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South Pole, Shrink 2002 Ozone Hole
December 6, 2002
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.”
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.
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.
For more information and images:
http://www.gsfc.nasa.gov/topstory/20021206ozonehole.html.
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Contact:
Robert J. Gutro
Goddard Spc Flt Ctr, Greenbelt, Md.
ANTARCTIC OZONE HOLE SPLITS IN TWO![]()
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NASA September 30, 2002 UNUSUALLY
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Ozone Measurement
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Earth Probe TOMS is Comparison
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The total ozone maps are Maps of deviations represent total ozone deviations from the Over areas with poor data coverage adjustments are made
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