NOAA, NASA:
Significant ozone hole remains over Antarctica
October 20, 2011
The Antarctic ozone hole, which
yawns wide every Southern Hemisphere spring, reached its annual peak on
September 12, stretching 10.05 million square miles, the ninth largest on
record. Above the South Pole, the ozone hole reached its deepest point of the
season on October 9 when total ozone readings dropped to 102 Dobson units, tied
for the 10th lowest in the 26-year record.
Ozone
levels in the atmosphere above the South Pole dropped to a seasonal low of 102
Dobson Units Oct. 9, tied for the 10th lowest in the 26-year record. The ozone
layer helps protect the planet’s surface from harmful ultraviolet radiation.
Every year, an ozone hole forms above the Antarctic for several weeks, because
of environmental conditions and the presence of ozone-depleting chemicals.
The ozone layer helps protect the
planet’s surface from harmful ultraviolet radiation. NOAA and NASA use
balloon-borne instruments, ground instruments, and satellites to monitor the
annual South Pole ozone hole, global levels of ozone in the stratosphere, and
the manmade chemicals that contribute to ozone depletion.
“The upper part of the
atmosphere over the South Pole was colder than average this season and that cold
air is one of the key ingredients for ozone destruction,” said James Butler,
director of NOAA’s Global Monitoring Division in Boulder, Colo. Other key
ingredients are ozone-depleting chemicals that remain in the atmosphere and ice
crystals on which ozone-depleting chemical reactions take place.
“Even though it was relatively
large, the size of this year's ozone hole was within the range we'd expect given
the levels of manmade, ozone-depleting chemicals that continue to persist,"
said Paul Newman, chief atmospheric scientist at NASA's Goddard Space Flight
Center.
Levels of most ozone-depleting
chemicals are slowly declining due to international action, but many have long
lifetimes, remaining in the atmosphere for decades. Scientists around the world
are looking for evidence that the ozone layer is beginning to heal, but this
year’s data from Antarctica do not hint at a turnaround.
In August and September (spring in Antarctica), the sun begins rising again
after several months of darkness. Circumpolar winds keep cold air trapped above
the continent, and sunlight-sparked reactions involving ice clouds and manmade
chemicals begin eating away at the ozone. Most years, the conditions for ozone
depletion ease by early December, and the seasonal hole closes.
Levels of most ozone-depleting
chemicals in the atmosphere have been gradually declining since an international
treaty to protect the ozone layer, the 1987 Montreal Protocol, was signed. That
international treaty caused the phase out of ozone-depleting chemicals, then
used widely in refrigeration, as solvents and in aerosol spray cans.
Global atmospheric models predict
that stratospheric ozone could recover by the middle of this century, but the
ozone hole in the Antarctic will likely persist one to two decades beyond that,
according to the latest analysis by the World Meteorological Organization, the 2010
Ozone Assessment, with co-authors from NOAA and NASA.
Researchers do not expect a
smooth, steady recovery of Antarctic ozone, because of natural ups and downs in
temperatures and other factors that affect depletion, noted NOAA ESRL scientist
Bryan Johnson. Johnson helped co-author a recent NOAA paper that concluded it
could take another decade to begin discerning changes in the rates of ozone
depletion.
Johnson is part of the NOAA team
tracks ozone depletion around the globe and at the South Pole with measurements
made from the ground, in the atmosphere itself and by satellite. Johnson’s
“ozonesonde” group has been using balloons to loft instruments 18 miles into
the atmosphere for 26 years to collect detailed profiles of ozone levels from
the surface up. The team also measures ozone with satellite and ground-based
instruments.
This November marks the 50th
anniversary of the start of total ozone column measurements by the NOAA Dobson
spectrophotometer instrument at South Pole station. Ground-based ozone column
measurements started nearly two decades before the yearly Antarctic ozone hole
began forming, therefore helping researchers to recognize this unusual change of
the ozone layer.
NASA measures ozone in the
stratosphere with the Ozone Monitoring Instrument (OMI) aboard the Aura
satellite. OMI continues a NASA legacy of monitoring the ozone layer from space
that dates back to 1972 and the launch of the Nimbus-4 satellite.
A new satellite scheduled to
launch this month, the NPP satellite, features a new ozone-monitoring
instrument, the Ozone Mapping and Profiler Suite, which will provide more
detailed daily, global ozone measurements than ever before to continue the task
of observing the ozone layer's gradual recovery. The NPP satellite is part of
Joint Polar Satellite System, a program of NOAA, NASA and the Department of
Defense (formerly known as the NPOESS Preparatory Project). It is scheduled to
launch October 27 from Vandenberg Air Force Base in California.
NOAA’s mission is to understand
and predict changes in the Earth's environment, from the depths of the ocean to
the surface of the sun, and to conserve and manage our coastal and marine
resources.
Goddard Release No. 11-069 (co-issued as HQ Release No.
11-357)
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