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Ondes et turbulence à la tropopause tropicale et impacts sur les cirrus

Abstract : Atmospheric waves and turbulence and their impacts on cirrus clouds in the Tropical Tropopause Layer (TTL, 14-18 km altitude) are studied using in situ observations, numerical simulations and theoretical approaches.First, long-duration stratospheric balloon measurements are used to analyze Lagrangian temperature and vertical wind fluctuations induced by gravity waves at the tropical tropopause. The amplitude and intermittency of wave fluctuations are assessed, and the observations are compared with resolved wave fluctuations in atmospheric models. Methods to parameterize Lagrangian temperature fluctuations are then discussed.Then, some impacts of waves on cirrus clouds microphysics are examined. We first consider the influence of high frequency gravity waves on the ice nucleation process. Next, we explore the interplay between ice crystal sedimentation and advection by the wind perturbations induced by low frequency waves. At last, we use numerical simulations to investigate the formation of a large-scale cirrus in the TTL. We demonstrate the role of large-scale equatorial waves and quantify the relevance of different processes (dynamics, radiative heating,...) in the cloud evolution.Finally, small-scale wind fluctuations, interpreted as turbulent bursts, are characterized using aircraft measurements from the ATTREX campaign in the tropical Pacific. The impact of the fluctuations on vertical mixing and on the TTL tracer budget is quantified. The vertical transport induced by turbulent mixing is found to be smaller than that induced by mean tropical upwelling, but nonetheless significant.
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Submitted on : Thursday, September 14, 2017 - 6:55:08 PM
Last modification on : Monday, December 14, 2020 - 9:49:31 AM
Long-term archiving on: : Sunday, December 17, 2017 - 2:06:11 PM

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  • HAL Id : tel-01587942, version 1

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Aurélien Podglajen. Ondes et turbulence à la tropopause tropicale et impacts sur les cirrus. Sciences de la Terre. Université Paris sciences et lettres, 2017. Français. ⟨NNT : 2017PSLEE013⟩. ⟨tel-01587942⟩

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