Friday, December 24, 2021

One of the longest-lived ozone holes on record is about to close

Left: Still of animation of the ozone hole on 15th October.
Right: Total column ozone field forecast for Monday 20th December from CAMS showing only a small area with values below 220 DU over the Antarctic.
Credit: Copernicus Atmosphere Monitoring Service, ECMWF

From Copernicus

Scientists from the Copernicus Atmosphere Monitoring Service confirm that the 2021 Antarctic ozone hole has almost reached its end, following a season with a considerably large and prolonged ozone hole.
Its closure will occur only a few days earlier than in 2020, which was the longest lived since 1979.

The Copernicus Atmosphere Monitoring Service (CAMS), implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) on behalf of the European Commission with funding from the European Union, reports that the Antarctic ozone hole has almost reached its end.
Similar to last year’s season, the ozone hole in 2021 will be one of the largest and longest-living ones on record, coming to a close later than 95% of all tracked ozone holes since 1979.

Vincent-Henri Peuch, Director of Copernicus Atmosphere Monitoring Service at ECMWF, comments: “Both the 2020 and 2021 Antarctic ozone holes have been rather large and exceptionally long-lived.
These two longer-than-usual episodes in a row are not a sign that the Montreal Protocol is not working though, as without it, they would have been even larger.
It is because of interannual variability due to meteorological and dynamical conditions that can have an important impact on the magnitude of the ozone hole and are superimposed on the long-term recovery.
CAMS also keeps an eye on the amount of UV radiation reaching the Earth’s surface, and we’ve seen in recent weeks very high UV indexes­ – in excess of 8 – over parts of Antarctica situated below the ozone hole.”
The Montreal Protocol, signed in 1978, is one of the most credited climate action agreements set in place to protect the ozone layer.
The protocol bans harmful chemicals that are linked to ozone destruction and depletion such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs).
These chemicals remain in the atmosphere for long periods of time and reach the stratosphere, where they contribute to ozone depletion.
Thanks to the Montreal Protocol the concentrations of these chemicals are slowly decreasing.
However, because of their long lifetimes it will still take about four decades for the ozone layer to fully recover.
CAMS is contributing to the international efforts of preserving the ozone layer by continually monitoring and delivering high quality data about its current state.
Computer models of the atmosphere are combined with measurements from satellites and in-situ stations to monitor closely the evolution of the phenomenon.
As the stratospheric ozone layer acts as a shield, protecting from potentially harmful ultraviolet radiation, it is of the upmost importance to track its changes.

“CAMS monitors and observes the ozone layer by providing reliable and free-to-access-data based on different types of satellite observations and numerical modelling, which makes the monitoring of the inception, development and closure of the yearly ozone holes possible in a detailed way.
The compiled data, along with our forecasts, allows us to follow the ozone season and compare its development against the ones of the last 40 years”, adds Vincent-Henri Peuch.

How the ozone hole is formed

Chlorine and bromine-containing substances accumulate within the polar vortex where they stay chemically inactive in the darkness.
Temperatures in the vortex can fall to below -78 degrees Celsius and ice crystals in Polar stratospheric clouds can form, which play an important part in the chemical reactions.
As the sun rises over the pole, the sun’s energy releases chemically-active chlorine and bromine atoms in the vortex which rapidly destroy ozone molecules, causing the hole to form.

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