NASA Finds Wide Annual Fluctuations In Arctic Ozone Loss
Elvia H. Thompson
NASA Jet Propulsion Laboratory (JPL), Pasadena, Calif.
|March 28, 2003
Ozone depletion over Earth's Arctic region varies widely from year
to year in its amount, timing and pattern of loss. That's the conclusion
of a research team using data from the Microwave Limb Sounder (MLS)
on NASA's Upper Atmosphere Research Satellite.
The findings, published in the current issue of the Journal of Geophysical
Research, provide the first consistent, three-dimensional picture
of ozone loss during multiple Arctic winters. The findings confirm
previous Arctic ozone loss estimate variations.
"This work provides a consistent picture of how Arctic ozone
loss varies between winters," said lead researcher Dr. Gloria
Manney, a senior research scientist with NASA's Jet Propulsion Laboratory,
Pasadena, Calif. "Scientists will have a better understanding
of current Arctic ozone conditions and be better able to predict
variations in the future."
Manney said NASA's unique vantage point in space provides data needed
by policy makers. "They need accurate data to show whether
current regulations on ozone-depleting substances are having the
desired effect," she said. "In this way, NASA is providing
a vital piece of the puzzle needed to understand this global phenomenon."
Ozone is a form of oxygen that shields life on Earth from harmful
ultraviolet radiation. Earth's stratospheric ozone layer is thinning
around the world outside of the tropics. This thinning is a result
of chlorofluorocarbons produced by industrial processes, which form
reactive compounds like chlorine monoxide in the stratosphere during
winter. To date, ozone loss has been most pronounced over Antarctica,
where colder conditions encourage greater ozone loss and result
in ozone "hole."
Higher temperatures and other differences in atmospheric conditions
in the Arctic have thus far prevented similarly large depletions.
Nevertheless, as Manney and her colleagues validated in 1994, widespread
Arctic ozone loss also occurs, and scientists are eager to understand
it better, since formation of Arctic ozone "hole" could
negatively affect populations in Earth's far northern latitudes.
Many uncertainties remain regarding ozone depletion. Scientists
want to know what is causing ozone decreases in Earth's mid latitudes.
They also wish to assess effects of climate change on future ozone
loss, especially in the northern hemisphere high latitudes.
In the new study, Manney's team reanalyzed MLS observations during
seven Arctic winters (1991 - 2000) to estimate chemical ozone loss.
To yield accurate estimates, the team developed a model to account
for naturally occurring ozone variations resulting from atmospheric
transport processes such as wind variability. Their results show
large year-to-year variability in the amount, timing and patterns
of Arctic ozone loss. Ozone depletion was observed in the Arctic
vortex each year except 1998, when temperatures were too high for
chemical ozone destruction. This vortex is a band of strong winds
encircling the North Pole in winter like a giant whirlpool. Inside
the vortex, temperatures are low and ozone-destroying chemical are
confined. Ozone loss was most rapid near the vortex edge, with the
biggest losses in 1993 and 1996. The greatest loses occurred in
the months of February and March.
The variability in the size, location and duration of the Arctic
vortex is driven by meteorological conditions. High mountains and
land-sea boundaries in the northern hemisphere interact with wind
variations to generate vast atmospheric undulations that displace
air as they travel around Earth. These waves form in the troposphere
(the lowest atmospheric layer), where they produce our winter storms,
and propagate upward, depositing their energy in the stratosphere.
The energy from these waves warms the stratosphere, suppressing
formation of polar stratospheric clouds necessary for ozone destruction.
Arctic ozone loss tends to be greatest in years when these wave
motions are unusually weak.
NASA's MLS experiments measure naturally occurring microwave thermal
emissions from the limb of Earth's atmosphere to remotely sense
vertical profiles of selected atmospheric gases, temperature and
pressure. These data are unique in their ability to show the three-dimensional
evolution of ozone loss over time. The Microwave Limb Sounder on
the Upper Atmosphere Research Satellite was the first such experiment
in space. A next-generation MLS, developed and built at JPL for
the Aura mission of NASA's Earth Observing System, is scheduled
for launch in 2004. That instrument will provide simultaneous observations
of ozone and one or more long-lived trace gases, substantially advancing
future studies of ozone loss. The California Institute of Technology
in Pasadena manages JPL for NASA.
For more information about the Microwave Limb Sounder, see: http://mls.jpl.nasa.gov
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