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LARGEST-EVER
OZONE HOLE OBSERVED OVER ANTARCTICA
The
largest ozone hole ever recorded, roughly three times the
size of the U.S., was detected September 6, 2000 by NASA's
Total Ozone Mapping Spectrometer.
For
high resolution image, click here.
A NASA spectrometer has detected an Antarctic ozone "hole"
(what scientists call an "ozone depletion area") that is three
times larger than the entire land mass of the United States
- the largest such area ever observed.
The "hole" expanded to a record size of approximately 11 million
square miles (28.3 million square kilometers) on Sept. 3,
2000. The previous record was approximately 10.5 million square
miles (27.2 million square km) on Sept. 19, 1998.
The ozone hole's size currently has stabilized, but the low
levels in its interior continue to fall. The lowest readings
in the ozone hole are typically observed in late September
or early October each year.
"These observations reinforce concerns about the frailty of
Earth's ozone layer. Although production of ozone-destroying
gases has been curtailed under international agreements, concentrations
of the gases in the stratosphere are only now reaching their
peak. Due to their long persistence in the atmosphere, it
will be many decades before the ozone hole is no longer an
annual occurrence," said Dr. Michael J. Kurylo, manager of
the Upper Atmosphere Research Program, NASA Headquarters,
Washington, DC.
Ozone
molecules, made up of three atoms of oxygen, comprise a thin
layer of the atmosphere that absorbs harmful ultraviolet radiation
from the Sun. Most atmospheric ozone is found between approximately
six miles (9.5 km) and 18 miles (29 km) above the Earth's
surface.
Scientists continuing to investigate this enormous hole are
somewhat surprised by its size. The reasons behind the dimensions
involve both early-spring conditions, and an extremely intense
Antarctic vortex. The Antarctic vortex is an upper-altitude
stratospheric air current that sweeps around the Antarctic
continent, confining the Antarctic ozone hole.
"Variations in the size of the ozone hole and of ozone depletion
accompanying it from one year to the next are not unexpected,"
said Dr. Jack Kaye, Office of Earth Sciences Research Director,
NASA Headquarters. "At this point we can only wait to see
how the ozone hole will evolve in the coming few months and
see how the year's hole compares in all respects to those
of previous years."
"Discoveries like these demonstrate the value of our long-term
commitment to providing key observations to the scientific
community," said Dr. Ghassem Asrar, Associate Administrator
for NASA's Office of Earth Sciences at Headquarters. "We will
soon launch QuickTOMS and Aura, two spacecraft that will continue
to gather these important data."
The measurements released today were obtained using the Total
Ozone Mapping Spectrometer (TOMS) instrument aboard NASA's
Earth Probe (TOMS-EP) satellite. NASA instruments have been
measuring Antarctic ozone levels since the early 1970s. Since
the discovery of the ozone "hole" in 1985, TOMS has been a
key instrument for monitoring ozone levels over the Earth.
TOMS-EP
and other ozone-measurement programs are important parts of
a global environmental effort of NASA's Earth Science enterprise,
a long-term research program designed to study Earth's land,
oceans, atmosphere, ice and life as a total integrated system.
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