The Unprecedented Ozone Loss in the Arctic Winter and Spring of 2010/2011 and 2019/2020

Polar ozone depletion has been a major environmental threat for humanity since the late 1980s. The 2011 Arctic winter caught much global attention because of the amount of ozone loss (2.3–3.4 ppmv at 450–475 K potential temperature), and a similar loss was also observed in the 2020 winter (2.5–3.5 ppmv at 400–500 K). Since the difference between the winter of 2010/11 and 2019/20 in terms of ozone loss is small, we investigate the change in terms of polar processing in these years, as that would help future projections of ozone recovery in polar regions. The ozone loss estimated by different methods (passive tracer and vortex descent) shows the highest loss in April in both years 2011 and 2020, but the peak ozone loss altitude was different. The overall ozone loss was more extensive in the lower stratosphere in 2020, but a relatively large loss occurred at higher altitudes in 2011. Prolonged chlorine activation was evident in 2020, longer than that in 2011, which also enhanced loss in the lower stratosphere in 2020. The situation in 2020 resulted in very small values of column ozone, which were below 220 DU for more than 3 weeks, and a near-complete ozone loss (93%) at certain altitudes in the lower stratosphere. The ozone loss in 2020 was similar to that in the Antarctic and was triggered by the presence of a strong and stable polar vortex with zonal winds of constant velocity (40–45 ms–1) and temperature conditions favoring large areas of polar stratospheric clouds (PSCs) (10 million km2) for most of the winter. The relatively lower values of momentum flux suggest that the tropospheric forcing was lower in 2020. Therefore, both winters had less disturbed and long-lasting polar vortices allowing lower temperatures, large areas of PSCs, and longer periods of severe chlorine activation, which in turn led to the record-breaking ozone loss of the levels found in the Antarctic vortex for some days