Optical properties of stratospheric aerosols from wildfires and volcanic eruptions constrained by satellite and ground-based lidars – Part I: large scale evolution

Abstract. Stratospheric aerosols exert a major influence on the Earth's radiative balance, atmospheric chemistry, and climate variability. Over the last two decades, the stratospheric aerosol layer has been repeatedly perturbed by explosive volcanic eruptions and, more recently, by extreme wildfire events capable of injecting large amounts of aerosols into the lower stratosphere. Characterizing the long-term evolution of these perturbations is therefore essential for improving our understanding of stratospheric aerosol variability and its climatic impacts. This study is presented in two companion papers. Part I focuses on the large-scale evolution and persistence of major stratospheric aerosol perturbations over the CALIPSO observational period, while Part II investigates the optical properties and early evolution of individual volcanic and wildfire plumes.

In this study, we investigate the large-scale evolution of the stratospheric aerosol layer between 2006 and 2023 using a new dataset Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) Level 1 dataset (L1CC). The analysis combines stratospheric aerosol optical depth (SAOD), scattering ratio (SR), and bulk depolarization with the Global Space-based Stratospheric Aerosol Climatology (GloSSAC), Ozone Mapping and Profiler Suite Limb Profiler (OMPS-LP) observations, Atmospheric Lidar (ATLID) observations aboard EarthCARE, and independent Network for the Detection of Atmospheric Composition Change (NDACC) lidar measurements at the Observatoire de Haute-Provence (44° N) and Lauder (45° S). The corrected dataset is validated against these independent observations, demonstrating its capability to reproduce the timing, magnitude and vertical evolution of the major stratospheric aerosol perturbations observed during the CALIPSO mission.

The observations reveal distinct long-term optical behaviours associated with volcanic eruptions and wildfire events, with volcanic plume properties depending on their ash and sulfate content, whereas wildfire plumes maintain persistently elevated depolarization associated with long-lived carbonaceous aerosols. The combined analysis of SAOD, scattering ratio and bulk depolarization further provides a consistent description of the temporal evolution of the stratospheric aerosol layer over nearly two decades.

Finally, a return-time analysis is introduced to quantify the persistence of individual perturbations. The results demonstrate that recovery of the stratospheric aerosol layer depends not only on the magnitude of the initial aerosol loading but also on injection altitude and subsequent atmospheric evolution. Together, these results provide a homogeneous lidar-based climatology of the large-scale evolution of the stratospheric aerosol layer over the complete CALIPSO mission, and enabling consistent comparisons of the long-term impacts of volcanic eruptions and extreme wildfire events.