"We propose to investigate the impact of impulsive ozone perturbations on the middle atmosphere. Impulsive perturbation experiments of increasing complexity will be performed on a stratosphere-mesosphere model and the radiative and dynamical response systematically investigated under a range of conditions. Satellite observations of transient ozone changes retrieved with a new 2-dimensional algorithm will be compared to reanalysis data and model results. The comparison will help identifying sources of atmospheric variability and estimating the characteristics of extreme responses, aiding current global circulation models and our understanding of observed climate change. The project aims at developing a common strategy for analysing and interpreting model results, reanalysis data and short term satellite observations, identifying meaningful diagnostics to be used in dynamically controlled regions of the atmosphere where large non-linear responses can arise. An interdisciplinary approach is needed and it is possible coupling the expertise of the candidate on model perturbation experiments and transient phenomena developed during the previous EU Research Training Network, with the state-of-the-art MIPAS/ENVISAT retrieval capabilities and chemistry knowledge of the host institute. The continuation and extension of close collaborations developed with other members of the previous network will guarantee a continuous interaction with experts of middle atmospheric modelling, stratosphere-troposphere coupling, ion-chemistry modelling and transient luminous events."