Solar Storms, Arctic Winds Thin Northern Ozone Layer

BOULDER, Colorado, March 3, 2005 (ENS) - The sun and stratospheric weather in 2004 caused the largest decline in the upper ozone layer ever recorded over the far Northern Hemisphere, according to new research by U.S., Canadian, and European scientists published Wednesday. A form of oxygen, this ozone layer protects life on Earth from the harmful effects of the Sun's ultraviolet radiation.

"This decline was completely unexpected," said research associate Cora Randall of the Laboratory for Atmospheric and Space Physics at University of Colorado-Boulder, chief author of a paper on the subject in the March 2 online issue of "Geophysical Research Letters."

Based on data from seven different satellites, the scientists discovered that nitrogen oxide and nitrogen dioxide (NOx) gases in the upper stratosphere climbed to the highest levels in at least two decades in spring 2004.

Ozone levels are decreasing in the stratosphere over the North Pole. The dark blue in this image shows the areas with lower ozone levels. (Image courtesy NASA)

The increases led to ozone reductions of up to 60 percent roughly 25 miles in altitude above Earth's high northern latitudes, said Randall.

Winds in the upper part of a massive winter low pressure system that confines air over the Arctic region, 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 two nitrogen gases to descend more easily into the stratosphere. The NOx increases are important because they are major players in the stratospheric ozone destruction process, said Randall.

The scientists believe these nitrogen gases were formed at least 20 miles above the stratosphere as a result of chemical reactions triggered by energetic particles from the sun.

Randall said, "This study demonstrates that scientists searching for signs of ozone recovery need to factor in the atmospheric effects of energetic particles, something they do not now do."

"No one predicted the dramatic loss of ozone in the upper stratosphere of the northern hemisphere in the spring of 2004," she said. "That we can still be surprised illustrates the difficulties in separating atmospheric effects due to natural and human-induced causes.

One of the satellite-mounted instruments that supplied data to this study, Canada's OSIRIS (Optical Spectrograph and InfraRed Imager System) measures the concentration of ozone depleting pollutants. (Photo courtesy Canadian Space Agency)

Severe ozone losses also can occur during winter and spring in the stratosphere at about 12 miles in altitude, driven by very cold temperatures, they said.

"The findings point out a critical need to better understand the processes occurring in the ozone layer," said Randall.

Thinning of the ozone layer in the Southern Hemisphere is better known than Arctic ozone loss, but in 2004 a relatively warm Antarctic winter kept the thinning of the protective ozone layer over Antarctica, known as the ozone hole, slightly smaller than in 2003.

The stratospheric ozone layer has thinned in high latitudes of both the Northern and Southern Hemispheres in recent decades, due to reactions involving chlorofluorocarbons and other industrial gases.

Production and consumption of compounds that deplete ozone in the stratosphere - chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and methyl chloroform - were phased out by 2000 under the Montreal Protocol for Substances that Deplete the Ozone Layer, a 1987 international agreement to which the United States is a party.

Co-authors on the paper include researchers from CU-Boulder; the National Oceanic and Atmospheric Administration; the National Aeronautics and Space Administration; the Harvard-Smithsonian Center for Astrophysics in Cambridge; Hampton University and GATS Inc. of Hampton, Virginia; York University in Toronto; Chalmers University of Technology in Sweden; and the Norwegian Institute for Air Research.

Layers of the atmosphere are diagrammed here.