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The Ozone Hole
2000
Environment
Canada Southern Hemisphere Ozone Map September 3,2000
British Antarctic Survey summary-The
2000 ozone hole reached its greatest extent in early September at 28.4 million
square kilometres and was the largest ever-recorded ozone hole. It reached this
maximum extent unusually early, as the hole is normally largest in late
September. Minimum ozone values were measured in early October and were amongst
the lowest on record. The edge of the ozone hole passed over the tip of South
America and the Falkland Islands for significant periods between October 6 and
24. The hole also closed in unusually early and the event was essentially over
by early December. This early closure of the hole is probably linked with the
QBO/ENSO and in retrospect was to be expected.
Satellite imagery gives a global
perspective on the ozone hole. TOVS and TOMS currently have significantly
different calibrations, with TOVS reading some 30 DU higher than TOMS. TOMS
values are close to ground-based values. Stratospheric clouds were sighted
from Vernadsky, Rothera and Halley. A mini ozone hole, with central values below
200 DU, periodically formed to the east of the Antarctic Peninsula over the
Weddell Sea during July. This mini ozone hole probably formed due to processing
of ozone through PSCs, which are far enough north to be sunlit. The feature was
particularly marked on July 10 and again on July 20.
Ozone values over the Arctic are normally
at their lowest in September and 2000 was no exception as can be see from the
TOMS images. Although the values were low, they were low because of
stratospheric dynamics and not chemistry. The temperature in the Arctic ozone
layer was above –55 °C, far too warm for stratospheric clouds to form. Hence
there was no chemical depletion taking place and no ozone hole above the Arctic.
In mid October there were regions of low ozone over Siberia. Stratospheric
temperatures in this area were generally above –65 °C, so again these
features had a dynamic, not chemical origin. The temperature of the Arctic
stratosphere did fall below the threshold for PSC formation at times in small
regions during 2001 January and February. These regions developed ozone values
lower than elsewhere in the Arctic, and in mid February values below 250 DU were
recorded by TOMS over a small area of northwest Europe. Ozone values are
currently high over most northern temperate and polar latitudes.
7
September 2000- Japan's
Meteorological Agency on Tuesday September 5 said the size of the hole in
the ozone layer over the Antarctic is at its largest ever -- more than twice the
size of the surface of the Antarctic -- due to low temperatures beneath the
stratosphere. The hole was estimated to be 28.4 million square kilometers on
Sunday, larger than the previous worst record of 27 million sq. km in 1998,
agency officials said.
The
ozone layer does a remarkable job
of absorbing ultraviolet radiation. In the absence of this gaseous shield
in the stratosphere, the harmful radiation has a perfect portal through
which to strike Earth. This
biologically damaging, high-energy radiation can cause skin cancer, injure
eyes, harm the immune system, and upset the fragile balance of an entire
ecosystem.
Environment
Canada Southern Hemisphere Ozone Map September 3,2000
NASA Press Release
LARGEST-EVER
OZONE HOLE OBSERVED OVER ANTARCTICA
9September
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 11.5 million square
miles (30.3 million square kilometers) on Sept. 3, 2000. The previous record was
approximately 10.5 million square miles (28.2 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.
August
2000
September
2000
October
2000
November
2000
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