The stratosphere dynamics remains largely unexplored in summer and spring. In the context of the ozone layer recovery and the increasing of greenhouse gases emissions, efforts must be provided to improve our knowledge of the dynamical processes driving the stratosphere. Such improvements would lead to better future climate trends estimates. Recently, spring and summer satellites observations revealed occurrences of irreversible air masses transport from the tropics to the Arctic region. However, the associated mechanisms are poorly understood. The present work consists of dynamical and climatological analyses of these events in order to identify their causes and their occurrence frequency. In particular, we focused on the sporadic events, where the intrusion signal persists several months in the polar region, trapped within an anticyclonic anomaly before disappearing in summer. We used MLS/Aura and MIPAS/ENVISAT satellites data, the SPIRALE balloon borne data and the results of the advection model MIMOSA to identify, characterize and quantify these events. Stratospheric dynamical conditions are investigated using the reanalyses data of the ECMWF. Finally, a systematic algorithm to detect low-latitude intrusions has been developed and applied on MIMOSA results to perform a climatology between 1980 and 2011 The results suggest that the frequency of these events, driven by the planetary wave activity, is increasing since the 21st century. Furthermore, their occurrence in spring appears to depend on the stratospheric dynamical evolution during winter and on the tropical region dynamical regime.
