- Butler, A.H. NWS/Climate Prediction Center
- Flynn, L.E. NESDIS/Center for Satellite Research and Applications
- Johnson, B.J. OAR/Earth System Research Laboratory
- Long, C.S. NWS/Climate Prediction Center
- Oltmans, S.J. OAR/Earth System Research Laboratory
- Rosenlof, K.H. OAR/Air Resources Laboratory
- Zhou, S. Wyle Information Systems, Inc.
Concerns about 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
after each April, and for the Southern Hemisphere, after each December. These Summaries are available
on the World-Wide-Web, at the site
Further information may be obtained from Craig S Long
W/NP52, RM 806, WWB
NOAA Climate Prediction Center
5200 Auth Road
Camp Springs, MD 20746-4304
Telephone: (301) 763-8071, ext. 7557
Fax: (301) 763-8125
E-mail: Craig.Long at noaa.gov
The 2010 ozone hole had two remarkable features: it was one
of the latest forming ozone holes observed and it was one of the longest lasting ozone holes observed. Ozone
depletion typically begins in late July and early August with an observed ozone hole size of 10 million square
kilometers by mid-August. The “ozone hole” is defined as the area in the polar latitudes where the total column
ozone amounts are less than 220 Dobson Units (DU). This year the ozone hole was not observed via satellite
measurements (i.e. total column ozone amounts below 220 Dobson Units) until the last week in August. It grew
to a maximum size of 20.6 million sq km on September 26, 2010. From this point on the SH polar vortex and the
ozone hole decreased in size at a much slower rate than previous years. The SH polar circulation was minimally
affected by poleward wave propagation during the austral spring time, remaining zonally symmetric. The absence
of substantial poleward heat flux extended the transition from winter to summer circulation patterns over the
South Pole in the lower stratosphere. This year’s ozone hole and polar vortex remained almost intact well into
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 Solar Backscatter
UltraViolet (SBUV) instrument from 1979 through 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 December 1998; NOAA-11 SBUV/2 from January 1999 to December
2000; NOAA-16 SBUV/2 from January 2001 to December 2005; NOAA-17 from January 2006 to December 2008; and NOAA-18 from January 2009 to present.
Solar-backscatter ultraviolet measurements are not available at polar latitudes during winter darkness.
Ozone Hole Size and Longevity
Figure 1 presents the temporal evolution of (a) the size of the 2010
ozone hole, (b) the area of the Southern Hemisphere (SH) polar vortex in the lower stratosphere, and (c) the
area extent of temperatures in the SH polar region low enough (-78° C) to support the creation of Polar
Stratospheric Clouds (PSC). Figure 1a shows that depletion of the total column ozone amount at or below 220 DU
was delayed in 2010 compared to the previous ten years. Total column amounts from the Solar Backscatter
Ultraviolet-2 (SBUV/2) instrument on board the NOAA 17, 18, and 19 polar orbiting environmental space craft
were used in determining the total column ozone amounts over the SH high latitudes. There is sufficient
sunlight in early August to cause ozone depletion at the outer edges of the SH polar vortex if PSCs exists.
Figure 1b shows that the size of the SH polar vortex in July, August and September was actually larger than
the past 10 year mean. The edge of the SH polar vortex is determined by the location of the -32 potential
vorticity units (PVU) isoline on the 450K isentropic surface. Figure 1c shows that even though the SH polar
vortex was quite large: the area of temperatures cold enough to form PSCs was extraordinarily small from
mid-July through all of August. This implies that the temperature of the air inside the vortex was not very
cold, thus limiting the area of temperatures cold enough to form PSCs. Since, climatologically, the coldest
temperatures are located closest to the South Pole (SP), additional time was needed for sunlight to reach
these higher latitudes to start the heterogeneous chemical reactions to deplete ozone in the vertical column.
By the beginning of September, there was sufficient sunlight to illuminate the entire South Polar region and
rapid ozone depletion ensued. Figure 1a shows that ozone depletion rapidly occurred in September and the peak
ozone hole size of 20.6 million square kilometers (msk) was reached on September 26th.
