The goal of the proposed ISSI team is to re-assess the ozone, temperature and potential dynamical signatures of energetic particle precipitation (EPP) from the stratosphere down to the troposphere in existing, state-of-the-art global atmospheric re-analyses. While some studies attributed large surface temperature anomalies to geomagnetic activity in re-analyses, these findings remain highly controversial. The team will primarily focus on re-analyses with high vertical extension and relevant satellite data assimilation. Supporting model studies will help quantify the impact of extreme geomagnetic activity on atmospheric composition, temperature and dynamics, and to provide an envelope for what could be found in re-analyses. A main objective is the quantitative estimation of these signatures, including their temporal and spatial statistical significance. A secondary objective is to provide guidelines for next-generation re-analysis development, in particular concerning assimilation and treatment of ozone.