The 2013 Antarctic Ozone Hole Summary: Report #5, Tuesday 24 September 2013
Paul Krummel and Paul Fraser
Centre for Australian Weather and Climate Research
CSIRO Marine & Atmospheric Research
Aspendale, Victoria
Summary
Contrary to earlier indications, thus far into the season, the 2013 Antarctic ozone hole looks like
it may be similar to the intermediate ozone holes of 2010 and 2012. The year-to-year variability
of the ozone hole does not reflect variations in the level of ODSs in the Antarctic stratosphere,
which, based on surface observations, will have fallen since 2012. The decadal variations in the
ozone hole do reflect the long-term changes of ODSs in the Antarctic stratosphere. The ozone
hole depth in 2013 set a new record low of about 127 DU for late August since records began
in 1979, but that event appears to be not typical if this ozone hole.
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 2013 ozone hole
Ozone hole area
By mid-August, the ozone hole area was variable in size and still quite small at around 2 million
km2 (Figure 1, top panel), which is similar to the 2010 & 2012 ozone holes 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 about 7.5 million km2 on 21 August. By 30 August, the ozone hole had more
than doubled in area to almost 17 million km2 compared to a week ago.
During the first week of September, the ozone hole area rose to close to 20 million km 2, before
falling to 16-17 million km2 by 6 September. By 16 September the ozone hole area had risen
sharply to 24 million km2 (which may have been the peak area) and by 21 September the area
had fallen to 23 million km2. At present the ozone hole area is between what it was in 2009 and
2010.
Ozone deficit
The bottom panel of Figure 1 shows that the estimated daily ozone deficit by the end of the
third week of August was around 2 million tonnes. This is similar to the 2008, 2010 and 2012
ozone holes for that same time of year. During the 3rd week of August the ozone hole deficit
rose to 7 Mt, then declined and then again rose to 7 Mt by the end of August.
At the end of the first week of September the ozone deficit reached 11-12 Mt, similar to 2008
and just below the deficit in 2011. By 13 September the deficit rose sharply to 22-23 Mt, similar
to 2008, 2009 and 2011 and much larger (by more than a factor of 2) than 2010 and 2012.
However it appears that by 21 September the deficit has stopped growing and it now looks
similar to 2010 and 2012. This hole may now be significantly smaller than we first suggested,
although the peak deficit usually occurs during the last week of September – first week of
October.
Ozone hole minima
During the first and second weeks of August, the ozone minimum fluctuated sharply and
dropped below 220 DU on several occasions, similar to previous ozone holes. By the end of the
third week of August, the ozone minimum in the Antarctic ozone hole had dropped to 179 DU,
similar to the recent large ozone holes (Figure 2, top panel). This rapid drop in ozone minimum
continued and early in the 4th week of August reached a record-equalling (since 1979) low of
125-130 DU. By the end of August the minimum has recovered to just under 160 DU.
During the first week of September consistently low minima were observed at about 140 DU,
similar to 2008 and 2009. By 13 September the ozone minimum fell to close to 135 DU,
identical to 2009 and lower than all other recent ozone holes (2008, 2010-2012). By 21
September the ozone minimum had increased to 140 DU, now similar to 2010 and 2012. The
minimum ozone in this hole may not go any lower, although the minimum usually occurs in the
first week of October.
Average ozone in the 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
rose to 216 DU before dropping again to around 207 DU. 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 2013. By the end of August the anticipated
rapid decline in average ozone in the hole had not commenced, remaining at about 200 DU,
although it did fall to nearly 190 DU about a week ago, before recovering again.
The expected rapid decline during the first week of September did eventuate as predicted and
reached 185-190 DU by 6 September, tracking the 2011 behaviour, and reaching 175 DU by 13
September, similar to 2011 and 2008, but slightly above 2009. The average ozone stayed
between 175 and 180 DU for the period of 13-21 September, and is now similar to 2010 and
2012.
Total column ozone images
Total column ozone data over Australia and Antarctica for 10 September – 21 September 2013
are shown in Figure 3.
The Antarctic polar night region still covers most of Antarctica, with the 220 DU contour
becoming quite visible on the images from 19-23 August. An ozone maximum was present in a
ridge immediately south of Australia during much of the period 12-23 August, but the ridge is
not as strong as seen last year during the same period. On several occasions (13, 14, 19 & 20
August) a small pocket of low ozone (< 220 DU) formed in the region south of South America.
By the end of August the 220 DU contour at >60oS latitude is nearly completely present at all
longitudes. The region of lowest ozone (< 175 DU) remains near the edge of the ozone hole,
just SW of the southern tip of S. America. To date the Australian Antarctic bases have
remained outside the ozone hole, except perhaps Mawson and Davis on 29 August.
