Global Warming

Arctic stratospheric ozone depletion hits record low

Ozone levels above the Arctic reached a record low for March, NASA researchers report. An analysis of satellite observations show that ozone levels reached their lowest point on 12 March, at 205 Dobson units.

While such low levels are rare, they are not unprecedented. Similar low ozone levels occurred in the upper atmosphere, or stratosphere, in 1997 and 2011. In comparison, the lowest March ozone value observed in the Arctic is usually around 240 Dobson units.

March 12, 2019, shows in reds and yellows the higher concentration of stratospheric ozone over the Arctic which are much more typical from year to year. Usually, from December through March, waves in the upper atmosphere disrupt the circumpolar winds and cause the mixing of ozone brought from the mid-latitudes as well as warming that leads to less ozone depletion.

“This year’s low Arctic ozone happens about once per decade,” says Paul Newman, chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center. “For the overall health of the ozone layer, this is concerning since Arctic ozone levels are typically high during March and April.”

The March Arctic ozone depletion was caused by a combination of factors that arose due to unusually weak upper atmospheric “wave” events from December through March. These waves drive movements of air through the upper atmosphere akin to weather systems that we experience in the lower atmosphere, but much bigger in scale.

In a typical year, these waves travel upward from the mid-latitude lower atmosphere to disrupt the circumpolar winds that swirl around the Arctic. When they disrupt the polar winds, they do two things. First, they bring with them ozone from other parts of the stratosphere, replenishing the reservoir over the Arctic.

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