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Ozone Hole 2020
 

Unusual Weather Leads to Ozone Low Over the Arctic

In 2020, ozone concentrations above the Arctic reached a record low for the month of March. In an analysis of satellite observations, scientists found that stratospheric ozone levels reached their lowest point—205 Dobson Units—on March 12, 2020. For comparison, the lowest ozone value observed over the Arctic in a typical March is at least 240 Dobson Units.

While such low levels are unusual, they are not unprecedented in four decades of observations. Similar low ozone levels occurred in the Arctic stratosphere in 1997 and 2011. Such “low” levels for the Arctic are still nearly double the levels found in Antarctic ozone holes.

“Low Arctic ozone like we had this year happens about once per decade,” said Paul Newman, chief scientist for Earth sciences at NASA’s Goddard Space Flight Center and an ozone layer expert. ”For the overall health of the ozone layer, this is concerning since Arctic ozone levels are typically high during March and April.”

The images above show monthly average concentrations of ozone over the Arctic in March 2019 (a typical year) and March 2020, as calculated by the NASA Ozone Watch team. The plot below shows the daily minimum column ozone levels for the past two years and the long-term averages.

In 2020, ozone concentrations above the Arctic reached a record low for the month of March. In an analysis of satellite observations, scientists found that stratospheric ozone levels reached their lowest point—205 Dobson Units—on March 12, 2020. For comparison, the lowest ozone value observed over the Arctic in a typical March is at least 240 Dobson Units.

While such low levels are unusual, they are not unprecedented in four decades of observations. Similar low ozone levels occurred in the Arctic stratosphere in 1997 and 2011. Such “low” levels for the Arctic are still nearly double the levels found in Antarctic ozone holes.

“Low Arctic ozone like we had this year happens about once per decade,” said Paul Newman, chief scientist for Earth sciences at NASA’s Goddard Space Flight Center and an ozone layer expert. ”For the overall health of the ozone layer, this is concerning since Arctic ozone levels are typically high during March and April.”

The images above show monthly average concentrations of ozone over the Arctic in March 2019 (a typical year) and March 2020, as calculated by the NASA Ozone Watch team. The plot below shows the daily minimum column ozone levels for the past two years and the long-term averages.

 

Ozone is a highly reactive molecule comprised of three oxygen atoms; it occurs naturally in small amounts. The stratospheric ozone layer—roughly 10 to 40 kilometers (7 to 25 miles) above Earth’s surface—is a natural sunscreen, absorbing harmful ultraviolet radiation that would otherwise damage plant DNA and harm humans and animals by causing cataracts, skin cancer, and suppressed immune systems.

This year’s Arctic ozone depletion was caused by unusually weak upper atmospheric “wave” events from December 2019 through March 2020. These waves drive masses of air through the upper atmosphere, much like weather fronts in the lower atmosphere, but much bigger in scale. In a typical year, these waves travel upward from the lower atmosphere in middle latitudes and disrupt the circumpolar winds that swirl around the Arctic.

When such waves disrupt polar winds, they bring ozone from other parts of the stratosphere and replenish the reservoir over the Arctic. “Think of it like having a red-paint dollop—low ozone over the North Pole—in a bucket of white paint,” Newman said. “The waves stir the white paint—higher amounts of ozone in the mid-latitudes—with the red paint (or low ozone) contained by the strong jet stream circling around the pole.”

This mixing has a second effect: warming the air over the Arctic. Warmer temperatures then make conditions unfavorable for the formation of polar stratospheric clouds, which are known to promote ozone-depleting reactions by releasing chlorine. Most of the chlorine and bromine in the atmosphere comes from chlorofluorocarbons and halons, the chemically active forms of chlorine and bromine that were once used in refrigerants, foams, and aerosol-spray cans and are now banned by the Montreal Protocol. Upper atmospheric mixing usually shuts down chlorine- and bromine-driven ozone depletion.

From December 2019 through March 2020, however, stratospheric wave events were weak and did not disrupt the circumpolar winds. The winds thus acted like a barrier, preventing ozone from other parts of the atmosphere from replenishing ozone levels over the Arctic. The stratosphere also remained cold in the region, leading to the formation of the polar stratospheric clouds that provoke ozone-depleting reactions.

NASA researchers prefer the term “depletion” for the Arctic since the ozone loss is still much less than the ozone “hole” that forms over Antarctica each September and October. For comparison, ozone levels over Antarctica typically drop to about 120 Dobson Units. The animation above shows the concentrations of ozone over the North Pole from August 1, 2019, to March 31, 2020. The smaller inset shows conditions over the South Pole, which tend to be much more extreme.

