The Ozone Hole 2000

http://ozonewatch.gsfc.nasa.gov

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. 

NASA Press
Release

NOAA 2000-072
FOR IMMEDIATE RELEASE
Contact: Barbara McGehan
10/5/00

OZONE HOLE EARLIER,
BUT NOT DEEPER IN 2000

Scientists from the
Commerce Department’s National Oceanic and Atmospheric Administration report
that measurements of this year’s ozone hole at the South Pole show that ozone
depletion occurred earlier there, but did not reach the very lowest values of
some recent years. The ozone hole, a region of ozone depletion over Antarctica,
is the result of complex chemical and meteorological processes that occur in the
stratosphere.

Using instrumented
balloons to take vertical profiles of the ozone at the South Pole, researchers
from NOAA’s Climate Monitoring and Diagnostics Laboratory located in Boulder,
Colorado, reported that the September decline in ozone occurred about six days
earlier than in any previous year and, as observed in other recent years, ozone
was totally destroyed between about 9 and 13 miles altitude. Total column ozone
reached the minimum reading of 98 Dobson units on September 29, compared to 90
Dobson units in 1999. The record low of 88 Dobson units was observed in 1993. 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 Dobson
unit reading is around 275.

Another measure of
the severity of the ozone hole is its total area. Estimates of the area of the
ozone hole are made at NOAA’s Climate Prediction Center by analysis of
measurements made by the Solar Backscatter Ultraviolet (SBUV/2) instruments on
NOAA’s Polar-orbiting Operational Environmental Satellites operated by NOAA’s
National Environmental Satellite, Data, and Information Service. Satellite data
show the ozone hole area was over 27 million square kilometers for three days in
early September, peaking at 28.5 million square kilometers. “This is the largest
geographical size on record and comparable to the area of North America”, said
Lawrence Flynn, a physical scientist at NESDIS. The ozone hole is defined as the
size of the region with total ozone below 220 Dobson units. NASA released
similar measurements using the Total Ozone Mapping Spectrometer (TOMS) aboard
NASA’s Earth Probe (TOMS-EP) satellite. NOAA and NASA satellites have been
measuring Antarctic ozone levels for almost 30 years. Continued monitoring by
satellite instruments over the next two months will establish how long-lived the
current year’s ozone hole will be.

“Even though the
geographical size of the ozone hole was the largest on record and the ozone
depleted earlier than ever, the severity of the ozone depletion within the hole
reached about the same levels as the past few years,” said David Hofmann,
director of CMDL. “Year-to-year fluctuations in the geographical size of the
ozone hole and the timing of the ozone reduction are believed to be related to
meteorological factors such as temperature and winds, rather than further
increases in ozone-destroying chemicals in the atmosphere,” Hofmann said.

Each spring when the
sun rises over Antarctica, chemical reactions involving chlorine and bromine
from man-made CFCs (chlororfluorocarbons) and bromine-containing compounds,
occur in the stratosphere destroying ozone and causing the “ozone hole.” The
global ozone layer has also deteriorated since 1980 but not to the extent that
is observed each spring in Antarctica. An international assessment of the status
of the global ozone layer, produced by hundreds of scientists for the World
Meteorological Organization and the United Nations Environmental Program in
1998, indicated that the amount of chlorine in the stratosphere from CFCs should
soon be reaching a maximum due to regulations on emissions as dictated by the
Montreal Protocol on substances that deplete the ozone layer and subsequent
amendments.

The amount of
chlorine in the atmosphere at the surface of the Earth was measured by CMDL to
have begun declining already in 1994. 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.

Hofmann says that
“since chlorine in the atmosphere has reached nearly constant levels, annual
variations in temperature, which affect the rate of the chemical reactions, will
be the dominant factor in determining differences in the magnitude of the ozone
hole. 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.”

Note to editors:
Balloonborne ozone profiles and an animation of the profiles from the South Pole
is available at: http://www.cmdl.noaa.gov

For color images of
the ozone hole and stratospheric temperature
information as observed by NOAA satellites:
http://www.cpc.ncep.noaa.gov/products/stratosphere/polar/polar.html

Daily monitoring of
the SBUV/2 measurements is provided at:
http://psbsgi2.nesdis.noaa.gov/PSB/Ozone/monitor

WMO Antarctic
Ozone Summary for 2000

Meteorological
conditions

The minimum
temperatures from July through October were somewhat lower than in the
last decade. Therefore, the area with temperatures low enough to produce
PSCs during August and September somewhat exceeded the previous years in
the last decade. This was not the case for October, and PSC activity ended
by November 1, which is earlier than usual. From July to September the
vortex was one of the largest in recent years although in mid October the
area decreased rapidly when compared to recent years.

Ozone
observations

The
meteorological conditions during winter set the stage for an earlier than
usual development of the Antarctic ozone hole. Moreover, the maximum area
of the ozone hole was the largest on record (about 27 million km2) and
appeared on 13 September, which was earlier than usual. Also in September,
the monthly average ozone hole area exceeded all previous years. As with
the PSC and vortex areas, a very rapid decrease in the size of the ozone
hole occurred in October, and by late October the ozone hole was the
smallest of the past decade. By mid November the ozone hole had
disappeared. While this ozone hole was very deep with an average September
OMD comparable to the previous three years, it was one of the shallowest
during October and November. The abrupt change in depth and size was also
seen in the high latitude monthly zonal averages. The area with ozone
values with more than 50% deviation from pre-ozone hole norms was
unusually large in early September and continued into early October. Most
of the Antarctic GAW ground-based stations also measured their lowest
daily values ever. From September to early October the ozone hole was
elongated, becoming more circular by mid October.

Conditions
over the populated regions

The southern
tip of South America experienced average ozone values about 30% below
pre-ozone hole norms during the second half of September and the second
half of October. Furthermore, the station in Ushuaia frequently measured
very low ozone values, including a total of 14 days under the ozone hole,
a record for this location. Highly depleted air extended several times
towards South America during September and October. On 12 October Ushuaia
reported a record breaking ozone value more than 50% below pre-ozone hole
norms. The UV index for this day was above 11, a value comparable to UV
exposure in the Tropics. However, beginning in late October Ushuaia
observed near normal values. In late August, New Zealand experienced ozone
values about 25% below pre-ozone hole norms for four days, and in early
September they had values up to 20% below norms for three days. Column
ozone over Tasmania was observed to be 20% below norms on one day in early
September.