By the second week in October temperatures in the lower
stratosphere over the South Polar region had risen above -78°C (Figure 5 ) and consequently very little
additional ozone was depleted by photochemical reactions. But because the barrier between the ozone depleted
polar vortex region and the ozone rich region outside of the vortex stays strong until the spring circulation
reversal, the area of depleted ozone inside the polar vortex exists well into November or December.
Figure 1b shows that the SH polar vortex for 2010 was as large or nearly as large as any of the past
10 years from May through December. The continuance of the SH polar vortex allowed the area of ozone
depleted air to also exist into mid-December.
The maximum ozone hole size for 2010 of 20.6 msk was small relative to the previous 20 years of mature ozone
holes (see Figure 2 ). Since 1990, the only ozone holes smaller than 2010 were observed in 2002 (18.0 msk)
and 2004 (19.6 msk). As discussed above, much of the reason for this can be explained by the small size of
the area available for PSCs to form. Figure 3 shows the mean PSC area for all Septembers from 1979 to present.
The 2010 mean September PSC area of 15.2 msk is the 8th smallest of the 32 year record. In the last decade,
2002 and 2004, the years with relatively small maximum ozone hole sizes, also had small September PSC areas.
The reason why the PSC area for 2010 was small can be explained by Figure 4. This figure shows the
time series of eddy heat flux towards the South Pole (SP) (negative values indicate southward heat flux).
A large pulse of eddy heat flux occurred in mid- June, again in mid-July, and again in early September.
These pulses caused temperatures to rapidly rise in the South Polar region thus deceasing the area of very
cold temperatures and reducing the area of PSC formation.
Figure 5 shows the time series of the lowest temperature for the 65°-90°S region at
50 hPa for the past two years. The minimum temperature is shown because when it is below the -78°C threshold,
PSCs can form. The late-autumn/early-winter period (May through early-July) show temperatures that were
below average. But after the mid-July heat flux pulse, the temperatures warmed up to the long-term average
and stayed there or warmer until October when the temperatures became colder than average.
After the early September pulse, Figure 4 shows that the poleward eddy heat flux
activity fell below the 1979-2009 mean for the rest of September and all of October and November.
This extended period of quiescence contributed substantially to the longevity of the SH polar vortex
in the lower stratosphere and the extended life of the 2010 ozone hole.
Figure 6 shows the 50 hPa polar temperature anomalies for the
“pre ozone hole peak” period (July-August-September (JAS)) and “post ozone hole peak’ period
(September-October-November (SON)) for all years since 1979. The JAS polar average temperature for
2010 is above average. Most years since 1998 have been colder than average, which is correlated with
earlier onsets of ozone depletion and larger ozone hole sizes. The small ozone hole size years of 2002,
1988 and 1986 vividly show up as very warm JAS years. In contrast, the SON monthly average temperatures
for 2010 are cooler than average. Each one of the years with cooler than average SON temperatures are also
years with vortex and ozone hole longevity.
As mentioned above, the longevity of the ozone hole and the polar vortex are highly correlated.
Figure 7 shows the last detectable date of all the ozone holes since 1979
versus the last detectable date of the SH polar vortex on the 450K isentropic surface. The last date
that the ozone hole is detectable (< 2.5 msk) always precedes the last date that the SH polar vortex is
detectable (< 5.0 msk). The minimum “detectable” areas represent the error limits for each of the
parameters. Years in which the polar vortex and the ozone hole are long lasting are in the upper right
side of the plot, and years in which the vortex breaks up early are in the lower left corner. The values for
2010 are plotted in red and are only rivaled as the longest lasting ozone hole and polar vortex dates by
those of 2008.
Southern Hemisphere Winter/Spring Ozone Depiction
The monthly mean total column ozone analyses for August, September, October, and November and their
anomalies from the “pre-ozone hole” period of 1979-1986 are presented in
Figure 8 and Figure 9, respectively.
