Record-setting
Ozone Hole
Antarctica's ozone hole has
expanded to cover an area three times larger than the
United States.
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Sept.
8, 2000 -- 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 28.3 million square
kilometers on Sept. 3, 2000. The previous record was
approximately 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.
Above: Readers can monitor
ozone concentrations for themselves thanks to near-real-time
global maps published at NASA's Total
Ozone Mapping Spectrometer web site. In this map,
completed on Sept 6, 2000, the Antarctic ozone hole is
prominent as a purple region surrounding the south
pole. The column density of ozone, expressed in Dobson
Units (DU), above any point on the map is
represented by its color. Dark gray denotes low
concentrations and red denotes high concentrations. [more
information about this image]
"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 9.5
km and 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 in the southern hemisphere,
and an extremely intense Antarctic vortex. The
Antarctic vortex is an upper-altitude stratospheric
air current that sweeps around the Antarctic
continent, confining the ozone hole.
Above: This image from the
TOMS web site
shows how the size and depth of the 2000 Antarctic
ozone hole (red line) compare with 1999's (black line)
and with the mean values from 1979 to 1992. The grey
shaded region indicates the range of values observed
during the interval 1979 to 1992. [more
information]
"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.
Related Links:
Science
@ NASA Headlines!
TOMS
Web Site -- data and information about the
Total Ozone Mapping Spectrometer (TOMS) instrument
aboard NASA's Earth Probe (TOMS-EP) satellite.
Recent
Ozone Hole Measurements -- quicktime movies
and still images from NASA
Ozone
and the Atmosphere -- a tutorial on Earth's
present day atmosphere, ozone creation and
depletion, and the complex interactions under study
by scientists worldwide
Stratospheric
Ozone: An Electronic Textbook -- a
comprehensive tutorial about the chemistry and
dynamics of the ozone layer
