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

Abstract

Abstract. 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.

Producing aerosol size distributions consistent with optical particle counters measurements using space-based measurements of aerosol extinction coefficient

“…This is usually a very appropriate assumption, but significant exceptions can occur particularly following injections of smoke into the stratosphere or ash and, to a lesser extent, by the presence of organic aerosol or other non-absorbing, non-sulfuric acid aerosol. While several large smoke events have occurred over the past decade, they are a relatively minor component of the SAGE II aerosol record (Thomason and Knepp, 2023) and will not be considered further in this discussion though for some specific instances and for other instruments including the on-going SAGE III/ISS mission, composition cannot be as easily ignored. Using only WOPC data, we compute three sets of ratios (the SAD to 1020 nm extinction coefficient ratio (SADR), the VD to 1020 nm extinction coefficient ratio (VDR) and the 525 to 1020 nm extinction coefficient ratio (R)) in two altitude ranges (13 to 19.0 and 19.5 to 25 km) for the period where WOPC overlaps with the SAGE II mission.…”

Does the Asian Summer Monsoon Play a Role in the Stratospheric Aerosol Budget of the Arctic?

“…This observation is becoming more frequent in recent years (Zielinski et al, 2020). According to satellite-based studies of global extinction results wild fires can only be found in the lowermost part of the stratosphere with a relatively short lifetime (Thomason and Knepp, 2023). Therefore, the annual cycle with its natural variability and the origin of the Arctic stratospheric aerosol layer is important.…”