Modulation of stratospheric aerosol composition by volcanic eruptions and wildfires from the 18-yr CALIPSO observation record
Résumé
Stratospheric aerosol plays a large role in the chemical and radiative balance of the
atmosphere. Explosive volcanic eruptions may directly inject SO2 and ash into the
stratosphere, leading to significant perturbations of stratospheric aerosol burden at
hemispheric and global scales, lasting from several months to several years. Another
important emerging source of particulate matter in the stratosphere is wildfires, whose
stratospheric impact is becoming increasingly important. Recent studies have demonstrated
the self-lofting capacity of wildfire smoke aerosols, which prolongs their stratospheric
residence time.
Here we use the entire CALIPSO observation record to characterize the perturbations of
stratospheric aerosol composition by various volcanic eruptions and wildfire-driven pyro-
convection. We use CALIOP L1B data at 532 nm to compute the cloud-filtered weekly-
zonal averages of scattering ratio and depolarization. The cloud filtering is done by applying
a threshold of 10% on the raw volume depolarization. The resulting dataset is used to
identify the perturbations of stratospheric aerosol load, to quantify their longevity, and to
characterize the meridional and vertical evolution of volcanic and wildfire aerosols. The
depolarization data allows for distinguishing between sulphates, ash and smoke aerosols.
In this study, we focus on the most significant perturbations of stratospheric aerosol load
during the CALIPSO era, namely the 2015 Calbuco, the 2019 Raikoke and the 2022 Hunga
eruptions as well as the 2019/20 “Black Summer” Australian megafires. The analysis reveals
contrasting behaviour of the volcanic and wildfire plumes in terms of their vertical
evolution. We also find substantial differences in the aerosol composition of volcanic
plumes from the various eruptions.