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WAVES
IN THE ATMOSPHERE BATTER
SOUTH POLE, SHRINK
2002 OZONE HOLE
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A
greater number of large "planetary sized waves"
in the atmosphere that move from the lower atmosphere into
the upper atmosphere were responsible for the smaller Antarctic
ozone hole this fall, according to NASA researchers. The September
2002 ozone hole was half the size it was in 2000. However,
scientists say that these large-scale weather patterns in
the Earth's atmosphere are not an indication that the ozone
layer is recovering.
Paul
Newman, a lead researcher on ozone at NASA's Goddard Space
Flight Center, Greenbelt, Md., said that large scale weather
patterns have an affect on ozone when large "planetary
sized waves" move up into ozone layer. If the waves are
more frequent and stronger as they move from the surface to
the upper atmosphere, they warm the upper air. Such weather
phenomena are known as "stratospheric warmings."
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The
stratosphere is an atmospheric layer about 6 to 30 miles above
the Earth's surface where the ozone layer is found. Ozone
breaks down more easily with colder temperatures. A long wave
or planetary wave is a weather system that circles the world.
It resembles a series of ocean waves with ridges (the high
points) and troughs (the low points).
Typically,
at any given time, there are between one and three of these
waves looping around the Earth. With more or stronger atmospheric
waves, temperatures warm aloft. The warmer the upper air around
the "polar vortex" or rotating column of winds that
reach into the upper atmosphere where the protective ozone
layer is, the less ozone is depleted.
Newman
said, "The Southern Hemisphere large scale weather systems
are similar to the semi-permanent area of high pressure, which
brought sunshine and dry conditions over much of the eastern
United States during the 2002 summer." These large Southern
Hemisphere weather systems generated more frequent and stronger
planetary waves that caused a series of stratospheric warmings
during the Southern winter. Scientists aren't exactly certain
why that happened. What they are certain of is that these
waves warmed the upper atmosphere at the poles, and cut ozone
loss.
"2002
was a year of record setting planetary waves in both frequency
and strength," Newman said. As a result, the total area
of the ozone hole over the Antarctic was just over 15 million
square kilometers (km) (5.8 million square miles) in late
September. The ozone hole was virtually gone by late-October,
one of its earliest disappearances since 1988.
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Comparatively,
the 2001 Antarctic ozone hole was over 26.5 million km squared
(10.2 million square miles), larger than the entire area of
North America including the U.S., Canada and Mexico combined.
In the year 2000, it was approximately 30 million km squared
(11.5 million square miles). The last time the ozone hole
was as small as it is this year was 1988, and that was also
most likely due to large scale surface weather systems.
"This
is an entirely different factor from chemicals in the atmosphere
that affects the protective ozone layer," Newman said.
The Montreal Protocol regulated chlorofluorocarbons (CFCs)
in 1987, because of their destructive affect on the ozone
layer. However, CFCs still linger in the upper atmosphere.
"The main reason why the ozone hole is smaller this year
than last is simply because of higher temperatures from these
waves. Decreases of CFCs are only causing the ozone hole to
decrease by about 1% per year." It could be an entirely
different story next year, if similar weather systems are
not in place.
The
waves affect the atmospheric circulation in the Antarctic
by strengthening it and warming temperatures, or weakening
it and cooling temperatures. Colder temperatures cause polar
clouds to form, which lead to chemical reactions that affect
the chemical form of chlorine in the stratosphere. In certain
chemical forms, chlorine can deplete the ozone layer. One
theory is that greenhouse gases may be responsible for decreasing
the number of waves that enter the stratosphere, which then
thins the ozone layer.
The
temperature of the polar lower stratosphere during September
is a key in understanding the size of the ozone hole - and
the temperature at that time is usually driven by the strength
and duration of "planetary waves" spreading into
the stratosphere.
Newman
stressed that the smaller ozone hole this fall is not an indication
that the ozone layer is recovering. He said it's simply due
to a change in global weather patterns for this year, and
next year it may likely be as large as it was last year.
This
poster, "The 2002 Antarctic Ozone Hole," will be
presented at the American Geophysical Union Fall 2002 Meeting
in the Moscone Convention Center, in Hall D on Friday, December
6, 2002 at 8:30 a.m. (Pacific Time) Session # A51B-0044.
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