Nitrogen oxide and nitrogen dioxide gases in the upper stratosphere climbed to their highest levels in at least two decades in spring 2004, scientists report. The increases led to ozone reductions of up to 60 percent, roughly 40 kilometers [25 miles] above Earth’s high northern latitudes, according to Cora Randall of University of Colorado at Boulder and 10 colleagues in Canada, Norway, Sweden, and the United States. Two natural processes were responsible, they say.
"This decline was completely unexpected," Randall said. "The findings point out a critical need to better understand the processes occurring in the ozone layer." Randall, a researcher at the university’s Laboratory for Atmospheric and Space Physics, is lead author of a paper on the subject scheduled for publication 2 March in Geophysical Research Letters. She and her international team studied data from seven different satellites, concluding that both the Sun and stratospheric weather were responsible for the ozone declines.
Winds in the upper part of a massive winter low-pressure system, which confines air over the Arctic region and is known as the polar stratospheric vortex, sped up in February and March 2004 to become the strongest on record, she said. The spinning vortex allowed the nitrogen gases, thought to have formed at least 30 kilometers [20 miles] above the stratosphere as a result of chemical reactions triggered by energetic particles from the Sun, to descend more easily into the stratosphere.
Harvey Leifert | AGU
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