- Angell, J.K. OAR/Air Resources Laboratory
- Flynn, L.E. NESDIS/Center for Satellite Research and Applications
- Gelman, M.E. NWS/Climate Prediction Center
- Hofmann, D. OAR/Earth System Research Laboratory
- Long, C.S. NWS/Climate Prediction Center
- Miller, A.J. NWS/Climate Prediction Center
- Oltmans, S. OAR/Earth System Research Laboratory
- Zhou, S. RS Information Systems, Inc.
Concerns of global ozone depletion (e.g. WMO, 1999) have led to major international
programs to monitor and explain the observed ozone variations in the stratosphere. In
response to these, as well as other long-term climate concerns, NOAA has established
routine monitoring programs utilizing both ground-based and satellite measurement
techniques (OFCM, 1988).
Selected indicators of stratospheric climate are presented in each Summary from
information contributed by NOAA personnel. A Summary for the Northern Hemisphere is issued
each April, and for the Southern Hemisphere, each December. These Summaries are available
on the World- Wide-Web, at the site
with location: products/stratosphere/winter_bulletins.
Further information may be obtained from Melvyn E. Gelman
W/NP52, RM 806, WWB
NOAA Climate Prediction Center
5200 Auth Road
Camp Springs, MD 20746-4304
Telephone: (301) 763-8071, ext. 7558
Fax: (301) 763-8125
Extensive ozone depletion was again observed
over Antarctica during the Southern Hemisphere
winter of 2006, with widespread total ozone anomalies of 45 percent or more below the 1979-1986
base period. The area covered by extremely low total ozone values of less than 220 Dobson Units,
defined as the Antarctic “ozone hole” area, in September reached maximum size of greater than 27
million square kilometers, the second largest of any previous year, as measured by the SBUV(/2) since 1979.
The average size during October
and November of 18 million square Km, was larger than any previous year. Vertical profiles of
ozone amounts, measured by balloonsondes over the South Pole, showed near complete destruction
of ozone in the 13-21 km region over a prolonged period of time, with minimum values lower than
those seen during other recent years. At the South Pole, the minimum total ozone value of 93 Dobson
Units was observed on 9 October 2006, when the center of the ozone hole was nearby. Lower
stratosphere temperatures over the Antarctic region in the winter of 2006 were again well below -78
C, and were sufficiently low for polar stratospheric cloud formation, promoting chemical ozone loss.
The size of the area of very low temperatures in 2006 was among the largest of any in recent years.
The date (Nov 6) at which temperatures rose above -78C in the lower stratosphere was the latest
observed since 1979 and was conducive to a prolonged presence of PSCs and the chemical
destruction of ozone into early November. The polar vortex remained intack until early December
when it and the remains of the ozone hole rapidly dissipated as the polar circulation changed over into
its summer pattern.
I. DATA RESOURCES
The data used for this report are listed below. This combination of complementary data,
from different platforms and sensors, provides a strong capability to monitor global ozone
Method of Observation
||Balloon - Radiosonde
We have used total column ozone data from the NASA Nimbus-7 SBUV instrument from 1979
through February1985; NOAA-9 SBUV/2 from March 1985 to December 1988; NOAA-11 SBUV/2
from January 1989 to December 1993; NOAA-9 SBUV/2 from January 1994 to December 1995;
NOAA-14 SBUV/2 from January 1996 to June 1998; NOAA-11 SBUV/2 from July 1998 to
September 2000; and NOAA-16 SBUV/2 from October 2000 to November 2006. Solar Backscatter
Ultra-Violet (SBUV) data are not available at polar latitudes during winter darkness.
Maps of monthly average Southern Hemisphere SBUV/2 total ozone for August, September, October, and November 2006 are
shown in Figures 1a, 2a,
3a, and 4a, respectively.
“Ozone hole” values (defined as total ozone values less than 220 DU) appear over most of Antarctica slightly displaced
from the South Pole, and the highest total ozone column amounts are found over the Pacific Ocean, poleward of Australia.
Figures 1b, 2b,
3b, and 4b
show the percent difference between the monthly mean total ozone for each month, August-November 2006, and
the respective average (1979-86) monthly means (Nagatani et al., 1988).
Extreme negative anomalies in total ozone of greater than 45 percent are shown
in Figures 1b, 2b,
3b, and 4b, for August, September, October, and November over almost all of Antarctica and adjacent ocean areas, reaching
toward southern Argentina. Also, of note is that the region of high ozone values outside of the ozone
hole region was also below normal this year (see 30S to 60S in Figs. 1b, 2b, 3b, and 4b).
Figure 5a compares, for each year since 1979,
the average daily ozone hole area from October
through November. The growth in the October-November ozone hole in the years from the 1980s
through the 1990s is quite apparent. From a very small area in 1982, October-November average
values increased dramatically to a maximum in 1998 and 1999 of 16.4 million square kilometers.
