Le mardi 10 mai 2022, Daniele MINGANTI présentera l'examen en vue de l’obtention du grade académique de Docteur en Sciences (Collège de doctorat en Sciences spatiales) sous la direction de Emmanuel MAHIEU et Simon CHABRILLAT. 

Cette épreuve consistera en la défense publique d’une dissertation intitulée :

« Evaluating the stratospheric circulation and its variability in a Chemistry-Climate Model with reanalyses and observations of nitrous oxide ».

Abstract

The circulation in the atmosphere transports air masses for thousands of kilometers and is closely related to its chemical composition through several physical and chemical processes that affect the climate. In the stratosphere (the layer between approximately 10 and 50 km above the surface), the Brewer-Dobson Circulation (BDC) transports air masses from the Tropics toward the polar latitudes. Consequently, the BDC determines the distribution in the stratosphere of chemical compounds and the thermal structure of the stratosphere. Because of the increase of greenhouse gases and the consequent climate change, climate models simulate an acceleration of the BDC. On the other hand, indirect observations do not show significant changes in the BDC. It is then crucial to better understand the BDC changes in the past decades, in order to better predict its possible future changes.
We investigate the BDC changes in the past decades through their impact on the changes of the long-lived tracer nitrous oxide in the stratosphere. We evaluate those changes in the Whole Atmosphere Community-Climate Model (WACCM) and compare them to observations from satellite and ground-based instruments, and simulations from a chemistry-transport model (CTM) driven by meteorological reanalyses. The observations and the CTM simulations showed asymmetrical changes in the BDC in the past decade, with an intensification in the Southern Hemisphere compared to the Northern Hemisphere. However, this asymmetry is weaker in the WACCM simulations. This diversity indicates that climate change impacts the BDC differently in the Southern and Northern hemispheres, and that this difference is more prominent in reality than in the WACCM climate model.

Le Jury sera composé de :

Mme M. GREGOIRE (Présidente), Mme et MM. M. ABALOS (UCM, Spain), S. CHABRILLAT (BIRA-IASB, Co-promoteur), X. FETTWEIS, E. MAHIEU (Promoteur), G. MUNHOVEN (Secrétaire)