missions have been used for the validation of modelised dynamical mecanisms.

First, I have validated the meridional criculation in Titan model, by comparison between observations and modelised chemical distributions, for which dynamical transport has a key role. This meridional circulation allows to validate dynamical mecanisms responsible for the superrotation in the model, and to interpret observations in terms of thermal, dynamical and chemical structures.

Moreover, analysis tools that I have developped for the Venus GCM allow, firstly to describe transport mecanisms (of angular momentum and passive tracers) by mean meridional circulation and waves, and secontly to give the mean caracteristics of waves (Eliassen Palm diagnostics, spectral analysis, etc.). Thanks to these tools, my PhD study shows that the modelised mean meridional circulation transport angular momentum upward in equatorial regions and poleward in the upper branch of the Hadley cells. Barotropic instabilities in high latitudes interact with the global mean flow that creates planetary scale waves which bring back angular momentum to the equator. In the model, it is the high frequency waves, and in particular the famous 4-5 terrestrial earth period waves observed in Venus clouds, that mostly contribute to the latitudinal transport, thus allowing to maintain the equatorial superrotation in the model.
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https://pastel.archives-ouvertes.fr/tel-00410181
Contributor : Audrey Crespin <>
Submitted on : Tuesday, August 18, 2009 - 12:12:52 PM
Last modification on : Tuesday, October 20, 2020 - 10:53:54 AM
Long-term archiving on: : Tuesday, June 15, 2010 - 10:32:44 PM

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  • HAL Id : tel-00410181, version 1

Citation

Audrey Crespin. Transport atmosphérique et ondes dans les atmosphères en superrotation. Physique [physics]. Ecole Polytechnique X, 2008. Français. ⟨tel-00410181⟩

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