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PhD Defense

Maxence LEFEVRE (LMD)

Title : Modélisation petite échelle de l’atmosphère de Vénus : Convection et onde de gravité

Date and time : The 26-09-2018 at 15h00

Type : thèse

Université qui délivre le diplôme : Sorbonne Université

Location : salle de conférence de l'UFR Terre, Environnement, Biodiversité - Sorbonne Université, Campus de Jussieu (couloir 46-56, 2e étage), Paris
Members of jury :

Mme Ann Carine VANDAELE, IASB, Belgique - Rapporteur

M. Scot RAFKIN, Southwest Research Institute, États-Unis, Rapporteur

M. Riwal PLOUGONVEN, Laboratoire de Météorologie Dynamique, Examinateur et Président du jury

M. Colin WILSON, University of Oxford, Grand-Bretagne, Examinateur

Mme Caroline MULLER, Laboratoire de Météorologie Dynamique, Invité        

M. Sébastien LEBONNOIS, Laboratoire de Météorologie Dynamique, Directeur de thèse

M. Aymeric SPIGA, Laboratoire de Météorologie Dynamique, Directeur de thèse

Summary :

The observations made by the mission Venus Express and Akatsuki gave unprecedented insight of the turbulence of the atmosphere of Venus. The vertical extension of the cloud convective layer as well as the variability with latitude and local time has been studied, small-scale gravity waves have been observed both above and below this convection layer. Despite a stable atmosphere, cellular features have been observed at the top of the cloud at low latitude at noon. Recently large stationnary bow-shape waves have been measured above the main topographic features at low latitude.

In order to address these questions we used the WRF dynamical core to be able to resolve smallscale turbulence. With Large-Eddy Simulations (LES), simulations were performed to resolve the convective activity of the could layer and the induced gravity waves. The vertical extension of the resolved convective layer is from 46 to 55 km, consistent with observations. Small-scale gravity waves are induced by this convective activity with an amplitude less than a Kelvin, smaller than the observations. The background wind has a strong effect on those waves. With obstacle effect, the updrafts above the convection block the flow and force it to go above, waves of more than a Kelvin of amplitude are generated. At noon, the strong absorption of the solar radiation by the unknown ultraviolet absorber induces convection activity at the top of the cloud between 66 and 73 km.With the mesoscale mode, high-resolution topography produces stationary bow-shape waves with amplitude and latitudinal extension consistent with observations. The vertical propagation has been studied, the two low static stability region between 18 to 30 km and 48 to 55 km produce trap lee waves and perturb the waves. Diurnal variation of the near-surface stability of the atmosphere plays a key role on the intensity of the waves. The polar activity was also investigated.In addition, studies about the turbulence in exoplanetary atmosphere, convection inside the brown dwarfs and young giant exoplanet as well as the behavior of the convective activity and its role on the clouds for rocky tidally-locked exoplanet such as Proxima-b were conducted.

Contact :
maxence.lefevre@lmd.jussieu.fr
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