Why did the Arctic ozone hole just suddenly close?

Perhaps you're not new to the ozone gap in the skies of Antarctica. In the first months of 2020, there were two big news related to the ozone layer - Earth's ultraviolet shield that you should know. 

• The bad news: Between March and April, in the Arctic sky, there is an area where ozone levels drop significantly.
• Good news : This gap just closed last week.

The ozone layer is the natural shield of the Earth's radiation.

In addition, the ozone layer is not a worrying threat, and its sudden closure, though unusual, does not surprise scientists. According to Professor Paul Newman, director of the Earth Science Division at NASA's Goddard Space Travel Center, this is an event that can occur as often as once every decade.

In the past, twice the ozone hole closure was in 1997 and 2011, also the two skies that appear above the North Pole. However, measurements show that the amount of ozone earlier this year was much smaller than the previous gap. More importantly, recent ozone measurements are not as low as the hole above Antarctica. Currently, this Antarctic ozone layer is slowly recovering.

Despite the same name, the two ozone layer holes at the poles are different in nature and cannot be compared. Professor Newman said that if this sudden closure phenomenon occurred in Antarctica, we could all have cheered.

Why is there an ozone hole in the Arctic?

One of the main reasons is the polar vortex , a vortex of gas that appears at the Pole when it cools. Scientist Antje Innes, working at the Copernicus Atmospheric Monitoring Unit in the EU, said this year's vortex currents were particularly strong and lasted long.

Cold air is locked in the Arctic, no longer flowing into subarctic areas in the Northern Hemisphere. Cold air (up to -78 degrees Celsius) causes clouds to form on the stratosphere, where the ozone shield resides. These cold clouds create the ideal environment for CFCs - artificial substances that damage the ozone layer that have been banned for decades - to interact with sunlight, creating chlorine that erodes the ozone layer.

Moreover, the cyclone prevents ozone-rich air from other places to the North Pole, further reducing the amount of ozone in this cold region. 

The red part represents the air concentrated at the point of the polar cyclone, and they will remain there unless a new air stream blows in from outside.

But last week, the polar vortex melted, allowing ozone-rich air to flow into the North Pole, almost immediately addressing the ozone depletion happening here. Basically, the ozone layer gap in the Arctic has closed. Fortunately, the governments of the countries have banned the circulation of CFC for a long time, so this incident of ozone layer did not leave complicated consequences.

However, science still has unanswered questions: Why is this year's ultra vortex extremely strong? To find the truth, researchers must continue to monitor future fluctuations and analyze recent phenomena in order to find answers.

• Why are ozone layer holes concentrated in Antarctica?
• The ozone hole in Antarctica is beginning to shrink