“We don’t know what caused the wave dynamics to be weak this year,” Newman said. “But we do know that if we hadn’t stopped putting chlorofluorocarbons into the atmosphere because of the Montreal Protocol, the Arctic depletion t

 

NASA Earth Observatory images and video by Joshua Stevens, using data courtesy of NASA Ozone Watch. Story by Ellen Gray, NASA Earth Science News Team, with Michael Carlowicz.

https://earthobservatory.nasa.gov/images/146588/unusual-weather-leads-to-ozone-low-over-the-arctic?fbclid=IwAR3WnBz3LX3wLAcg5ULvk4rN4WGfBjeYnLg0dMJEQM3NDXp_36hxqAWCUUc

Unusual ozone hole opens over the Arctic

04/06/2020

 Scientists using data from the Copernicus Sentinel-5P satellite have noticed a strong reduction of ozone concentrations over the Arctic. Unusual atmospheric conditions, including freezing temperatures in the stratosphere, have led ozone levels to plummet – causing a ‘mini-hole’ in the ozone layer.

The ozone layer is a natural, protective layer of gas in the stratosphere that shields life from the Sun’s harmful ultraviolet radiation – which is associated with skin cancer and cataracts, as well as other environmental issues.

The ‘ozone hole’ most commonly referenced is the hole over Antarctica, forming each year during autumn.In the past weeks, scientists from the German Aerospace Center (DLR) have noticed the unusually strong depletion of ozone over the northern polar regions. Using data from the Tropomi instrument on the Copernicus Sentinel-5P satellite, they were able to monitor this Arctic ozone hole form in the atmosphere.

In the past, mini ozone holes have occasionally been spotted over the North Pole, but the depletion over the Arctic this year is much larger compared to previous years.

Diego Loyola, from the German Aerospace Center, comments, “The ozone hole we observe over the Arctic this year has a maximum extension of less than 1 million sq km. This is small compared to the Antarctic hole, which can reach a size of around 20 to 25 million sq km with a normal duration of around 3 to 4 months.”

Even though both poles endure ozone losses during winter, the Arctic’s ozone depletion tends to be significantly less than Antarctica. The ozone hole is driven by extremely cold temperatures (below -80°C), sunlight, wind fields and substances such as chlorofluorocarbons (CFCs).

Arctic temperatures do not usually plummet as low as in Antarctica. However, this year, powerful winds flowing around the North Pole trapped cold air within what is known as the ‘polar vortex’ – a circling whirlpool of stratospheric winds.

By the end of the polar winter, the first sunlight over the North Pole initiated this unusually strong ozone depletion – causing the hole to form. However, its size is still small compared to what can usually be observed in the southern hemisphere.

Diego says, “Since 14 March, the ozone columns over the Arctic have decreased to what is normally considered ‘ozone hole levels,’ which are less than 220 Dobson Units. We expect the hole to close again during mid-April 2020.”

Claus Zehner, ESA’s Copernicus Sentinel-5P mission manager, adds, “The Tropomi total ozone measurements are extending Europe’s capability of the continuous global ozone monitoring from space since 1995. In this time, we have not witnessed an ozone hole formation of this size over the Arctic.”

In the 2018 Scientific Assessment of Ozone Depletion, data shows that the ozone layer in parts of the stratosphere has recovered at a rate of 1-3% per decade since 2000. At these projected rates, the Northern Hemisphere and mid-latitude ozone is predicted to recover by around 2030, followed by the Southern Hemisphere around 2050, and polar regions by 2060.

The Tropomi instrument on the Copernicus Sentinel-5P satellite measures a number of trace gases, including aerosol and cloud properties with a global coverage on a daily basis. Given the importance of monitoring air quality and global ozone distribution, the upcoming Copernicus Sentinel-4 and Sentinel-5 missions will monitor key air quality trace gases, stratospheric ozone, and aerosols. As part of the EU’s Copernicus programme, the missions will provide information on air quality, solar radiation and climate monitoring. 

https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-5P/Unusual_ozone_hole_opens_over_the_Arctic

 
Deviation from normal
 
 
 
 
 
 
 
The total ozone maps are based on ground-based measurements available from the World Ozone and Ultraviolet Radiation Data Centre. Preliminary near real-time data from ground-based observations were also used for the most recent maps. Total ozone values are given in Dobson Units. The numbers represent observations taken from ground stations situated at the bottom left corner of the number.

Maps of deviations represent total ozone deviations from the 1978-1988 level estimated using Total Ozone Mapping Spectrometer (TOMS) data for all areas except the Antarctic and from the pre-1980 level estimated using Dobson data over the Antarctic.

Over areas with poor data coverage adjustments are made according to TOMS on Nimbus-7, Meteor-3, ADEOS and Earth Probe satellites. Over the polar night area Dobson and Brewer moon observations and/or NOAA's TIROS Operational Vertical Sounder (TOVS) satellite data are used. TOVS data are also used when the more reliable TOMS data are not available. The mapping algorithm is similar to those used by the WMO Ozone Mapping Centre.

The day part of the “Start date” can specify a day (1 to 31), a mean over the entire month (1-end) or the mean of a “10-day” period during the month (1-10, 11-20 or 21-end, which might be 8 or 9 or 11 days). It must logically correspond to the unit of the “Interval”.