Quantifying SAGE II (1984–2005) and SAGE III/ISS (2017–2022) observations of smoke in the stratosphere

Using a common analysis approach for data sets produced by the Stratospheric Aerosol and Gas Experiment instruments SAGE II and SAGE III/ISS, we identify 13 likely smoke events based on enhancements in the aerosol extinction coefficient. Nine of these are sufficiently large compared to ambient aeros...

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Bibliographic Details
Published in:	Atmospheric chemistry and physics 2023-09, Vol.23 (18), p.10361-10381
Main Authors:	Thomason, Larry W., Knepp, Travis
Format:	Article
Language:	eng
Subjects:	Aerosol extinction Aerosol observations Aerosols Astronomical instruments Asymptotes Climate Coefficients Datasets Extinction Extinction coefficient Forest & brush fires Latitude Lower stratosphere Northern Hemisphere Optical analysis Optical thickness Ozone SAGE satellite Smoke Stratosphere Sulfur Summer
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Summary:	Using a common analysis approach for data sets produced by the Stratospheric Aerosol and Gas Experiment instruments SAGE II and SAGE III/ISS, we identify 13 likely smoke events based on enhancements in the aerosol extinction coefficient. Nine of these are sufficiently large compared to ambient aerosol levels to compute mean mid-latitude 1020 nm optical depth enhancements that range from 0.0005 to 0.011. We also note that, for large events, the 525 to 1020 nm aerosol extinction coefficient ratio asymptotes at a high extinction coefficient to values between 2 and 3, suggesting that the aerosol radius is relatively small (< 0.3 µm) and relatively consistent from event to event. Most of these events are primarily confined to the lower stratosphere and rarely can be observed above 20 km. We also infer an increase in the frequency of smoke events between the SAGE II (1984–1991, 1996–2005) and SAGE III/ISS (2017-present) periods by almost a factor of 2 and also note that the two largest events occur in the latter data set. However, given the low frequencies overall, we are not confident that the differences can be attributed to changes between the two periods. We also attempt to disentangle the mixing of aerosol in the Northern Hemisphere summer of 1991 from a pyrocumulus event (Baie-Comeau, Quebec) and Mt. Pinatubo and conclude that, while there is evidence for smoke in the lower stratosphere, virtually all of the enhanced aerosol observations in the northern mid-latitudes in the summer of 1991 are associated with the Mt. Pinatubo eruption.
ISSN:	1680-7324 1680-7316 1680-7324