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Elvia H. Thompson
Headquarters, Washington March 28, 2003
(Phone: 202/358-1696)

Alan Buis
Jet Propulsion Laboratory (JPL), Pasadena, Calif.
(Phone: 818/354-0474)

RELEASE: 03-125

NASA FINDS WIDE ANNUAL FLUCTUATIONS IN ARCTIC OZONE LOSS

     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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