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 inï¬uence 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.
Highlights
Excluding recent history in which large fires have become a major source of aerosols up to the tropopause and above it, stratospheric aerosol particles are mostly of volcanic origin and consist of a mixture of liquid sulfuric acid (H2SO4) and water (H2O) droplets, which are condensed from the gas phase by secondary particle formation
We incorporated stratospheric aerosol, 30 including the sulfur budget, the sulfur chemistry and the radiative transfer into a comprehensive Chemistry Climate Model (CCM), which we have used to gain a better understanding of the interaction of aerosols with the global climate system and ozone
In a previous inventory of volcanic eruptions based on SO2 vertical profiles from Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), we estimated the aerosol radiative forcing from 2002 to 2011 by simulating the evolution of SO2 in the atmosphere reported by Brühl et al (2015) and by 230 improving the resulting time series using aerosol measurements from Bingen et al (2017)
Summary
Excluding recent history in which large fires have become a major source of aerosols up to the tropopause and above it, stratospheric aerosol particles are mostly of volcanic origin and consist of a mixture of liquid sulfuric acid (H2SO4) and water (H2O) droplets, which are condensed from the gas phase by secondary particle formation. Sulfate and ashes from explosive volcanic eruptions can account for the majority of the aerosol burden in the stratosphere 35 during volcanically active periods and cause strong temporal and spatial variations in the concentration and the size distribution of the particles. These changes influence in turn the radiative forcing at tropopause altitudes (or at the top of the atmosphere) and can even have a large impact on the global climate for one to three years after the eruptions (Timmreck, 2012). At the end of 60 section 6 as well as in the final discussion (section 7), the results are discussed in a wider context
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