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.
NOAA, NASA REPORT
2001 OZONE HOLE SIMILAR IN SIZE TO HOLES OF
PAST THREE YEARS
Scientists See Leveling off of Hole Size, Predict Slow Recovery
October 16, 2001 — NOAA and NASA
scientists report that satellite data show the area of the Antarctic ozone hole
peaked at about 26 million square kilometers (about 10 million square miles),
making this year’s ozone hole the same size as North America, and similar in
size to those of the past three years.
Over the past several years the
annual ozone hole over Antarctica has remained roughly the same in both area and
minimum total column ozone amount. “This is consistent with human-produced
chlorine compounds that destroy ozone reaching their peak concentrations in the
atmosphere, leveling off, and now beginning a very slow decline,” said NOAA
scientist Samuel Oltmans. In the near future (barring unusual events such as
explosive volcanic eruptions) the severity of the ozone hole will likely remain
similar to what has been seen in recent years with year-to-year differences
associated with meteorological variability. Over the longer term (30-50 years)
the severity of the ozone hole in Antarctica is expected to decrease as chlorine
levels in the atmosphere decline.
The total area of the ozone hole
is one measure of its severity. The ozone hole area is defined as the size of
the region with total ozone below 220 Dobson units. A Dobson unit is a unit of
measurement that describes the thickness of the ozone layer in a column directly
above the location being measured. Prior to the springtime period in Antarctica,
when ozone depletion occurs, the normal ozone reading is around 275 Dobson
units. “Last year the ozone hole was of record size, but it formed very early
and then collapsed quickly,” said NASA scientist R.D. McPeters. “This year the
hole was about 10 percent smaller.”
Data from NOAA’s polar-orbiting
operational environmental satellites and estimates of the area made by NASA
scientists using measurements from the Total Ozone Mapping Spectrometer (EPTOMS)
aboard NASA’s Earth Probe satellite give similar sizes.
Each spring when the sun rises over Antarctica, chemical reactions involving
chlorine and bromine from man-made CFCs (chlorofluorocarbons) and
bromine-containing compounds occur in the stratosphere and destroy ozone,
causing the “ozone hole.” Measurements of this year’s ozone hole made at the
South Pole and above the Antarctic show that atmospheric ozone depletion reached
the low levels typical of the past 10 years.
Using instrumented balloons to
make ozone profile measurements at the South Pole, researchers from NOAA
reported that the September decline in ozone was similar to recent years with
almost all of the ozone in the 15 – 20 kilometer (9-12 mile) altitude region
destroyed.” Total column ozone over the South Pole reached a minimum reading of
100 Dobson units on Sept. 28, 2001, compared to a minimum of 98 Dobson units in
2000,” said Bryan Johnson, a scientist with NOAA’s Climate Monitoring and
Diagnostics Laboratory in Boulder, Colo. The record low of 88 Dobson units was
observed in 1993.
“The severity of the ozone
depletion within the hole reached about the same levels as the past few years
and the highly depleted region filled about three-fourths of the Antarctic polar
vortex,” said Jim Miller, a scientist with NOAA’s Climate Prediction Center in
Camp Springs, Md.” This year the vortex has been more stable and somewhat colder
than average.” Year-to-year fluctuations in the geographical size of the polar
vortex and the size of the region with low temperatures will alter the size of
the ozone hole over the next decade during the period that levels of
ozone-destroying chemicals in the atmosphere begin a slow decline. The amount of
chlorine in the stratosphere from CFCs has reached a maximum due to regulations
on emissions as dictated by the Montreal Protocol on substances that deplete the
ozone layer and subsequent amendments.
NOAA and NASA scientists report
that this year’s ozone hole is not cause for alarm, and is within the bounds of
what was expected. The thinning of the ozone layer is a matter of concern
because the ozone layer protects the Earth from the harmful effects of the sun’s
ultraviolet radiation, which affects life on Earth and contributes to skin
cancer and cataracts in humans. Total recovery of the ozone hole back to levels
observed before 1980 will take at least 50 years, and expected changes in
climate, including a cooler stratosphere, could cause a delay in the recovery of
the ozone layer.
NASA and NOAA satellite
instruments have been measuring Antarctic ozone levels for more than 20 years.
Continued monitoring by satellite instruments over the next two months will
establish how long-lived the current year’s ozone hole will be, and a summary
report will be issued by NOAA in December.
NOAA is dedicated to enhancing
economic security and national safety through the prediction and research of
weather and climate-related events and providing environmental stewardship of
our nation’s coastal and marine resources.
Relevant Web Sites
NOAA’s Ozone Online
NOAA’s Climate Monitoring and
Diagnostics Laboratory
Media Contact:
Patricia Viets, NOAA Satellite Service, (301) 457-5005
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).
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