The monthly mean total column ozone analysis for August
(Figure 8a ) shows that the NOAA-18 observations had extended at least to 68° S, far enough south to
observe any ozone depletion occurring at the edge of the polar vortex. The total column ozone analyses
for September, October, and November
(Figure 8b, 8c, and 8d, respectively)
show that the ozone depleted region is fairly circular and centered close to the SP.
The August and September anomalies from the 1979-86 “pre-ozone hole” time period
( Figure 9a and Figure 9b)
show that the crescent region of high ozone amounts southeast of New Zealand had larger total
column ozone amounts while the rest the 30°-60°S zone and latitudes poleward had significantly
less ozone (> 30% less). The anomaly patterns for October and November are more zonally symmetric
than the previous two months and centered over the SP. In the tropics there are large positive
anomalies (>20% more) of total column ozone. This is in response to the current phase of the
quasi-biennial oscillation (QBO) and its influence on the poleward transport of ozone out of the
tropics towards the pole.
Figure 10 shows the zonal mean total column ozone anomalies
from 1979 through 2010. The anomalies are derived by taking the 1979-2010 monthly zonal means from the
monthly total column ozone amounts. In the equatorial region a definite QBO pattern is present. In the
mid-latitudes, the total column ozone anomalies consistently are out of phase with the total column ozone
anomalies in the tropics, i.e. when there are high ozone anomalies in the tropics, there are low total
ozone anomalies in the mid-latitudes, and vice-versa. Figure 11
shows the equatorial stratospheric zonal mean zonal wind values and is representative of the QBO. When
there is westerly shear associated with the QBO (i.e. westerlies over easterlies) the Brewer-Dobson
circulation is weaker and less ozone is transported toward the winter pole, thus accounting for the
positive anomalies in the tropics and negative anomalies in the SH mid and high latitudes.
Conditions over the South Pole
Ozonesonde observations from the South Pole also indicate that for the entire SH high latitude region,
temperatures beginning in July through early September became warmer than previous years
(Figure 12 ). The total column ozone amounts from mid-August through
October were higher than previous years (Figure 13 ) as was the layer
ozone amount between12-20 km (where the greatest ozone depletion occurs)
(Figure 14 ). Individual ozonesonde soundings during the lowest total column
ozone period (September 30-October 11, 2010) are plotted in Figure 15 .
The day with the lowest total column ozone amount occurred on September 30 with 122 DU observed.
The day with the lowest 12-20 km layer ozone amount was on October 11. Although there was complete
ozone destruction at some altitudes, none of the soundings show complete ozone destruction
between 12-20 km. A period of lower total and layer ozone amounts persisted through November
following these dates agreeing with the persistence of the polar vortex and the ozone hole.
The 2010 ozone hole has contrasting characteristics for the SH winter and spring months. The winter
months (July and August) were warmer than average due to several poleward eddy heat flux pulses that
occurred in June, July and early September. These pulses caused the temperatures in the entire stratosphere
to be warmer than average. These warmer temperatures were unfavorable for Polar Stratospheric Clouds. As a
result, additional weeks were required before sun light illuminated the colder regions and initiated the
heterogeneous ozone destruction chemistry. The peak ozone hole size for 2010 of 20.6 million square
kilometers was smaller than in most recent years. From mid-September onward, there was very little poleward
eddy heat flux. As a result, the SH polar vortex remained very stable as did the area of the ozone hole. The
slow progression of the transition from winter to summer circulation patterns meant that the lower
stratospheric polar vortex did not break up until late-December. As a result, the vanishing dates of the
ozone hole and the SH polar vortex were later than any previous year.
IV. What is to be expected
Observations of chlorofluorocarbons 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 atmospheric ozone amounts
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, 2007). 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 22 years of South Pole ozone vertical profile measurements,
Hofmann et al., (2009) suggested that, according to indicators such as the September ozone loss rate at
14-21 km and ozone loss at the upper limits of the ozone hole (22-24 km), the beginning of recovery of the
Antarctic Ozone Hole had not yet begun and may not be detected for some time. 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 2008 and 2010 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 ozone recovery.
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VI. Web Pages of Interest