The 2012 Antarctic Ozone Hole Summary: Report #3, Monday 3 September 2012
Paul Krummel and Paul Fraser
Centre for Australian Weather and Climate Research
CSIRO Marine & Atmospheric Research
Aspendale, Victoria
Instrumentation
Data from the Ozone Monitoring Instrument (OMI) on board the Earth Observing Satellite
(EOS) Aura, that have been processed with the NASA TOMS Version 8.5 algorithm, will be
utilized again this year in our weekly ozone hole reports. OMI continues the NASA TOMS
satellite record for total ozone and other atmospheric parameters related to ozone chemistry
and climate.
On 19 April 2012 a reprocessed version of the complete (to date) OMI Level 3 gridded data
was released. This is a result of a post-processing of the L1B data due to changed OMI row
anomaly behaviour (see below) and consequently followed by a re-processing of all the L2 and
higher data. These new data have now been reprocessed by CSIRO, which has resulted in
small changes in the ozone hole metrics we calculate, and as such, these metrics may be
slightly different for previous years for OMI data (2005-2011).
In 2008, stripes of bad data began to appear in the OMI products apparently caused by a small
physical obstruction in the OMI instrument field of view and is referred to as a row anomaly.
NASA scientists guess that some of the reflective Mylar that wraps the instrument to provide
thermal protection has torn and is intruding into the field of view. On 24 January 2009 the
obstruction suddenly increased and now partially blocks an increased fraction of the field of
view for certain Aura orbits and exhibits a more dynamic behaviour than before, which led to
the larger stripes of bad data in the OMI images. Since 5 July 2011, the row anomaly that
manifested itself on 24 January 2009 now affects all Aura orbits, which can be seen as thick
white stripes of bad data in the OMI total column ozone images. It is now thought that the row
anomaly problem may have started and developed gradually since as early as mid-2006.
Despite various attempts, it turned out that due to the complex nature of the row anomaly it is
not possible to correct the L1B data with sufficient accuracy (≤ 1%) for the errors caused by the
row anomaly, which has ultimately resulted in the affected data being flagged and removed
from higher level data products (such as the daily averaged global gridded level 3 data used
here for the images and metrics calculations). However, once the polar night reduces enough
then this should not be an issue for determining ozone hole metrics, as there is more overlap of
the satellite passes at the polar regions which essentially ‘fills-in’ these missing data.
The 2012 ozone hole
By mid-August, the ozone hole area was still quite small at around 2 million km2 (Figure 1, top
panel), which is similar to the 2010 ozone hole in size and onset date. The onset of this years’
hole appears to be about a week later than the recent large ozone holes (2006-2009, 2011).
During the third week of August, the ozone hole area rose sharply to peak at almost 6 million
km2 before dropping back around 3 million km2, which is very similar to the 2010 ozone hole.
The similarities to the 2010 ozone hole have continued during the fourth week of August with
the ozone hole area rising to 10 million km2, almost identical to the 2010 ozone hole but
considerably smaller than the other recent large ozone holes (2006-2009, 2011).
The bottom panel of Figure 1 shows that the estimated daily ozone deficit by mid-August was
less than 1 million tonnes. This rose to about 2 million tonnes during the third week of August
before dropping below 1 million tonnes, again, very similar to the 2010 ozone hole. By the end
of August the ozone deficit had risen again to about 3 million tonnes, almost identical to the
2010 hole and much less than the recent large ozone hole.
During the second week of August, the ozone minimum dropped below 220 DU, similar to the
2010 ozone hole and about a week later than in 2006-2009 & 2011. By the mid-August, the
ozone minimum in the Antarctic ozone hole had dropped rapidly to 185 DU (similar to most of
the recent ozone holes; Figure 2, top panel). This continued to drop to 180 DU during the third
week of August before rising to around 205 DU, almost identical in behaviour to the 2010 ozone
hole. At the end of August the ozone hole minima was again around 180 DU, having briefly
dropped to 160 DU on 25th August, and like the other metrics, is similar to the 2010 ozone hole.
The average ozone amount in the hole (averaged column ozone amount in the hole weighted
by area; Figure 2 bottom panel) shows a minima of about 206 DU by mid-August, but it is
clearly still highly variable. This is illustrated during the third week of August when this metric
dropped to 204 DU before rising again to around 213 DU, and dropping again to 205 DU by the
end of August. The really rapid ozone decline in this metric in most of the previous years’ did
not start until the end of August or the first week of September – presumably this will be the
case for 2012.
It should be noted that the above metrics are subject to variability, noise and inaccuracies
during the period when the polar night is larger than the ozone hole.
