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September 27, 2002
NASA Scientists Observe "Thinning" of Arctic Ozone Layer During 1999-2000 SOLVE Mission
The Arctic ozone layer lost over half of its ozone during the 1999-2000 winter from the same chemical processes that create the Antarctic ozone hole, NASA researchers report.
Scientists observed the "thinning" of the Arctic ozone layer during the SAGE III Ozone Loss and Validation Experiment (SOLVE) and Third European Stratospheric Experiment on Ozone (THESEO) 2000 field campaign. They used five different airborne instruments and numerous other observations from the experiment that together make the most comprehensive set of measurements ever taken to determine Arctic ozone loss.
Ozone destruction increased significantly during the 2000 winter with up to 55 percent of total Arctic ozone lost by March, say scientists in a recently published paper detailing the assessment of ozone loss during SOLVE-THESEO 2000 in the Journal of Geophysical Research.
"Because ozone screens harmful ultraviolet or sun-burning radiation, large losses in spring, when plants are blooming and people are starting to venture outdoors again, can result in biological damage," said Paul Newman an atmospheric scientist at NASA's Goddard Space Flight Center, in Greenbelt, Md. "Hence, the large losses are worrisome from a human health and biota damage perspective."
While there is an expected year-to-year variability in the amount of ozone destruction due to the dynamics or natural motions of the atmosphere, the loss observed during SOLVE-THESEO 2000 exceeded that expectation by twice as much. Scientists discovered this difference when they compared the amount of ozone loss during March 2000 to the average of ozone measurements from every March between 1979-1990 taken by the Total Ozone Mapping Spectrometer (TOMS) satellite instruments. Scientists attribute this additional destruction to atmospheric chemical processes, which are as equally important as dynamics for determining ozone loss.
"The chemistry that is being referred to is the same freon-derived chlorine chemistry that causes the ozone hole over Antarctica," said Edward Browell, an atmospheric scientist at NASA's Langley Research Center in Hampton, Va.
This chemistry depends on cold temperatures, sunlight and the availability of human-produced compounds like chlorofluorocarbons (CFCs) and halons, which have increased in the stratosphere or middle atmosphere over the last 30 years. During cold Arctic winters, polar stratospheric clouds (PSCs) form in the stratosphere. In sunlight, the chlorine and bromine compounds from human-produced gases create chemical reactions with PSC particles that destroy ozone. Arctic temperatures vary every winter as does the amount of ozone destruction. But the greatest amount of loss always occurs during spring when the changing orbit of the Earth allows more sunlight to reach the Arctic.
"[The ozone loss] was a result of the particular conditions of 1999-2000. The last two years have both been rather warm in the Arctic, and hence, ozone has been higher," said Newman. "Nevertheless, the large 2000 loss is indicative of the losses we will see during cold stratospheric winters for the next 10-20 years while chlorine and bromine gases are at high levels."
The ozone loss observed in the Arctic during the 1999-2000 winter is comparable to Antarctic losses, say the scientists, even though the ozone destruction did not create a "hole" in the ozone layer.
"Ozone destruction is more complicated in the Arctic than in Antarctica. Understanding the processes that lead to ozone destruction in the Arctic are very important because it is a more populated area," said Browell. "Currently we don't have an ability to predict accurately the amount of Arctic ozone loss, and uncertainties need to be reduced to forecast the chemical impact on ozone destruction."
NASA scientists will conduct their next field experiment on Arctic ozone during SOLVE II in early 2003 in Kiruna, Sweden. SOLVE II measurements will also validate observations from NASA's SAGE (Stratospheric Aerosol and Gas Experiment) III satellite instrument launched in December 2001.
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AREA OF MISSION OPERATION
SOLVE-THESEO 2000 was a joint effort between scientists from the U.S., Europe, Russia, Canada, and Japan and was the largest field campaign to observe stratospheric ozone changes in the Arctic. The experiment occurred during the 1999-2000 winter, and was primarily based in Kiruna, Sweden.
Image courtesy of NASA Scientific Visualization Studio (SVS)
ARCTIC OZONE LOSS WINTER 1999-2000
On average scientists observed a 55 percent decrease of Arctic ozone in the stratosphere during the 1999-2000 winter. In this image using data from NASA's TOMS Earth Probe, blue regions represent the difference between ozone levels observed in the early 1980s and the 1999-2000 winter.
Image courtesy of NASA Scientific Visualization Studio (SVS)
POLAR STRATOSPHERIC CLOUDS
An image of polar stratospheric clouds (PSCs) observed over Kiruna, Sweden, in January 2000. Extremely low temperatures allow PSCs to form at altitudes approximately near 20 km (12 km) in the stratosphere. The low Arctic temperatures enabled PSCs to last longer during the 1999-2000 winter, causing additional ozone loss.
Image courtesy of the NASA SOLVE Mission
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