Abstract
Abstract. Volcanic SO2 column amount and injection height retrieved from the Ozone Monitoring Instrument (OMI) with the Extended Iterative Spectral Fitting (EISF) technique are used to initialize a global chemistry transport model (GEOS-Chem) to simulate the atmospheric transport and lifecycle of volcanic SO2 and sulfate aerosol from the 2008 Kasatochi eruption, and to subsequently estimate the direct shortwave, top-of-the-atmosphere radiative forcing of the volcanic sulfate aerosol. Analysis shows that the integrated use of OMI SO2 plume height in GEOS-Chem yields: (a) good agreement of the temporal evolution of 3-D volcanic sulfate distributions between model simulations and satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP), and (b) an e-folding time for volcanic SO2 that is consistent with OMI measurements, reflecting SO2 oxidation in the upper troposphere and stratosphere is reliably represented in the model. However, a consistent (~25%) low bias is found in the GEOS-Chem simulated SO2 burden, and is likely due to a high (~20%) bias of cloud liquid water amount (as compared to the MODIS cloud product) and the resultant stronger SO2 oxidation in the GEOS meteorological data during the first week after eruption when part of SO2 underwent aqueous-phase oxidation in clouds. Radiative transfer calculations show that the forcing by Kasatochi volcanic sulfate aerosol becomes negligible 6 months after the eruption, but its global average over the first month is −1.3 Wm−2, with the majority of the forcing-influenced region located north of 20° N, and with daily peak values up to −2 Wm−2 on days 16–17. Sensitivity experiments show that every 2 km decrease of SO2 injection height in the GEOS-Chem simulations will result in a ~25 % decrease in volcanic sulfate forcing; similar sensitivity but opposite sign also holds for a 0.03 μm increase of geometric radius of the volcanic aerosol particles. Both sensitivities highlight the need to characterize the SO2 plume height and aerosol particle size from space. While more research efforts are warranted, this study is among the first to assimilate both satellite-based SO2 plume height and amount into a chemical transport model for an improved simulation of volcanic SO2 and sulfate transport.
Highlights
SO2 plume height in Goddard Earth Observing System (GEOS)-Chem yields: (a) good agreement of the temporal evolution of 3-D volcanic sulfate distributions between model simulations and satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthoggeometric radius of the volcanic aerosol particles
With the use of the Ozone Monitoring Instrument (OMI) Extended Iterative Spectral Fitting (EISF)-based SO2 product to initialize the SO2 distribution in GEOS-Chem, the simulated lifetime as well as the spatial distribution and temporal evolution of the volcanic SO2 burden in the atmosphere after the eruption are both in good agreement with OMI SO2 observations, suggesting that the oxidation of SO2 in the stratosphere is reliably represented in GEOS-Chem
A consistent low (∼25 %) bias is found in the GEOS-Chem simulated SO2 burden, and comparison with MODIS cloud products indicates that this is likely due to a high (∼20 %) bias in cloud liquid water amount and a resultant stronger oxidation of SO2 in the GEOS meteorological data during the first week after the eruption when part of SO2 is oxidized by clouds
Summary
SO2 plume height in GEOS-Chem yields: (a) good agreement of the temporal evolution of 3-D volcanic sulfate distributions between model simulations and satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthoggeometric radius of the volcanic aerosol particles. Both sensitivities highlight the nHeeyddtoroclhoargacyteraiznedthe SO2 plume height search aenffdoratesraorseolwpaarrrtaincltEeedas,iztrhetihsfrsoStmudysyspiatsceeam.mWonhgilethme ofirrestrteoassimilate both satellite-based SOS2cpileumnecheeisght and amount onal Polarisation (CALIOP), and (b) an e-folding time for into a chemical transport model for an improved simulation volcanic SO2 that is consistent with OMI measurements, reflecting SO2 oxidation in the upper troposphere and stratoof volcanic SO2 and sulfate transport. Atmospheric sulfate aerosols play an essential role in atmospheric radiative transfer by scattering and absorbing solar eruption when part of SO2 underwent aqueous-phase oxi- and terrestrial radiation (HanSseonleidt aEl., a19rt7h8; Toon, 1982)
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