The Unusual Stratospheric Arctic Winter 2019/20: Chemical Ozone Loss From Satellite Observations and TOMCAT Chemical Transport Model

Satellite observations of relevant trace gases and meteorological data from ERA5 were used to describe the dynamics and chemistry of the spectacular Arctic 2019/20 winter/spring season. Exceptionally low total ozone values of slightly less than 220 DU were observed in mid-March within an unusually large stratospheric polar vortex. Very high OClO and very low NO2 column amounts observed by GOME-2A were indicative of unusually large active chlorine levels and significant denitrification, which likely contributed to large chemical ozone loss. Using results from the TOMCAT chemical transport model (CTM) and ozone observations from S5P/TROPOMI, GOME-2 (total column), SCIAMACHY, and OMPS-LP (vertical profiles), chemical ozone loss was evaluated and compared with the previous record Arctic winter 2010/11. The polar-vortex-averaged total column ozone loss in 2019/20 reached 88 DU (23%) and 106 DU (28%) based upon observations and model, respectively, by the end of March, which was similar to that derived for 2010/11. The maximum ozone loss (similar to 80%) observed by OMPS-LP was near the 450 K potential temperature level (similar to 18 km altitude). Because of the larger polar vortex area in March 2020 compared to March 2011 (about 25% at 450 K), ozone mass loss was larger in Arctic winter 2019/20. It is shown that Arctic cap temperatures were at a record 40-year low in winter, suggesting that Arctic cold winters are getting colder. Tropical UTLS temperatures show an apparent upward trend during the last two decades that may indicate a weakening of the Brewer-Dobson circulation and strengthening of the polar vortex.

Automated summary

This study describes the dynamics and chemistry of the Arctic 2019/20 winter/spring season using satellite observations and chemical models, comparing the results with the previous record Arctic winter 2010/11. The findings suggest that the chemical ozone loss in 2019/20 was similar to that of 2010/11, and the Arctic cap temperatures hit a 40-year low in the winter, indicating further cooling in Arctic winters.