October 19, 2020

The Antarctic ozone hole is enlarged by a stable polar vortex


Hole in the ozone layer.

Hole in the ozone layer.
EP

He ozone hole that occurs annually on the Antarctica is in 2020 one of the largest and deepest in recent years. Analysis shows that the hole has reached its maximum size.

The ozone hole of 2020 grew rapidly since mid-August and peaked at around 15 million miles squares in early October. It now covers 23 million square kilometers, above the average for the past decade and spans most of the Antarctic continent.

Ozone Watch of the POT reports a lower value of 95 Dobson units recorded on October 1. Scientists are seeing signs that the 2020 ozone hole appears to have reached its maximum extent.

“There is a great variability in the extent to which ozone hole events develop each year. The ozone hole of 2020 looks like the one in 2018, which was also a fairly large hole, and it is definitely at the top of the pack of the last fifteen years or so, “Vincent-Henri Peuch, Director of the Copernicus Atmosphere Monitoring Service at ECMWF.

“With sunlight returning to the South Pole in recent weeks, we saw continued ozone depletion in the area. After the unusually small and short-lived ozone hole in 2019, which was driven by special weather conditions, we are recording a pretty big one again this year, which confirms that we must continue to apply the Montreal Protocol that prohibits the emissions of chemicals that deplete the ozone layer. ”

He Montreal Protocol bans emissions of ozone-depleting chemicals. Since the halocarbon ban, the ozone layer has been slowly recovering; the data clearly show a decreasing trend in the area of ​​the ozone hole.

The latest Scientific Assessment of Ozone Depletion from WMO and the WMO Program United Nations for the Environment, published in 2018, concluded that the ozone layer is on the way to recovery and possible return of ozone values ​​over Antarctica to pre-1980 levels by 2060.

Driven by the cold

The great ozone hole in 2020 has been driven by a strong, stable and cold polar vortex, which kept the temperature of the ozone layer over Antarctica constantly cool.

Ozone depletion is directly related to temperature in the stratosphere, which is the layer of the atmosphere between about 10 km and about 50 km in altitude. This is because polar stratospheric clouds, which play an important role in the chemical destruction of ozone, only form at temperatures below -78 ° C.

These polar stratospheric clouds contain ice crystals that can convert non-reactive compounds into reactive compounds, which can then rapidly destroy ozone as soon as sunlight is available to start chemical reactions. Is dependence on polar stratospheric clouds and solar radiation it is the main reason why the ozone hole is only seen in late winter or early spring.

It has been observed that stratospheric ozone concentrations have been reduced to near zero values ​​in Antarctica around 20-25 km altitude, with the depth of the ozone layer reaching just below 100 Dobson units, about a third of its typical value outside of ozone hole events.

During the southern hemisphere’s spring season (August-October), the ozone hole over Antarctica increases in size, peaking between mid-September and mid-October. When high temperatures in the atmosphere (stratosphere) begin to rise in late spring in the southern hemisphere, ozone depletion slows down, the polar vortex weakens and eventually decomposes, and by the end of December ozone levels return to The normality.

.



Source link