Evolution passée et future de la composition chimique stratosphérique et ses interactions avec le climat

Virginie Poulain 1
1 STRATO - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : In recent decades, the stratosphere and its chemical composition has undergone significant changes that are beginning to influence the climate. In the stratosphere, the most significant from the point of view of climate change are the ozone layer depletion and the increasing water vapor. Following the increasing of the atmospheric loading of halogen compounds, the ozone layer has depleted over the last thirty years. This laoding has been increasing in the late 90s as a result of the implementation of the Montreal Protocol and its amendments on the control of CFCs emissions. It is therefore expected that the stratospheric ozone found, on the global scale, the levels of 60s (pre-CFC) during this century. However, ozone does not recover its spatial distribution 60s because this distribution depends not only on the laoding of halogen compounds, but also the greenhouse gas concentrations. Indeed, changes in the stratosphere and climate are coupled via chemical, dynamics and radiative mechanisms. In parallel, the wter vpor has increased significantly since the second half of the 20th century. On this long-term trend superimposed very substantial inter-annual fluctuations. For example, observations showed a fairly sharp decline in water vapor in 2001, which remains poorly explained. To better understand the characteristics between the stratospheric chemical composition and climate, chemistry-climate models have been developed during the last decade. Climatologies of these models were evaluated by comparisons with various sets of observations in the context of major international programs such as SPARC/CCMVal. This thesis is rather focused on the assessment of the variability in these models. Vari- ability can be decomposed into two terms: the internal variability (hard to describe) generated from within the system and the forced variability which is generated by external forcing to the system, such as solar activity or loading of halogen compounds. The first part of this thesis focuses on the assessment of the models in terms of inter-annual variability of stratospheric chemical composition, including ozone and water vapor. We are interested not only in the inter-annual variability of stratospheric ozone at NDACC observation stations, but also to external forcings contributions on this variability. Then, we focus on stratospheric water vapor, in particular, on the phenomena of fairly sharp variations (also called ruptures) of the content that can generate a very significant climate forcing. The ability of CCMs to reproduce these rupture is evaluated by comparisons with long time series of observations. Finally, we study the climate forcing of ozone variations, in particular evolution of its radiative forcing until the end of the century and if the evolution of ozone on a global scale may be an indicator of its radiative forcing.
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Virginie Poulain. Evolution passée et future de la composition chimique stratosphérique et ses interactions avec le climat. Sciences de l'environnement. Université Pierre et Marie Curie - Paris VI, 2013. Français. ⟨tel-00909553⟩

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