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The Ozone Hole
2001
British Antarctic Survey summary-In
2001 the ozone hole reached an area of over 25 million square kilometres at its
maximum in September, and lasted until the summer solstice. Once the hole had
gone, ozone levels at Halley remained some 12% below the normal for the time of
year. The temperature at the level of the ozone layer (100 hPa temperature) also
substantially below the normal for the time of year.
Some early Halley observations using
moonlight gave total ozone values around 220 DU at the beginning of August, a
depletion of about 25%. In September values dropped from around 180 DU at the
beginning of the month at around 2 DU per day. From the equinox to late October
values were around 125 DU, which is 60% below the normal. The minimum daily mean
value recorded this year was 116 DU. Mean values rose to around 270 DU in
November, but dropped back to around 240 DU in mid December. They then rose to
reach 300 DU (12% below the normal) by early January.
The 100 hPa temperature at Halley (at
-45°C) remains significantly below the normal (-40°C). It rose rapidly from
around -80°C in late October to reach -46°C at the solstice. There was a
standstill at -60°C in late November and early December. It was a few degrees
below the normal for most of the first half of 2001, except for a short period
between mid March and the end of April.
Satellite imagery gives a global
perspective on the ozone hole. Our 2001/2002 Antarctic ozone hole movie is
produced from TOMS images.
A low ozone event with central values
below 200 DU occurred on the edge of the sunlit polar vortex between June 15 and
June 28. The hole developed and reached over 25 million square kilometres in mid
September. By early December it had shrunk to 7 million square kilometres, with
minimum values still below 200 DU. It disappeared at the solstice. Ozone values
in the temperate high ozone belt are now declining after the spring maximum. The
edge of the ozone hole passed over the tip of South America, the Falkland
Islands and South Georgia during the period from October 15 to 26.
National Oceanic
and Atmospheric Administration summary-Very
low ozone values were observed over Antarctica again in 2001. Ozone depletion of
10 percent to more than 40 percent was observed over Antarctica compared to
total ozone amounts observed in the early 1980's. Vertical soundings over the
South Pole during late September and early October 2001 again showed complete
destruction of ozone at altitudes between 15 and 20 km. Lower stratosphere
temperatures in the winter and spring of 2001 over the Antarctic region were
below average values, and were sufficiently low for ozone production of polar
stratospheric clouds within the polar vortex. The ozone hole area and the PSC
area were again among the largest of all previous years. For the year 2001, the
ozone hole and Southern Hemisphere polar vortex persisted into December, again
among the longest duration of years since 1982.
Observations of
chloroflourocarbons and of stratospheric hydrogen chloride support the view that
international actions are reducing the use and release of ozone depleting
substances . However, chemicals already in the atmosphere are expected to
continue to deplete ozone for many decades to come. Further, changing
atmospheric conditions that modulate ozone can complicate the task of detecting
the start of ozone layer recovery. The eruption of the Pinatubo volcano provided
an example of such a complication in the 1990s. Based on an analysis of 10 years
of South Pole ozone vertical profile measurements, estimated that recovery in
the Antarctic ozone hole may be detected as early as the coming decade.
Indicators include: 1) an end to springtime ozone depletion at 22-24 km, 2)
12-20 km mid-September column ozone loss rate of less than 3 DU per day, and 3)
a 12-20 km ozone column of more than 70 DU on September 15. However, an
intriguing aspect of recent observations of the Antarctic stratosphere is the
apparent trend towards a later breakup of the vortex. A full explanation of such
meteorological anomalies is not yet available. Continued monitoring and
measurements, including total ozone and its vertical profile, are essential to
achieving the understanding needed to identify ozone recovery.
http://www.cpc.ncep.noaa.gov/products/stratosphere/winter_bulletins/sh_01/index.html
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Ozone Measurement
1 Dobson Unit (DU) is defined to be 0.01 mm thickness
at STP (standard temperature and pressure). Ozone layer thickness is expressed
in terms of Dobson units, which measure what its physical thickness would be if
compressed in the Earth's atmosphere.
In
those terms, it's very thin indeed. A
normal range is 300 to 500 Dobson units, which translates to an eighth of an
inch-basically two stacked pennies.
In space, it's best not to envision the
ozone layer as a distinct, measurable band. Instead, think of it in terms of
parts per million concentrations in the stratosphere (the layer six to 30 miles
above the Earth's surface).
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NASA Earth Probe TOMS
Images
Earth Probe TOMS is
currently the only NASA spacecraft on orbit specializing in ozone retrieval.
Comparison ozone hole
year 2000 development and growth with ozone hole year 2001
August
2001
September
2001
October
2001
November
2001
December
2001
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Environment
Canada
Southern
Hemisphere Ozone Maps
Comparison ozone hole
year 2000 development and growth with ozone hole year 2001
June
2001
July
2001
August
2001
September
2001
October
2001
November
2001
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