Measurements from Europe‘s Copernicus Sentinel-5P satellite show that this year the ozone hole for the period since mid-September is larger in area than the average value for all years since 1979.
The current area of the ozone hole significantly exceeds 20 million square kilometres and is comparable to the values for 2018 and 2015, when the area was about 22.9 and 25.6 square kilometres, respectively. Its largest extent to date was in 2006 when it was about 26.6 square kilometres. Last year’s (2019) value of only 9.3 square kilometres was unusually low.
Over the past few weeks, springtime began in Earth’s southern hemisphere. The sun can increasingly now be seen also at high south polar latitudes. The energy in solar radiation initiates a fatal chemical process there, which leads to the rapid and extensive breakdown of ozone in the atmosphere, causing the so-called Antarctic ozone hole to form. This process, which is a consequence of damaging trace substances (so-called CFCs) formerly introduced into the atmosphere on an industrial scale, has been observed since the 1980s. The destruction takes place in the stratosphere at altitudes above some 15 kilometres. Low temperatures are an important precondition for the breakdown of ozone.
The measurements from TROPOMI on S5P show that this year‘s ozone hole has reached its maximal size of ca. 25 million square kilometres (black dots on the right plot). The ozone hole covers most of the Antarctic continent and its size far exceeds the average (GOME-2/Metop measurements) of the past ten years (dark grey area on the right image).
The ozone hole in 2020 also has one of the lowest ozone values. The ozone minimum measured by TROPOMI/S5P is close to 100 DU (black dots on the right plot) and in comparison with GOME-2/Metop measurements of the past 15 years (grey area on the right image).
Variability in the size of the ozone hole is to a large extent determined by the strength of the polar vortex, a current of strong wind that flows around the Antarctic region like our jet stream. This current of strong wind is an immediate consequence of Earth’s rotation and the large temperature differences between polar and temporal latitudes. If this wind current is strong it functions like a barrier: air masses can no longer be exchanged between polar and temperate latitudes. Therefore, the air masses above polar latitudes become isolated and cool down to especially low temperatures during winter. This year the process was very distinct. Last year, in 2019, the strong air current was highly deformed, the reason being so-called planetary waves in the atmosphere that cause meridionally-oriented airstreams. The polar vortex is compressed and stretched, and sometimes even shoved somewhat away from the pole. Warm air masses can then flow into polar regions, disturbing the chemical ozone breakdown reactor.
Last year the ozone hole was extremely small (see the link on the right to the EOC news item of 16 Sept. 2019, "The 2019 ozone hole – a sign of recovery?"). Compared with previous years, the 2020 ozone hole is one of the most distinct. Ozone reduction is already very extensive at present, with minimal values under 100 DU (values below 220 DU are regarded as an ozone hole).
The image shows the strength of planetary waves in 2018, 2019 and 2020 at about 30 km altitude in the southern hemisphere.
On the whole, the wave activity in all three years is quite similar; but clear differences are to be seen especially in winter (August to October). It is evident that wave activity in the winter months of 2018 and 2020 is quite low, and the ozone hole correspondingly large. In 2019, by contrast, wave activity was noticeably higher, especially at the end of September; the polar vortex is strongly disturbed. These large-scale wave phenomena are currently a subject of research. It is anticipated that because of global warming, in other words, climate change, they could alter in strength and structure.