Autor: Mark Kaufman
You're probably familiar with the infamous ozone hole over Antarctica, caused by damaging and now-illegal chemicals.
But during March and April this year there was a notable zone of depleted ozone — which protects life from the sun's ultraviolet radiation — over the Arctic, too. It closed last week, though it wasn't nearly as robust as the annual Antarctic ozone hole, and it certainly wasn't a big health threat to humanity. (Though it’s always wise to diligently use sun protection, regardless of the ozone layer's condition.)
"It’s unusual but not unexpected," Paul Newman, the chief scientist in the Earth Sciences Division at NASA's Goddard Space Flight Center, said of the recent Arctic ozone hole.
"It’s unusual in that we only have events like this about once per decade," Newman added.
There are two other years on record, 1997 and 2011, when there were similar ozone depletions over the Arctic, explained Antje Innes, a senior scientist at the European Union's Copernicus Atmosphere Monitoring Service. But recent measurements suggest the ozone levels were even lower this year, she said.
Importantly, these recent ozone numbers aren't nearly as low as they are in Antarctica's slowly healing, big ozone hole, which opens up in August through October each year.
"These two are really different animals," said NASA's Newman. "This [Arctic ozone hole] is not comparable to the Antarctic ozone hole."
"If this was happening over the Antarctic we would be shouting for joy," he added, referencing the still significantly lower ozone numbers over Antarctica caused by decades of releasing ozone-depleting gases, like chlorofluorocarbons, or CFCs, into the atmosphere. (Fortunately, scientists discovered the Antarctic ozone hole in 1985, and CFCs were soon banned.)
For reference, on Oct. 12, 2018, ozone levels plummeted to 104 Dobson units (the measurement of ozone in the atmosphere) over Antarctica versus 205 Dobson units over the Arctic on Mar. 12, 2020. (Typically, ozone levels don't drop below 240 Dobson units in the Arctic during March.)
The unprecedented 2020 northern hemisphere #OzoneHole has come to an end. The #PolarVortex split, allowing #ozone-rich air into the Arctic, closely matching last week's forecast from the #CopernicusAtmosphere Monitoring Service.
More on the NH Ozone holebit.ly/39JQRU8
IR AL SIGUIENTE ARTICULO
Ozone columns over large parts of the Arctic have reached record-breaking low values this year, and the ozone layer over the Arctic is severely depleted at altitudes of around 18 km. The last time similarly strong chemical ozone depletion was observed over the Arctic was during spring 2011, and ozone depletion in 2020 seems on course to be even stronger.
The Copernicus Atmosphere Monitoring Service (CAMS*) has been closely following the rather unusual ozone hole that has formed over the Arctic this spring.
While we are used to ozone holes developing over the Antarctic every year during the Austral spring, the conditions needed for such strong ozone depletion are not normally found in the Northern Hemisphere. The Antarctic ozone hole is mainly caused by human-made chemicals including chlorine and bromine that migrate into the stratosphere – a layer of the atmosphere around 10–50 kilometres above sea level. These chemicals accumulate inside the strong polar vortex that develops over the Antarctic every winter where they remain chemically inactive in the darkness. Temperatures in the vortex can fall to below -78 degrees Celsius and polar stratospheric clouds (PSCs) can form, which play an important part in chemical reactions involving the human-made chemicals that lead to ozone depletion once sunlight returns to the area. This depletion has been causing an ozone hole to form annually over the last 35 years, but the 2019 Antarctic ozone hole was actually one of the smallest we have seen during that time.
The Arctic stratosphere is usually less isolated than its Antarctic counterpart because the presence of nearby land masses and mountain ranges disturbs the weather patterns more than in the Southern Hemisphere. This explains why the polar vortex in the Northern Hemisphere is usually weaker and more perturbed than in the Southern Hemisphere, and temperatures do not fall so low. However, in 2020 the Arctic polar vortex has been exceptionally strong and long lived. Furthermore, temperatures in the Arctic stratosphere were low enough for several months at the start of 2020 to allow the formation of PSCs, resulting in large ozone losses over the Arctic.
Ozone depletion over the Arctic in 2020 has been so severe that most of the ozone in the layer between 80 and 50 hPa (an altitude of around 18 km) has been depleted.
Right panel: Mean ozone profiles at Ny-Ålesund from CAMS (yellow/orange) and ozonesondes (black) averaged over the years 2003–2019. The shaded area denotes +/- 1 standard deviation.
(Credit: Copernicus Atmosphere Monitoring Service, ECMWF)
CAMS will continue to monitor the evolution of the Arctic ozone hole over the coming months. Our forecasts suggest that temperatures have now started to increase (see temperature graph above) and observations from the Microwave Limb Sounder instrument on NASA’s Aura satellite show that the stock of active chlorine is exhausted so that ozone depletion will slow down and eventually stop. Once the polar vortex breaks down, ozone-depleted air will mix with ozone-rich air from lower latitudes.
CAMS monitors the ozone layer by combining information from its detailed numerical models of the atmosphere with satellite and ground-based (in situ) observations through a process called data assimilation. Currently, CAMS uses ozone satellite observations from the SBUV-2, OMI, MLS, GOME-2 and Sentinel-5P/TROPOMI instruments.
* CAMS is implemented by the European Centre for Medium-Range Weather Forecasts on behalf of the European Commission.
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