Monitoring Stratospheric Aerosols over Europe: A 16-Year CALIPSO Dataset Analysis (2007–2022)

Abstract. Stratospheric aerosols exert strong radiative and dynamical impacts due to their long residence times and efficient transport. Using CALIPSO Level 2 version 4.51 profiles, we develop a 16-year (2007–2022) climatology of stratospheric aerosol occurrence, vertical structure, subtype composition, and optical depth over Europe, analyzing nighttime overpasses across 12 subregions. The record captures the dominant influence of major volcanic eruptions (Okmok and Kasatochi 2008, Sarychev Peak 2009, Grímsvötn and Nabro 2011, Raikoke 2019) and pyrocumulonimbus-driven wildfire events (e.g., Western Canada 2007, Pacific Northwest Event (PNW) 2017, Siberia 2019–2022). These episodic injections drive strong interannual variability, with annual mean nighttime stratospheric aerosol optical depth (sAOD) ranging from 0.032 in 2007 to a peak of 0.067 in 2017. Vertical distributions broaden over time, with frequent detections reaching heights of 17–19 km and extreme cases up to ~29.8 km, especially following Raikoke’s eruption and major Siberian fire seasons. Subtype analysis reveals sulfate dominance in northern regions and smoke-driven anomalies during major wildfire years, while southern regions show larger unclassified fractions. While no monotonic trend is found, analysis reveals a change-point after 2016, marking a transition to a higher-loading regime. These results highlight the strongly event-driven nature of European stratospheric aerosol variability and CALIPSO’s key role in long term monitoring of volcanic and wildfire impacts on the lower stratosphere.