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2007 Antarctic
Ozone Hole off to a Robust Start Over South Pole
NOAA Global Monitoring Division -
ESRL-GMD 11th Sep, 2007 04:57:42 PM PST
NOAA Earth System Research
Laboratory balloon-borne ozonesonde measurements from the South Pole show that
the seasonal ozone hole has begun with September soundings following a similar
trajectory to those of the past 15 years toward large ozone losses by the end of
the month. In late July, stratospheric air temperatures of -95 C were some of
the coldest measured over the past 20 years and have remained colder than normal
in the 20-24 km altitude layer, providing excellent conditions for the formation
of polar stratospheric clouds, the precursors to reactive chlorine
photochemistry and catalytic ozone destruction. Despite the early indications of
larger ozone depletion this year at South Pole, it is difficult to predict if
near record minimums will be observed as they were in 2006 when total column
ozone dropped to 93 DU on October 9. September will be the most critical month
for the stratospheric ozone destruction as sunlight spreads over the entire
continent and ozone destruction increases to a rate of 3-4 DU per day over South
Pole.
Background: Balloonborne
ozonesonde measurements have been conducted by NOAA/ESRL from the South Pole
Amundsen-Scott station since 1986 to track the development and recession of the
annual austral springtime Antarctic Ozone Hole. Balloon profiles have shown the
primary ozone depletion region occurs within the altitude range of 14 to 24 km.
Ground based Dobson spectrophotometer measurements began in 1963 using direct
sun and moon light to measure total column ozone. (To see the August 28 lunar
eclipse at South Pole go to the web site listed below). The year to year
variability in Antarctic ozone depletion is in response to colder than normal
recent Antarctic stratospheric temperatures and a persistent polar vortex. The
cold, stable conditions produce vast areas where polar stratospheric clouds form
and process the chlorine and bromine species into active forms that destroy
ozone beginning at polar sunrise.
Significance: Ozone plays an
important role by shielding humans and other life from harmful ultraviolet light
from the sun. Emissions of chemicals, such as chlorofluorocarbons (CFSs), over
the last decades have led to depletion of the stratospheric ozone layer.
Although ozone destroying halocarbons are decreasing in the atmosphere in
response to controls put into effect by the Montréal Protocol, there are
still sufficient concentrations of these compounds available to completely
remove ozone in a large portion of the Antarctic stratosphere.
More information: http://www.esrl.noaa.gov/gmd/dv/spo_oz/
Contact information Name: Bryan
Johnson Tel: (303) 497-6842 Bryan.Johnson@noa.agov
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