The unusual stratospheric Arctic winter 2019/2020

Abstract:

In Arctic winter/spring 2019/20 exceptionally low total ozone values of slightly less than 220 DU were observed in mid March within a large stratospheric polar vortex. This was associated with very low temperatures and extensive polar stratospheric cloud formation, a prerequisite for substantial springtime ozone depletion. While large springtime polar ozone losses have been regularly observed above Antarctica since the 1980s (the “ozone hole”), such events occur only sporadically in the Arctic. The winter 2019/20 has some similarity to the Arctic winter 2010/11 which displayed the largest estimated ozone depletion so far observed.

In this presentation, we will use satellite observations of relevant trace gases together with meteorological data from ECMWF to describe the dynamics and chemistry of the spectacular Arctic 2019/20 winter/spring season. Using results from the SLIMCAT chemical transport model (CTM) and ozone observations from S5P/TROPOMI, GOME-2 (column ozone) and OMPS-LP (ozone profiles) chemical ozone loss was evaluated and compared with the previous record Arctic winter 2010/11. The polar vortex averaged column ozone loss in 2019/20 reached 166 DU (36%) by the end of March, which was similar to that in 2010/11. Because of the larger polar vortex area in March 2020 compared to 2010/11, ozone mass loss was correspondingly higher in 2019/20.

The extreme Arctic winter/spring 2019/20, as well as the opposite extreme of the very small Antarctic ozone hole of 2019, are well behaved when considering the linear correlation of seasonal ozone changes in both hemispheres as a function of the average winter eddy heat flux. This implies that the dynamical and chemical processes of polar ozone are well understood. Since the early 1990s there has been about one to two Arctic winters per decade with exceptionally low polar cap temperatures, which appear to be getting colder. We will briefly discuss what we can learn from Arctic winter 2019/20 with respect to the future evolution of ozone as stratospheric halogen sources (e.g. CFCs, HCFCs, Halons etc.) decline as a consequence of the Montreal Protocol phase-out of ozone depleting substances, while manmade climate change increases.