Total column ozone images
Total column ozone data over Australia and Antarctica for 20 – 31 August are shown in Figure
3. The Antarctic polar night region still covers most of Antarctica, with the 220 DU contour
barely visible on the images from 11-17 August. An ozone maximum was present in a ridge
immediately south of Australia during the period 1-8 August, with a maximum in excess of 450
DU reached on 7 August. Another intense ridge formed on 13 August around 60°S latitude
immediately south of the African continent and has proceeded to move eastwards to be south
west of Australia on 17 August. The maximum in this ridge appears to be around 500 DU. This
ridge continued to strengthen and grow in size, and during the period 19-21 August lay above
the edge of the Antarctic continent above the Australian Antarctic stations. By 24 August the
ridge had moved eastward and dissipated. The polar vortex during this period (19-24 August)
can been seen to be quite distorted, with the axis of distortion rotating from ~ 0-180° on 19
August to ~60°E-90°W on 24 August. This helps illustrate/explain the slower start to this years’
ozone hole. During the last week of August the polar vortex appeared to become more
symmetrical again, with a small ridge of ozone present on 29 & 30 Aug around 55°S and 80110°E (north of the Australian Antarctic Stations).
NASA MERRA heat flux and temperature
The MERRA 45-day mean 45-75°S heat fluxes at 100 & 50 hPa are shown in Figure 4. A less
negative heat flux usually results in a colder polar vortex, while a more negative heat flux
indicates heat transported towards the pole (via some meteorological disturbance/wave) and
results in a warming of the polar vortex. The corresponding 60-90°S zonal mean temperatures
at 100 & 50 hPa are shown in Figure 5, these usually show an anti-correlation to the heat flux.
Note a brief description of MERRA is given in the Definitions at the end of this report.
During the second half of August a significant negative heat flux event occurred and can be
seen in both the 100 & 50 hPa traces. At the 50 hPa level the 2012 heat flux is in the bottom
10-30% of the 1979-2011 range. Correspondingly, a peak in the 60-90°S zonal mean
temperatures at 100 & 50 hPa can be seen for this period. The peak lies in the top 10% of the
1979-2011 range, and on 20 Aug at the 50 hPa level, was briefly above any previous maximum
for that day. This disturbance explains the slower start to this years’ ozone hole and correlates
with the above mentioned distortion of the polar vortex during 19-24 August.
Summary: WMO Antarctic Ozone Bulletins #1, 22 August 2012
The WMO Bulletins use ozone data from the NASA satellite-borne OMI instrument as well as
data from the GOME-2 instrument on the MetOp satellite. GOME-2 is the follow-up instrument
for SCIAMACHY and data from both instruments (GOME-2, SCIAMACHY) are assimilated in
the WMO Bulletins.
Stratospheric Temperatures
Stratospheric temperatures over Antarctica have been below -78°C (the temperature threshold
for the formation of Type I PSCs: NAT - HNO3.3H2O) since mid-May and below -85°C (the
temperature threshold for the formation of Type II PSCs: ice H2O) since early June. The
average temperature over the 60-90°S region has been close to or below the long-term mean
until mid-August. The August mean temperature has been higher than in 2009 and 2011 but
lower than in 2010.
Ozone Hole Area
The area where total column ozone has been less than 220 DU has been above zero for only a
few days (ozone depletion only occurs after the region contained the active chlorine becomes
sunlit). The generation of active chlorine requires the presence of PSCs. An estimate of the
possible ozone hole area (usually achieved by mid-September) at this early stage of the
season comes from the area of the Antarctic stratosphere within which PSCs (NAT) have
formed (this is directly linked to the amount of ozone loss that will occur later in the season) –
this peaked at 25 million km2 in early June and has stayed relatively constant since June at
about 23-24 million km2, significantly below the 1979-2011 average.
This suggests that the ozone loss in 2012 will be relatively moderate compared to recent years,
probably less than in 2009 and 2011 but perhaps larger than in 2010.
Vortex Stability
The longitudinally-averaged heat flux between 45°S and 75°S in the stratosphere is an
indication of how much the Antarctic stratosphere is disturbed. During May and June the heat
flux was close to the 1979-2011 average, but has been larger than the average in July and
August, again indicative of an ozone hole weaker (more disturbed) than in recent years.
New Ozone Satellite (NASA: The Earth Observer April 2012)
OMPS (Ozone Mapping and Profiler Suite) is a new ozone instrument on the Suomi National
Polar-orbiting Partnership satellite (Suomi NPP). The partnership is between NASA, NOAA and
DoD (Department of Defense), see http://npp.gsfc.nasa.gov/ for more details.
OMPS data will contribute to observing the recovery of the ozone layer in coming years.
Currently we are using KNMI/NASA’s OMI data from the AURA satellite to assess the 2012
Antarctic Ozone Hole. Presumably OMPS data will be used in the near future.
Figure 1: Ozone hole area (top panel) and estimated daily ozone deficit (bottom panel) based
on OMI satellite data, as of 31 August 2012.
