Radiative forcing by volcanic eruptions since 1990, calculated with a chemistry-climate model and a new emission inventory based on vertically resolved satellite measurements

Abstract

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.

Interactive stratospheric aerosol models' response to different amounts and altitudes of SO2 injection during the 1991 Pinatubo eruption

“…The resulting total optical depths, single-scattering albedos, and asymmetry factors are used in radiative transfer calculations which feed back to atmospheric dynamics. The results from EMAC were taken from an existing 30-year transient simulation for comparison (Schallock et al, 2021).…”

Interactive Stratospheric Aerosol models response to different amount and altitude of SO2 injections during the 1991 Pinatubo eruption

“…EMAC is the ECHAM5 general circulation model coupled with Modular Earth Submodel System Atmospheric Chemistry (Brühl et al, 2015(Brühl et al, , 2018Schallock et al, 2021). It contains comprehensive gas-phase and heterogeneous chemistry.…”

“…The resulting optical depths, single scattering albedos and asymmetry factors are used in radiative transfer calculations which feedback to atmospheric dynamics. Volcanic SO 2 injections are entered as 3Dmixing ratio perturbations derived from satellite data using an inventory for the period 1990 to 2019 (Schallock et al, 2021, https://doi.org/10.26050/WDCC/SSIRC_3). For the Pinatubo period also the eruptions of Cerro Hudson, Spurr and Lascar are included.…”

Contrasting Stratospheric Smoke Mass and Lifetime From 2017 Canadian and 2019/2020 Australian Megafires: Global Simulations and Satellite Observations

“…For comparison, in August 1991, 2 months after Mount Pinatubo eruption, the net solar flux at surface lowered by ≈4 W/m 2 , zonally averaged between 40°N and 40°S (Minnis et al., 1993). Globally, during the past three decades, volcanic emissions of sulphate aerosols were estimated to be responsible for an average radiative forcing anomaly of approximately −0.1 W/m 2 (Ge et al., 2016; Schallock et al., 2021; Schmidt et al., 2018).…”