Most concerns about ozone depletion involve the lower portions of the stratosphere—about 7 miles (11 kilometers) above Earth's surface—where pollutants creeping up from below can destroy ozone.
(Related news: "Old Fridges, Cars Slow Ozone Hole Recovery, Scientists Say" [December 2005].)
But higher in the stratosphere UV light interacts with ozone to heat up the thin air 30 miles (50 kilometers) above Earth—near the boundary where the stratosphere meets the next layer, the mesosphere.
NOx gases are created in the mesosphere when it is bombarded by energetic particles from outer space that are drawn to the Poles by Earth's magnetic field.
Normally NOx stays high up in the mesosphere, where it is quickly broken down by sunlight.
But strong, high-altitude winds can create a vortex that draws the gases down into the upper stratosphere.
"As long as you get those winds, you're going to get NOx coming down, and it's going to destroy ozone," said Randall, whose study was published in the September 27 issue of the journal Geophysical Research Letters.
Before last year's event, the only time on record when more NOx descended from the mesosphere was in the winter of 2003-04.
Solar storms that season created so much NOx above the Arctic that the gases triggered a 60 percent reduction in the region's ozone molecules.
Changes in the amount of ozone alter the amount of heating in the upper atmosphere, potentially affecting global climate, Randall says.
In particular, less ozone means a cooler stratosphere at the Poles.
That creates a larger temperature difference between the Poles and the Equator, which in turn could lead to changes in upper stratospheric wind patterns, Randall says.
While last year's winds were probably a natural effect, global warming could affect the winds in the future.
But scientists are still trying to understand how the many layers of the atmosphere affect each other and thus impact climate.
"We only have one atmosphere," Randall said. "I wish I could tell people how [this] is going to affect people on the ground, but there are a lot of connections that still have to be made."
Other climate scientists are intrigued by Randall's findings.
"I think this is an interesting result and the authors are to be congratulated," Lon Hood, of the University of Arizona's Lunar and Planetary Laboratory in Tucson, wrote in an email.
Hood notes that similar effects probably occur at the South Pole.
"These downward-transport events occur more commonly in the Southern Hemisphere, where the polar vortex is usually stronger than it is in the Northern Hemisphere," he said.
Drew Shindell, of the NASA Goddard Institute for Space Studies in New York City, added that any effect on climate—while "plausible"—would occur "through a long chain of complicated processes."
Studies like this, he says, are important, because they reveal new feedback mechanisms that could affect global climate.
"It's a region of the atmosphere that most people haven't thought of a lot," he said.
"We don't know exactly what climate is going to do up there, but it will certainly change something."
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