Hole Remains Over Antarctica
By Steve Hall
October 23, 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.
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.
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.
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.
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
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.
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.
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.
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
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.
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