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Abstract:
This paper presents model simulations of stratospheric aerosols with a focus on explosive volcanic eruptions. Using various (occulation and limb based) satellite instruments, with vertical profiles of sulfur dioxide (SO2) from the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) instrument and vertical profiles of aerosol extinction from GOMOS (Global Ozone Monitoring by Occultation of Stars), OSIRIS (Optical Spectrograph and InfraRed Imaging System), and SAGE II (Stratospheric Aerosol and Gas Experiment), we characterised the influence of volcanic aerosols for the period between 1990 and 2019.
We established a volcanic sulfur emission inventory that includes more than 500 eruptions. The identified SO2 perturbations were incorporated as three-dimensional pollution plumes into a chemistry-climate model, which converts the gases into aerosol particles and computes their optical properties. The Aerosol Optical Depth (AOD) and the climate radiative forcing are calculated online. Combined with model improvements, the simulations reproduce the observations of the various satellites.
Slight deviations between the observations and model simulations were found only for the large volcanic eruption of Pinatubo in 1991. This is likely due to either an overestimation of the removal of aerosol particles in the model, or limitations of the satellite measurements, which are related to saturation effects associated with anomalously high aerosol concentrations. Since Pinatubo, only smaller-sized volcanic eruptions have taken place. Weak- and medium-strength volcanic eruptions captured in satellite data and the Smithsonian database typically inject about 10 kt to 50 kt SO2 directly into the upper troposphere/lower stratosphere (UTLS) region or transport it indirectly via convection and advection. Our results show that these relatively smaller eruptions, which occur quite frequently, can nevertheless contribute significantly to the stratospheric aerosol layer and are relevant for the Earth's radiation budget. These eruptions are found to cause a global radiative forcing in the order of −0.1 Wm−2 at the tropopause.
