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Upper Stratospheric winds increase ozone-depleting gases

By: American Geophysical Union
Published: Sep 28, 2006 at 07:28

Winds circling high above the
Arctic have a much greater impact on upper stratospheric ozone levels than
scientists had previously thought, according to a new report. In March 2006, the
winds allowed near-record amounts of ozone-destroying gases, collectively known
as nitrogen oxides or NOx, to descend some 50 kilometers [30 miles] from the
mesosphere to the top of Earth’s stratosphere.

NOx, is a generic term for a
group of highly reactive gases, all of which contain nitrogen and oxygen in
varying amounts, especially nitric oxide and nitrogen dioxide. Because NOx
destroys ozone, which heats up the stratosphere by absorbing ultraviolet
radiation, the naturally occurring gases could trigger atmospheric changes that
could have unanticipated climate consequences, according to Cora Randall of the
University of Colorado at Boulder, lead author of the study.

In February 2006, winds in the
polar upper stratospheric vortex, a massive winter low-pressure system that
confines air over the Arctic region, sped up to rival the strongest such winds
on record, said Randall. The only time more nitrogen oxides were observed in the
upper stratosphere was in the winter of 2003-2004, when huge solar storms
bombarded the region with energetic particles, triggering up to a 60 percent
reduction in ozone molecules, said Randall.

“We knew strong winds would lead
to more NOx in the stratosphere if there were solar storms, but seeing that much
NOx come down into the stratosphere when the Sun was essentially quiet was
amazing,” Randall said. Her paper on the subject was published 27 September in
Geophysical Research Letters, published by the American Geophysical Union.
Researchers from the University of Waterloo in Ontario, Canada, and the
University of Michigan, as well as the University of Colorado participated in
the study.

The upper stratosphere lies
several kilometers [miles] higher than the ozone hole of the lower stratosphere,
which is caused by man-made gases, including chlorine and bromine, which gobble
up ozone molecules. Because there is significantly less ozone in the upper
stratosphere, the ozone-destroying nitrogen oxide gases are unlikely to cause
immediate health threats, such as increases in skin cancer, Randall said.

The destructive NOx gases,
created above the stratosphere when sunlight or energetic particles break apart
oxygen and nitrogen molecules, appear to be important players in controlling the
temperature of Earth’s middle atmosphere, according to Randall. “If
human-induced climate change leads to changes in the strength of the polar
vortex, which is what scientists predict, we’ll likely see changes in the amount
of NOx descending into the stratosphere,” she said. “If that happens, more
stratospheric NOx might become the rule rather than the exception.”

“The atmosphere is part of a
coupled system, and what affects one layer of the atmosphere can influence other
layers in surprising ways,” Randall said. “We will only be able to predict and
understand the consequences of human activities if we study the entire system as
a whole, and not just in parts.”

The 2006 increases of NOx in the
upper stratosphere occurred over the Arctic and the northern areas of North
America and Europe, according to the paper’s authors. The research team used
data from Canadian and United States satellites, including the Canadian
Atmospheric Chemistry Experiment.

The work was funded by NASA and
the Canadian Space Agency.