During 1-3 September the ozone hole passed over the southern tip of S. America. By 2
September virtually all of the Antarctic continent was under the ozone hole (as defined by the
220 DU contour), with the possible exception of all of the Australian Antarctic bases. By 8-9
September, the ozone hole (the Antarctic vortex) became quite distorted, although by 13
September, progress towards a more symmetrical vortex was seen. Unusually, the section of
Antarctica that contains the Australian bases has persistently remained outside the ozone hole
for virtually all of September, except for Mawson and Davis (our most westerly stations), which
were right on the 220 DU contour on 12-14 September. This ozone hole persists in its
asymmetry – by 21 September none of the Australian Antarctic bases spent any significant time
under the hole (within the 220 DU contour).
Since 24 August, a large ridge of ozone has persisted South of the Australian continent, with a
high ozone event over Macquarie Island on 27 August. This ridge of ozone dissipated during
the first week of September and ozone levels of under 300 DU were observed over Macquarie
Island on 4 September. The ozone ridge reformed south of E. Africa commencing 3 September,
touching the Antarctic continent (over the Australian bases) on 6 September, with ozone levels
approaching 400 DU. The ridge of high ozone stayed over the Australian bases until 10
September, when a slight easterly rotation of the vortex brought Mawson and Davis close to or
on the 220 DU contour. The massive ridge of high ozone has persisted over the Australian
Antarctic bases and perhaps as much as 1/3 of the Antarctic continent remains outside the
hole. Since 17 September through to 21 September even the South Pole is just within the 200
DU contour and the polar vortex is very elongated along the longitude axis of 30°E – 150°W.
An easterly vortex rotation over the next week or so will see the southern tip of S. America well
inside the 220 DU contour.
NASA MERRA heat flux and temperature
The MERRA 45-day mean 45-75°S heat fluxes at 50 & 100 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 50 & 100 hPa are shown in Figure 5, these usually show an anti-correlation to the heat flux.
During the first three weeks of August the heat flux at 50 hPa was in the upper 50-70% of the
1979-2012 range and the 100 hPa trace was in the 70-90% of the 1979-2011 range. By the end
of August both the 50 hPa and 100 hPa heat fluxes were tracking the 1979-2012 long-term
averages, significantly lower than the 2012 heat fluxes, indicative of a more stable and colder
vortex in 2013 compared to 2012.
The heat fluxes increased during the first week of September and are now larger than they
were in 2012. Then increased heat fluxes continued into the 2nd week but by 13 September the
heat fluxes decreased again and continued to decrease to 19 September. They continue to be
very close to 2012 values, larger than the long-term average (1979-2012). With heat fluxes as
large as they were in 2012, it is difficult to see how the 2013 hole will be so-called ‘large’ – we
suspect ‘intermediate’ will be the outcome and, if so, will continue the trend towards ozone hole
recovery.
Correspondingly, the 60-90°S zonal mean temperatures at 100 & 50 hPa were in the lowest 030% range, with the 100 hPa zonal mean temperature during the second week of August being
below the previous minimum seen between 1979 and 2012. This indicates that the mid-to-lower
Antarctic stratosphere is relatively cold this year. By the end of August vortex warming had
commenced at 50 hPa (since early August) and at 100 hPa since about the 3rd week of August,
both following the long-term averages.
By the end of the first week of September vortex warming had continued at 50 hPa and
commenced at 100 hPa. By 13 September and now 19 September, the expected warming
continued, being very close to the 2012 trajectory and now above the 1979-2012 long-term
mean.
At 50 hPa, the type 1 PSC (HNO3.3H2O) formation threshold temperature (195K) was reached
in late June and stayed below this threshold until the first week of September. By 13 September
the threshold temperature was exceeded, as expected from the long-term mean trends.
At 100 hPa, the threshold temperature was reached at the beginning of July and the 100 hPa
temperature remains below this threshold. By 13 September the zonal mean temperature was
right on the threshold temperature, but well above by 19 September.
The zonal mean temperatures at both levels are now slightly above the 1979-2012 mean,
despite reaching near-record lows in July and August.
Note a brief description of MERRA is given in the Definitions at the end of this report.
Summary: WMO Antarctic Ozone Bulletins - No. 1, 23 August; No. 2, 8 September
The 2013 (and previous years) WMO Antarctic Ozone Bulletins are available from
http://www.wmo.int/pages/prog/arep/gaw/ozone/index.html.
Antarctic stratospheric temperatures
The daily minimum temperatures at the 50 hPa level (about 20 km) south of 50°S have been
below the 1979-2012 average since early April. From mid-June until mid-August, the minimum
temperature has been well below the long-term mean. From-mid August the minimum
temperature has increased, but is still below the long-term mean. The minimum temperature
has been below the polar stratospheric cloud (PSC) formation threshold since early-May (see
below).
