From: LARRY KLAES (email@example.com)
Date: Fri Dec 06 2002 - 09:15:01 PST
----- Original Message -----
From: Mark Hess
Sent: Friday, December 06, 2002 11:58 AM
To: News Media list.serv
Subject: WAVES IN THE ATMOSPHERE BATTER SOUTH POLE, SHRINK 2002 OZONE HOLE
Cynthia M. O'Carroll December 6, 2002
Goddard Space Flight Center, Greenbelt, Md.
Robert J. Gutro
AGU Press Room
WAVES IN THE ATMOSPHERE BATTER SOUTH POLE, SHRINK 2002 OZONE HOLE
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
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
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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