The ozone hole has closed again (but normality remains far away) – time.news

A record negative year was that of the ozone hole over Antarctica in 2020. The World Meteorological Organization (WMO) specified that at the moment of maximum destruction the area reached an extension of 24.8 million square kilometers affecting almost the entire white continent. This destructive peak was reached on September 20, 2020, growing rapidly starting in mid-August. At the end of December, however, the hole closed again as it does at the end of the spring season in the Southern Hemisphere which lasts on average from August to October. Instead, in the year that has just ended, he went further, reaching the record in permanence as well as being one of the most extensive and profound since the situation has been checked and measured in the last forty years.

Exceptional variability of the phenomenon

The result is in contrast to the previous season of 2019 when the hole was smaller in size and with a shorter stay. Precisely the last two vintages demonstrate the exceptional variability of the phenomenon, helping us to understand the causes that determine it, specifies Oksana Tarasova, head of the Atmospheric Environment Research Division of the OMM. The destruction of ozone is directly linked to the temperature of the stratosphere that the atmospheric layer between 10 and 50 kilometers high. Here the formation of stratospheric clouds, which reveal a considerable importance in the destruction of the precious gas, are formed only at a temperature below minus 78 degrees centigrade. The clouds contain ice crystals that can promote destruction as soon as the arrival of the greatest sunlight of the season triggers chemical reactions between the components, the famous chlorofluorocarbons released by human activity. This is the main reason why the ozone hole only occurs between the end of winter and the beginning of spring.

The polar vortex

Then, when the temperature in the stratosphere begins to rise with the hottest season, the polar vortex that circulates on the pole begins to weaken until it stops and the hole begins to mend itself to close in December, restoring a normal condition. By 2020 the cold polar vortex remained more stable than normal by keeping the ozone layer low temperatures above Antarctica by preventing the arrival of warmer air. The bad result is that the ozone concentration between 20 and 25 kilometers of altitude has reached a value of 94 Dobson, which is the unit of measure by which its presence is assessed. The figure corresponds to one third of the normal values. The lowest value measured in the period between 1986 and 1997 was reached in October 1993 and was 89 Dobsonians. For comparison, in 1970 the minimum value was 300 Dobson.

Normal values ​​in 2060

After the Montreal Protocol in 1987 which established a gradual decrease in the release of ozone-depleting gases, the situation began to improve but over a very long period of time because the persistence of harmful gases is not easy to eliminate. Furthermore, the times are variable because an adverse climatic condition such as that of 2020 can still favor serious damage. However, according to experts from the World Meteorological Organization, the trend and recovery is positive and a potential return of ozone normal values ​​is expected in the critical season for 2060.

January 8, 2021 (change January 12, 2021 | 15:58)

© Time.News

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