The October-November 2006 average size of the ozone hole was 18.0 million square kilometers,
largest on record.Figures
5b,, 5c, and
show the individual monthly average ozone hole size for,
respectively, August, September, October, and November, 1980-2006. The size increased from
August to September 2006, decreased from September to October, and substantially diminished in
November. The size of the ozone hole for August, October and November 2006 was largest on
record, and among the 4 largest on record for September.
Figure 6 displays monthly average anomaly values (percent) of zonal mean total ozone, as a function
of latitude (80N to 80 S) and time (January 1979 to November 2006). The anomalies are derived
relative to each month's 1979-2006 average. Long-term ozone changes may be readily seen in the
polar regions, where ozone values were substantially lower in the 1990s than in the 1980s. Largest
anomalies are shown for the polar regions in each hemisphere in winter-spring months, with positive
anomalies of more than 10 percent in the earlier years changing to negative anomalies of greater than
10 percent for the 1990s. For 2006 the lowest ozone anomalies over south polar latitudes were larger
than for other recent years.
The center of the ozone hole and associated lowest ozone, and polar vortex are often located close to the
South Pole. Figure 7 shows a time series during 2006 of total ozone, measured over the South
Pole using balloon-borne ozone instruments, compared with other selected years. Low ozone values
were measured in September 2006, with lowest values evident at the end of September and early
October, when the center of the ozone hole was closest to the South Pole. Total ozone values rose in
November and December, when the ozone hole diminished and was displaced from the South Pole.
On 9 October (Figure 8) a total column ozone amount of 93 DU was
measured at the South Pole,
the minimum value for the year 2006. The sequence of profiles in Figure 8 show near complete
destruction of ozone between 13 and 21 km for a prolonged period of days, associated with classic
ozone hole conditions. A contributing factor to these conditions was that the polar vortex and the
ozone hole were quite stable and centered over the south polar region for much of the winter/spring
season. The vertical time series in Figure 9 of ozone profiles at the South Pole during 2006 also
shows the time sequence of dramatic decreases in ozone between 13 and 21 km in September and
October. Extremely low values of ozone associated with ozone hole conditions continued in
October, and remained anomalously low through November as the lower stratosphere remained cold
during this time period.
One of the longest records of ozone measurements in Antarctica is the total column ozone amount obtained with
the Dobson spectrophotometer at South Pole Station. Consistent observations can be obtained beginning on
October 15 of each year when sufficient sunlight is available for these optical measurements that use the
sun as a light source. This record of average October 15-31 column amounts shown in
Figure 10 indicates declines that accelerated in the
1980s and reached consistently low values from 1993-1999. Since 2000 there has been greater
variability in this average as a result of variable meteorological conditions. For 2005 and 2006,
total ozone values were very low.
Ozone amounts in the lower stratosphere are closely coupled to temperatures through dynamics and photochemistry.
Extremely low stratospheric temperatures (lower than -78 C) over the Antarctic region contribute to depletion of
ozone, in that low temperatures lead to the presence of polar stratospheric clouds (PSCs). PSCs enhance the
production and lifetime of reactive chlorine, leading to ozone depletion (WMO, 1999). Daily minimum
temperatures at 50 hPa (approximately 19 km) over the polar region, averaged from 65S to 90S are shown in
Figure 11. For May through October 2006, minimum temperatures in the south polar region were well
below -78 C remaining close to mean conditions. These minimum temperatures remained cold
making them the record lows observed in August through November. The date (Nov 6)
at which temperatures rose above -78C in the lower stratosphere was the latest observed since
1979 and was conducive to a prolonged presence of PSCs and the chemical destruction of ozone
into early November. Temperatures in the winter and spring of 2006 were lower than in 2005.
The record setting temperature and stability of the 2006 polar vortex are consistent with the
devolpment of the 2006 ozone hole; larger than observed in any previous year for most of October and November.
Figure 12 shows monthly average temperature anomalies at 50 hPa for three latitude regions,
25S-25N, 65S-25S, and 90S-65S. 50 hPa temperatures and total ozone amounts are strongly correlated as most of the
ozone in the vertical column is between 70 and 30 hPa. For the south polar region, 2006 temperatures were mostly lower,
and for the last few months of 2006, substantially lower than the long-term average. Negative
temperature anomalies also predominated over the middle latitudes of the Southern Hemisphere and
over tropical latitudes. Both the tropical and middle latitudes of the Southern Hemisphere continue
the tendency toward lower temperatures after 1993 relative to higher temperatures in earlier years.
