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:
