Chemical Evolution of the Exceptional Arctic Stratospheric Winter 2019/2020 Compared to Previous Arctic and Antarctic Winters

Abstract

After the discovery of the Antarctic ozone hole by Farman et al. (1985), the question arose why a similar phenomenon was not observed in the Arctic. In contrast to the Antarctic, ozone depletion in the Arctic is typically much less pronounced and shows a higher interannual variability. This is caused by the significantly higher stratospheric temperatures and higher dynamical activity in the Northern Hemisphere, which are associated with a more pronounced Brewer-Dobson circulation and more downwelling (e.g., Manney et al.

Introduction to Special Collection “The Exceptional Arctic Stratospheric Polar Vortex in 2019/2020: Causes and Consequences”

“…Both observational and modeling results in this special collection thus indicate a progression of polar processing and ozone loss that was in between those typical for the Northern and Southern Hemispheres and emphasize the exceptionally low ozone (Grooβ & Müller, 2021; Manney et al., 2020; Wohltmann et al., 2021), with Wohltmann et al. (2021) noting that “only an additional 21–46 hr below PSC temperatures and in sunlight would have been necessary to reduce ozone to near zero locally”. Though unprecedented in the Arctic, the extreme ozone loss in spring 2020 was still far from the conditions seen in the Antarctic that we refer to as an “ozone hole”.…”

“…Chlorine from observations (e.g., Manney et al., 2020) and models (Grooβ & Müller, 2021; Wohltmann et al., 2021) shows a more Antarctic‐like pattern of chlorine deactivation in that the reformation of ClONO 2 was slower and HCl reformed very rapidly and to high values that far overshot those in fall before chlorine activation—similar to patterns seen in Antarctic spring under very low ozone and denitrified conditions (e.g., Douglass & Kawa, 1999; Douglass et al., 1995). Both observational and modeling results in this special collection thus indicate a progression of polar processing and ozone loss that was in between those typical for the Northern and Southern Hemispheres and emphasize the exceptionally low ozone (Grooβ & Müller, 2021; Manney et al., 2020; Wohltmann et al., 2021), with Wohltmann et al. (2021) noting that “only an additional 21–46 hr below PSC temperatures and in sunlight would have been necessary to reduce ozone to near zero locally”.…”

Numerical Modeling of Ozone Loss in the Exceptional Arctic Stratosphere Winter–Spring of 2020

“…The first scenario (noPSC) did not include the formation of PSCs during the Arctic winter and spring (from 1 December to 15 May north to 60 • N), while the second scenario did not include any chemical ozone destruction (noCHEM) in this area during the same period. Due to the fact that in the upper stratosphere it is difficult to correctly simulate ozone variability without considering chemical reactions [27], in the noCHEM scenario, chemistry was turned off only at altitudes below 10 mb (about 5 of 31 32 km).Comparison of the baseline scenario with these two additional scenarios allowed estimating the periods when the chemical destruction of ozone is most effective after heterogeneous activation on the PSC surface. In addition, based on a comparison of these calculation scenarios, it was possible to assess the comparative role of Dynamic and chemical processes of ozone reduction.…”

“…For the first time in all the years of observations, the analysis of data from a number of selected ozonesondes revealed an extremely strong decrease in the ozone content in the Arctic stratosphere in the spring of 2020, amounting to up to 90% [25]. According to simulations of chemistry and transport model ATLAS [27], very low ozone values inside the Arctic polar vortex in the lower stratosphere were caused by exceptionally long periods in the history of these air masses with low temperatures in sunlight.…”

Signatures of Anomalous Transport in the 2019/2020 Arctic Stratospheric Polar Vortex

“…The stratospheric polar vortex in the 2019/2020 Arctic winter was the strongest, most persistent, and most consistently cold on record (e.g., Lawrence et al., 2020). Persistently low temperatures as well as vortex confinement later in spring than usual resulted in record low ozone in the lower stratospheric vortex (lower than that in 2010/2011, the previous record; e.g., Manney et al., 2020; Wohltmann et al., 2020, 2021; Weber et al., 2021). Such an exceptionally strong stratospheric polar vortex was associated with substantial changes in the middle atmospheric circulation extending through the stratosphere and above (e.g., Lawrence et al., 2020; Lukianova et al., 2021; Ma et al., 2022), as well as coupling with the troposphere (e.g., Lawrence et al., 2020; Rupp et al., 2022).…”