Figure 2: Ozone hole depth (top panel) and average ozone amount within the ozone hole
(bottom panel) based on OMI satellite data, as of 31 August 2012.
Figure 3: OMI ozone hole images for 20 – 31 August 2012; the ozone hole boundary is
indicated by the red 220 DU contour line. The Australian Antarctic (Mawson, Davis and Casey)
and Macquarie Island stations are shown as red plus symbols. The white area over Antarctica
is missing data and indicates the approximate extent of the polar night. The OMI instrument
requires solar radiation to the earth’s surface in order to measure the column ozone
abundance. The white stripes are bad/missing data due to a physical obstruction in the OMI
instrument field of view.
Figure 4: 45-day mean 45°S-75°S eddy heat flux at 100 & 50 hPa. Image courtesy of NASA
GSFC, downloaded 3 Sep 2012:
http://ozonewatch.gsfc.nasa.gov/meteorology/flux_2012_MERRA_SH.html
Figure 5: 60°S-90°S zonal mean temperature at 100 & 50 hPa. Image courtesy of NASA
GSFC, downloaded 3 Sep 2012:
http://ozonewatch.gsfc.nasa.gov/meteorology/temp_2012_MERRA_SH.html
Definitions
CFCs: chlorofluorocarbons, synthetic chemicals containing chlorine, once used as refrigerants,
aerosol propellants and foam-blowing agents, that break down in the stratosphere (15-30 km
above the earth’s surface), releasing reactive chlorine radicals that catalytically destroy
stratospheric ozone.
DU: Dobson Unit, a measure of the total ozone amount in a column of the atmosphere, from
the earth’s surface to the upper atmosphere, 90% of which resides in the stratosphere at 15 to
30 km.
Halons: synthetic chemicals containing bromine, once used as fire-fighting agents, that break
down in the stratosphere releasing reactive bromine radicals that catalytically destroy
stratospheric ozone. Bromine radicals are about 50 times more effective than chlorine radicals
in catalytic ozone destruction.
MERRA: is a NASA reanalysis for the satellite era using a major new version of the Goddard
Earth Observing System Data Assimilation System Version 5 (GEOS-5). The project focuses
on historical analyses of the hydrological cycle in a broad range of weather and climate time
scales. It places modern observing systems (such as EOS suite of observations in a climate
context. Since these data are from a reanalysis, they are not up-to-date. So, we supplement
with the GEOS-5 FP data that are also produced by the GEOS-5 model in near real time.
These products are produced by the NASA Global Modeling and Assimilation Office (GMAO).
Ozone: a reactive form of oxygen with the chemical formula O3; ozone absorbs most of the UV
radiation from the sun before it can reach the earth’s surface.
Ozone Hole: ozone holes are examples of severe ozone loss brought about by the presence of
ozone depleting chlorine and bromine radicals, whose levels are enhanced by the presence of
PSCs (polar stratospheric clouds), usually within the Antarctic polar vortex. The chlorine and
bromine radicals result from the breakdown of CFCs and halons in the stratosphere. Smaller
ozone holes have been observed within the weaker Arctic polar vortex.
Polar night terminator: the delimiter between the polar night (continual darkness during winter
over the Antarctic) and the encroaching sunlight. By the first week of October the polar night
has ended at the South Pole.
Polar vortex: a region of the polar stratosphere isolated from the rest of the stratosphere by
high west-east wind jets centred at about 60°S that develop during the polar night. The isolation
from the rest of the atmosphere and the absence of solar radiation results in very low
temperatures (less than -78°C) inside the vortex.
PSCs: polar stratospheric clouds are formed when the temperatures in the stratosphere drop
below -78°C, usually inside the polar vortex. This causes the low levels of water vapour present
to freeze, forming ice crystals and usually incorporates nitrate or sulphate anions.
TOMS & OMI: the Total Ozone Mapping Spectrometer & Ozone Monitoring Instrument, are
satellite borne instruments that measure the amount of back-scattered solar UV radiation
absorbed by ozone in the atmosphere; the amount of UV absorbed is proportional to the
amount of ozone present in the atmosphere.
UV radiation: a component of the solar radiation spectrum with wavelengths shorter than those
of visible light; most solar UV radiation is absorbed by ozone in the stratosphere; some UV
radiation reaches the earth’s surface, in particular UV-B which has been implicated in serious
health effects for humans and animals; the wavelength range of UV-B is 280-315 nanometres.
Acknowledgements
The TOMS and OMI data are provided by the TOMS ozone processing team, NASA Goddard
Space Flight Center, Atmospheric Chemistry & Dynamics Branch, Code 613.3. The OMI
instrument was developed and built by the Netherlands's Agency for Aerospace Programs
(NIVR) in collaboration with the Finnish Meteorological Institute (FMI) and NASA. The OMI
science team is lead by the Royal Netherlands Meteorological Institute (KNMI) and NASA.