Figure 13 presents time series of the size of the ozone hole, the size of the polar vortex, and the size
of the polar area where lower stratosphere temperatures were below -78 C (polar stratospheric cloud,
PSC area). The daily 2006 values are shown, along with the extreme and average daily values for the
most recent 10 years. The size of the ozone hole, polar vortex and PSC area was often larger than in
any previous year.
Figure 14 illustrates the direct relationship between the persistence of the ozone hole and the
persistence of the Antarctic polar vortex. In years when the winter polar vortex persisted later in the
season, the duration into the spring season of the ozone hole also tended to be extended. For the year
2006, the persistence of the Southern Hemisphere polar vortex in the lower stratosphere extended
longer than any previous year. The persistence of the ozone hole to the beginning of December was
the sixth longest on record.
III. CONCLUDING REMARKS
Very low ozone values were again observed over Antarctica in the winter of 2006. Ozone depletion
of more than 45 percent was observed over Antarctica, compared to total ozone amounts observed in
the early 1980's. Vertical soundings over the South Pole during August, September and October
2006 again showed strongest destruction of ozone at altitudes between 13 and 21 km. Lower
stratosphere temperatures in the winter of 2006 over the Antarctic region were lower than in 2005
and near record levels. Associated with this, the ozone hole was larger than in other years. The
ozone hole in 2006 diminished in size and depth along with warming stratospheric conditions in
October, and by early December, total ozone over Antarctica had increased to levels above ozone
The stability of the stratospheric polar vortex structure, which kept it generally centered over the
South Pole, and the very persistent, anomalously cold temperatures in the presence of halogen
levels that remain at high levels (though no longer at their highest levels) were the prime
contributors to the record setting depletion.
Observations of chloroflourocarbons and of stratospheric hydrogen chloride support the view that
international actions are reducing the use and release of ozone depleting substances (WMO, 1999;
Anderson et al., 2000). However, chemicals already in the atmosphere are expected to continue to
impact the ozone amount for many decades to come. The Antarctic ozone hole is expected to continue for decades.
Antarctic ozone abundances are projected to return to pre-1980 levels around 2060-2075, roughly 10-25
years later than estimated in the 2002 Assessment. The projection of this later return is
primarily due to a better representation of the time evolution of ozone-depleting gases in the
polar regions. In the next two decades, the Antarctic ozone hole is not expected to improve
significantly.(WMO, 2006) Further, changing conditions (i.e.
meteorological, solar, and volcanic aerosols) 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, Hofmann et al., (1997) 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. An intriguing
aspect of recent observations of the Antarctic stratosphere had been the apparent trend towards a later
breakup of the vortex in years since 1990, relative to the 1980s. The size and duration and size of
the 2006 ozone hole is attributed in part to meteorological conditions. 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
Anderson, J., J. M. Russell III, S. Solomon, and L. E. Deaver, 2000: Halogen Occultation Experiment
confirmation of stratospheric chlorine decreases in accordance with the Montreal Protocol,
J. Geophys. Res., 105, 4483-4490.
Hofmann, D.J., S.J. Oltmans, J.M. Harris, B.J. Johnson, and J.A. Lathrop, 1997: Ten
years of ozonesonde measurements at the south pole: implications for recovery of
springtime Antarctic ozone. J. Geophys. Res., 102, 8931-8943.
Miller, A.J., R.M. Nagatani, L.E. Flynn, S. Kondragunta, E. Beach, R. Stolarsky,
R. McPeters, P.K. Bhartia, M. Deland, C.H. Jackman, D.J. Wuebbles, K.O. Putten, and R.P. Cebula, 2002,
A cohesive total ozone data set from SBUV/(2) satellite system, J.Geophys. Res., 107(0),doi:10.1029/200,D000853.
Nagatani, R.N., A.J. Miller, K.W. Johnson, and M.E. Gelman, 1988: An eight year
climatology of meteorological and SBUV ozone data, NOAA Technical Report NWS 40, 125 pp.
OFCM, 1988: National Plan for Stratospheric Monitoring 1988-1997. FCM-P17-1988. Federal
Coordinator for Meteorological Services and Supporting Research, U.S. Dept. Commerce,
Planet, W. G., J. H. Lienesch, A. J. Miller, R. Nagatani, R, D. McPeters, E.
Hilsenrath, R. P. Cebula, M. T. DeLand, C. G. Wellemeyer, and K. M. Horvath, 1994:
Northern hemisphere total ozone values from 1989-1993 determined with the NOAA-11 Solar
Backscatter Ultraviolet (SBUV/2) instrument. Geophys. Res. Lett., 21,
WMO, 1999: Scientific assessment of ozone depletion: 1998. World Meteorological
Organization Global Ozone Research and Monitoring Project - Report No. 44.
WMO, 2006: Scientific assessment of ozone depletion: 2006. World Meteorological
Organization Global Ozone Research and Monitoring Project.
VI. Web Pages of Interest