The Antarctic ozone hole during 2020

Abstract

The Antarctic ozone hole remains the focus of scientific attention because of its importance to the health of the biosphere and its influence on the climate of the southern hemisphere. Here we examine the general characteristics of the 2020 Antarctic ozone hole using a variety of observational and reanalysis data and compare and contrast its behaviour with earlier years. The main feature of the 2020 ozone hole was its relatively large size, and persistence to the beginning of the 2020/2021 summer, with new maximum records being set for the ozone hole daily area and ozone mass deficit during November and December. This was in strong contrast to 2019 when the ozone hole was one of the smallest observed. We show that a key factor in 2020 was the relative stability and strength of the stratospheric polar vortex, which allowed low temperatures in the Antarctic lower stratosphere to enhance ozone depletion reactions in relative isolation from the rest of the global atmosphere. These conditions were associated with relatively weak Rossby wave activity at high southern latitudes that occurred during the strengthening westerly phase of the Quasi Biennial Oscillation as well as the emerging La Niña phase of the El Niño Southern Oscillation. A consequence of the conditions in early summer was the measurement of new maximum values of ultraviolet radiation at Australia's three Antarctic research stations of Mawson, Davis and Casey. Indications of anomalous chlorine partitioning above Arrival Heights in Antarctica prior to the 2020 winter are provided, which may relate to effects from the 2019/2020 Australian wildfires. We also examine the effect of the downward coupling of the 2020 ozone hole to the climate of the wider southern hemisphere, which showed regional influences on surface temperature and precipitation in common with other strong vortex years.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021

“…These conditions led to the longest-lived Antarctic ozone hole in the observational record. Consequently, record-low total ozone columns in November and December 2020 resulted in unusually high levels of UV-B radiation (280-315 nm) in the Antarctic region [8,10]. At Arrival Heights (78° S), the UV index (UVI) reached a new all-time site record of 7.8 on 23 December (Fig.…”

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

“…Nevertheless, it appears likely that the combined effects of climate change and ozone depletion could have impacted both the timing and magnitude of these wildfires with considerable consequences for ecosystems in this region. In contrast to 2019, a strong and persistent Antarctic ozone hole occurred in 2020 and 2021 [ 54 , 74 – 76 ] and this led to record surface UV irradiances at several sites across East Antarctica during early summer. It has been suggested that the Australian wildfires that occurred during the previous summer contributed to this strong ozone loss [ 18 , 54 – 56 , 71 , 72 , 74 ].…”

“… In contrast to 2019, a strong and persistent Antarctic ozone hole occurred in 2020 and 2021 [ 54 , 74 – 76 ] and this led to record surface UV irradiances at several sites across East Antarctica during early summer. It has been suggested that the Australian wildfires that occurred during the previous summer contributed to this strong ozone loss [ 18 , 54 – 56 , 71 , 72 , 74 ]. There is evidence that increased ozone depletion has tended to delay the annual breakdown of the Antarctic stratospheric vortex [ 77 ].…”

Antarctic planetary wave spectrum under different polar vortex conditions in 2019 and 2020 based on total ozone column data

“…Significant minor Antarctic stratospheric warmings occurred in September 1988 (Kanzawa & Kawaguchi, 1990) and September 2019(Yamazaki et al, 2020Milinevsky et al, 2020;Smale et al, 2021;Roy et al, 2022). The warming in 2019 is particularly significant because it came close to reversing the zonal wind at 10 hPa (Rao et al, 2020;Liu et al, 2022), and the stratospheric disturbance has been shown to have significant influences on the Quasi-Biennial Oscillation (QBO) (Anstey et al, 2021) as well as the climate in parts of the Southern Hemisphere, particularly Australia (Lim et al, 2021;Klekociuk et al, 2022).…”

“…Additionally, the QBO was in an easterly phase which would also tend to weaken the vortex (Baldwin & Dunkerton, 1998;Klekociuk et al, 2021). On the contrary, in 2020, the prevailing climate modes included a developing La Niña and a westerly QBO (Klekociuk et al, 2022).…”