The fourth largest Southern Hemisphere ozone hole is at the end of November

This 2023 season, the ozone hole over Antarctica is puzzling because of its unusual shape. Copernicus Atmospheric Monitoring Service (CAMS) data showed that in late November, the size of the ozone hole in the Southern Hemisphere had a series of rebounds, decreasing until it normally closed. This behavior raises questions about what’s behind another strange ozone hole season.

The Southern Hemisphere ozone hole is unusually large and typically shrinks until it closes completely in December. Instead, the area of ​​the ozone hole has remained almost unchanged since late October, with continued recovery, at about 15 km2, making it the fourth largest since November 27.

Southern Hemisphere ozone hole area after November 27. 2023 is the 4th largest. Credit: CAMS

The CAMS forecast indicates that the ozone hole will become the largest ever seen in December. CAMS reports that the season has been different since its inception, with an early increase in size to become the 6th largest on records that began in 1979. After that, the size of the ozone hole quickly decreased and returned to the average but stretched out at different times, suggesting that the ozone hole area is outside the 60 degree south parallel region where it is calculated.

Because temperatures are too warm to form polar stratospheric clouds that facilitate chemical ozone depletion, the current situation is linked to the dynamics of the stratosphere and a relatively strong polar vortex rather than chemistry. The ozone hole persists until the polar vortex decays, allowing higher ozone values ​​from the midlatitudes to reach the southern polar stratosphere.

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CAMS data showed unusually long and large ozone holes during the 2020–2022 seasons, with a record late end date in 2020 (28 December, according to CAMS data).

CAMS Director Vincent-Henri Peuch comments: „Since signing the Montreal Protocol, we have drastically reduced our emissions of ozone-depleting substances, allowing space for their recovery in the atmosphere to begin. This is a long process, involving many fluctuating factors. A proper understanding of how the ozone layer is formed is essential. must be monitored. The success of the Montreal Protocol is a testament to how effective measures to protect the global climate can be.”

3D view of ozone hole growth in 2023

The behavior of the Antarctic ozone hole in recent years prompts questions about the impact of global warming, which tends to cool stratospheric temperatures, but also about changes in stratospheric chemistry and dynamics. Ozone depletion is believed to be affected by greenhouse gas emissions, volcanic and wildfire aerosols, or changes in the solar cycle.

Collecting observations of the middle and upper stratosphere is challenging, so it is very difficult to understand the processes in real time, so despite the reduction of emissions of ozone-depleting substances in recent years, large and persistent ozone holes are still a question of research.

It is also yet to be determined whether the last ozone hole seasons are related to climate change or reflect a long-term trend of delaying ozone recovery.

NASA and NOAA reported the 2023 ozone hole as the 12th single-day record and 16th largest averaged from September 7 to October 13. Different agencies use different methods to measure the ozone hole.

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CAMS defines the ozone hole region where total column values ​​are 220 Dobson units below the 60 degree south parallel pole.

According to Doctor Amy H Butler, an atmospheric scientist at NOAA, said stratospheric temperatures could mark daily record lows for this time of year, leading to this unusually large and delayed ozone hole. Dr. Butler, like many scientists, suggests a possible influence of water vapor injected into the stratosphere by the Hanga-Tonka volcano in 2022. But Dr. Butler points to research that positive southern ring events may be delayed during the austral summer. „end stratospheric warming” that normally closes the ozone hole. A positive southern annual mode is associated with periods of higher than normal pressure in regions around Antarctica and lower than average pressure over Antarctica.

A recent study Published in Nature Communications Focus on „Potential Drivers of Recent Large Antarctic Ozone Holes”. Noting the 2020-2022 ozone hole seasons, „Large, long-lived ozone holes reappear in Antarctica.” According to the paper.

The authors examine the monthly evolution of the ozone hole because September is considered the most important indicator of changes in atmospheric chemistry, while October and November are considered to be dominated by stratospheric dynamics.

The research points to a slight recovery in September, reversing the negative trend seen in October and November since 2001. Also, the researchers found a significant reduction in the total column of ozone from 2004 to 2022 in the center of the ozone hole.

The ozone layer protects life on Earth from harmful ultraviolet (UV) radiation. The ozone hole has an impact on atmospheric circulation, particularly in the Southern Hemisphere.

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During the austral spring, ozone depletion products accumulated in the stratosphere interact with solar radiation and stratospheric clouds, fueled by extremely cold temperatures, forming what we now call the ozone hole.

In 1987, a few years after the ozone hole theory was confirmed, the Montreal Protocol agreed to the ban of ozone-depleting substances. The agreement is considered the first global effort to protect the planet. And while this success may avoid further damage to the ozone layer, many other factors affect ozone depletion and therefore delay recovery.

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