NASA
CONFIRMS ARCTIC OZONE DEPLETION TRIGGER NASA
researchers using 22 years of satellite-derived data have confirmed a theory that
the strength of "long waves," bands of atmospheric energy that circle
the earth, regulate the temperatures in the upper atmosphere of the Arctic, and
play a role in controlling ozone losses in the stratosphere. These findings will
also help scientists predict stratospheric ozone loss in the future. These
long waves affect the atmospheric circulation in the Arctic 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 long waves that enter the stratosphere, which then
thins the ozone layer. Just
as the weather at the Earth's surface varies a lot from one year to the next,
so can the weather in the stratosphere. For instance, here were some years like
1984, in which it didn't get cold enough in the Arctic stratosphere for significant
ozone loss to occur. "During that year, we saw stronger and more frequent
waves around the world, that acted as the fuel to a heat engine in the Arctic,
and kept the polar stratosphere from becoming cold enough for great ozone losses,"
said Paul Newman, lead author of the study and an atmospheric scientist at NASA's
Goddard Space Flight Center, in Greenbelt, Md. "Other
years, like 1997, weaker, and less frequent waves reduced the effectiveness of
the Arctic heat engine and cooled the stratosphere, making conditions just right
for ozone destruction," Newman said. The paper appears in the September 16
issue of Journal of Geophysical Research-Atmospheres. The
temperature of the lower level of the stratosphere over the poles is also controlled
by the change in seasons from winter to spring, and by gases such as ozone, water
vapor and carbon dioxide. A
long wave or planetary wave is like a band of energy, thousands of miles in length
that flows eastward in the middle latitudes of the upper atmosphere, and 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. These
long waves move up from the lower atmosphere (troposphere) into the stratosphere,
where they dissipate. When these waves break up in the upper atmosphere they produce
a warming of the polar region. So, when more waves are present to break apart,
the stratosphere becomes warmer. When fewer waves rise up and dissipate, the stratosphere
cools, and the more ozone loss occurs. Weaker
"long waves" over the course of the Northern Hemisphere's winter generate
colder Arctic upper air temperatures during spring. By knowing the cause of colder
temperatures, scientists can better predict what will happen to the ozone layer.
The
temperature of the polar lower stratosphere during March is the key in understanding
polar ozone losses - and the temperature at that time is usually driven by the
strength and duration of "planetary waves" spreading into the stratosphere. This
discovery provides a key test of climate models that are used to predict polar
ozone levels. "This then lends itself to adjusting climate models, and increasing
their accuracy, which means scientists will have a better way to predict climate
change in the future," Newman said. The
stratosphere is an atmospheric layer about 6 to 30 miles above the Earth's surface
where the ozone layer is found. The ozone layer prevents the sun's harmful ultra-violet
radiation from reaching the Earth's surface. Ultra-violet radiation is a primary
cause of skin cancer. Without upper-level ozone, life on Earth would be non-existent. The
research used temperature measurements of the stratosphere from the Upper Atmospheric
Research Satellite (UARS).
Arctic
Ozone Layer animation - Bands of energy thousands of miles in length flow
eastward in the upper atmosphere, affecting the atmospheric circulation in the
Arctic by either strengthening it resulting in warmer temperatures, or by weakening
it for cooling temperatures. Warmer temperatures allow ozone to exist while colder
temperatures cause a chemical reaction eventually depleting the ozone layer. An
unconfirmed theory is that greenhouse gases may be responsible for decreasing
the number of long waves that enter the stratosphere, which thins the ozone layer.
While
not the 'hole' that exists over the Antarctic, the depleted region of ozone in
the Arctic reached its lowest point in 1999 to an altitude of nearly 60,000 feet.
This view of the Arctic ozone was created with data obtained by the Total Ozone
Mapping Spectrometer (TOMS) instrument aboard NASA's Earth Probe spacecraft. SUPER:
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