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Etude du cycle de vie des cirrus dans la tropopause tropicale à partir des mesures lidar de la campagne d'observation Stratéole2

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Auteur / Autrice : Thomas Lesigne
Direction : Francois Ravetta
Type : Projet de thèse
Discipline(s) : Instrumentation, télédétection, observation et techniques spatiales pour l'océan, l'atmosphère et le climat
Date : Inscription en doctorat le 01/01/2023
Etablissement(s) : Sorbonne université
Ecole(s) doctorale(s) : École doctorale Sciences de l'environnement d'Île-de-France (Paris ; 1992-....)
Partenaire(s) de recherche : Laboratoire : Laboratoire Atmosphères, Milieux, Observations Spatiales
Equipe de recherche : STRATO

Mots clés

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Résumé

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The atmospheric layer near the tropical tropopause (14-18.5 km), referred to as the Tropical Tropopause Layer (TTL), is a key region of the Earth atmosphere and the gateway to the stratosphere. Along their ascent through the extremely cold TTL (<200 K), air parcels undergo ice formation and freeze-drying, which is ultimately responsible for the dryness of the stratosphere, of dramatic importance for stratospheric chemistry and the Earth radiative balance. TTL ice clouds (cirrus) also directly affect the Earth radiative budget. Hence, it is crucial to understand the dynamical, radiative and microphysical processes controlling TTL clouds, in particular given their poor representation in climate models and the strong uncertainty of their response to climate variability and anthropogenic forcing. Among the processes at stake, gravity waves play a major role in shaping the upper tropospheric temperature field, which itself considerably impact the occurrence and life cycle of cirrus clouds. Triggered by deep tropical convection, gravity waves are ubiquitous in the TTL but mostly unresolved in climate models with parameterized convection. Based on satellite or in situ data, recent observational analyses have demonstrated the systematic link between cirrus and wave-induced temperature anomalies. However, these studies were based on fast-moving observational platforms (aircraft, satellite) and could not observe the Lagrangian (air-parcel-following) life cycle of TTL cirrus, which is essential for process studies. The proposed thesis will exploit a unique dataset gathered during long-duration balloon (SPB) flights in the frame of the Strateole-2 project (2019-2024). Strateole-2 is an international effort led by French scientists aiming at in situ and remote-sensing observations of the TTL using SPBs developed by CNES. The balloons drift with the wind for several months at targeted altitudes, which enables quasi-Lagrangian measurements and is well-suited to characterize the Lagrangian cirrus life cycle.