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The ozone hole over Antarctica is a seasonal phenomenon that usually begins to form in mid-August and gradually shrinks throughout November, according to the latest statemnt of Copernicus Atmosphere Monitoring Service. However, in 2023, the ozone hole appeared a few days earlier than usual and has maintained an area of just over 15 million square kilometers since late October.
Every year during the southern spring, substances that deplete ozone start to accumulate in the stratosphere over the South Pole. This accumulation, along with solar radiation, extreme cold temperatures, and polar stratospheric clouds, leads to the formation of an ozone hole, which is a significant reduction in the concentration of ozone in the stratosphere.
The ozone hole typically closes around the end of November when stratospheric temperatures rise. This temperature increase results in a change in the direction of stratospheric winds and the breakdown of the polar vortex, a phenomenon characterized by strong winds circulating high in the atmosphere over Antarctica, isolating cold air over the South Pole.
Unusual season continues
CAMS forecasts suggest that the ozone hole might become the largest ever observed in December. The season has been atypical from the beginning, with an early increase in size, making it the sixth-largest on record. Subsequently, the ozone hole's size reduced quickly but displayed elongation at different intervals, indicating that part of the ozone hole extended beyond the usual calculation area of the 60 degrees south parallel.
The current behavior is likely linked to stratospheric dynamics, particularly the robust polar vortex, rather than chemistry. Warmer temperatures make it challenging to form polar stratospheric clouds, essential for chemical ozone depletion. The ozone hole is expected to persist until the polar vortex breaks down, allowing higher ozone values from mid-latitudes to reach the southern polar stratosphere.
Historical trends and climate impact
CAMS data has consistently shown unusually persistent and large ozone holes in recent years, raising questions about the impact of global warming on stratospheric temperatures. Ozone depletion is influenced by factors such as greenhouse gas emissions, volcanic and wildfire aerosols, and changes in the solar cycle.
Understanding these processes in near-real time is challenging due to the difficulties in gathering observations of the middle and upper stratosphere. Despite reduced emissions of ozone-depleting substances, the large and long-lasting ozone holes in recent years remain a subject of research.
NASA and NOAA have identified the 2023 ozone hole as the 12th single-day record and the 16th largest averaged from September 7 to October 13. However, different agencies use distinct methodologies to measure the ozone hole.
Scientists' perspectives
Atmospheric scientist Dr. Amy H Butler from NOAA suggests that record-low stratospheric temperatures for the time of the year might be contributing to the unusually large and late ozone hole. There's also speculation about the influence of water vapor injected into the stratosphere by the Hunga-Tonga volcano in 2022. Positive Southern Annular Mode events, associated with pressure anomalies around Antarctica, are also considered a potential factor.
Recent research published in Nature Communications focuses on the potential drivers of the recent large Antarctic ozone holes, particularly the peculiar 2020-2022 seasons. The study analyzes the monthly evolution of the ozone hole, highlighting a slight recovery trend in September but a negative trend in October and November since 2001.
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