The average temperature over the 60-90°S region has been below the long-term (1979-2012)
mean from April until mid-August, with only a few exceptions. On 11 August it dipped below the
1979-2012 minimum (the coldest 2nd week of August over the entire 1979-2013 period). From
mid-August, the mean temperature has increased and is now near the long-term mean.
Polar Stratospheric Clouds (PSCs)
The major component of PSCs is nitric acid trihydrate (NAT): HNO 3(H2O)3. The formation of
NAT crystals in the Antarctic stratosphere at around -80°C provides an active surface for the
formation of ozone-destroying chlorine (Cl2) from otherwise ozone-benign chlorine reservoir
species – hydrochloric acid (HCl) and chlorine nitrate (ClONO2). HCl and ClONO2 are formed
when CFCs (chlorofluorocarbons) and other chlorine-containing species break down in the
stratosphere.
The amount of NAT formed in the Antarctic stratosphere early in each ozone-hole season
determines, to a significant degree, the level of ozone loss that will occur later in the season.
NAT amounts are measured at NAT area and volume. Since the onset of NAT temperatures
(less than -80°C) in early May, the NAT area was above the 1979-2012 average until late June.
After that it has been near the long term mean. The NAT area reached a peak of 26.3 million
km2 on 19 July. Since early June the NAT area has been smaller in 2013 than in 2011 but
larger than in 2010 and 2012 on most days. As of % September the NAT area is 3 million km2
larger than the long-term mean.
Since the appearance of PSCs in early May, until mid-July, the NAT volume was close to or
above the 1979-2012 average. From mid-July the NAT volume has been somewhat lower than
the long-term mean. The NAT volume has been larger in 2013 than in 2010 and 2012 and
similar to the volume seen in 2011. In mid-August the NAT volume increased and has been
close to the long-term since then.
Vortex Stability
The longitudinally-averaged heat flux between 45°S and 75°S is an indication of how much the
Antarctic stratosphere is disturbed. During May, June and most of July the 45-day mean of the
heat flux was lower than or close to the 1979-2012 average. In August the heat flux has
oscillated around the long term mean. As of 5 September the heat flux is larger than in the
three most recent years.
Chemical Activation of the Antarctic Stratosphere
The Antarctic polar vortex is now chemically activated and primed for ozone depletion. It now
requires the sun to illuminate the vortex to instigate significant ozone depletion.
At 19-20 km the vortex is now almost entirely depleted of HCl. The area affected by HCl
removal is slightly larger in 2013 compared to recent years (2010-2012). In the sunlit collar
along the vortex edge there are regions with 1.5-1.8 ppb (parts per 109 molar) of active chlorine
(chlorine monoxide: ClO), and ozone depletion has just started. In 2013 the vortex seems
somewhat more chemically-activated than in 201 and 2011 and similar to 2012.
Ozone Hole Area
In previous years, the ozone hole area data were obtained from the SCIAMACHY instrument
on Envisat satellite (launched 2002, ceased operation 2012, sun-synchronous polar orbit). In
2013 the satellite observations are from the GOME-2 instrument on the Metop satellites (three
polar orbiting meteorological satellites launched 2006, operated by the European Organisation
for the Exploitation of Meteorological Satellites: EUMETSAT). The GOME-2 data show that the
area with total ozone less than 220 DU, the so-called ‘ozone hole area’, has been significantly
above zero since 5 August. The ozone hole area is now (20 August) similar to 2011 and larger
than in 2010 and 2012. However, the onset of ozone depletion varies considerably from one
year to the next, depending on the position of the polar vortex and availability of daylight after
the polar night. It is too early to say with certainty just how this ozone hole will evolve over the
next weeks.
Data from the TOMS/OMI instrument on the EOS Aura satellite (launched 2004) show that the
2013 ozone hole area became persistently non-zero at the beginning of August, reached a
temporary peak of 7x106 km2 by 8 August and has re-grown to reach 9x106 km2 by 20 August.
By 6 September the ozone hole area had passed 15 million km2. This looks similar to the ozone
hole behavior in 2011 and 2012.
Ground-Based Ozone Measurements at Australian Antarctic sites
Measurements with ground based instruments and with balloon sondes show first signs of
ozone depletion at several sites. Weekly ozone sondes from Davis (69°S, 77°E) show that
ozone depletion has commenced above Davis, with a significant ‘bite’ in the typical winter
ozone profile commencing 6 August and intensifying through sondes on August 13 and 20. The
sonde on 3 September shows that ozone depletion above Davis has progressed further. The
column ozone above Davis shows the 2013 column similar to the 2003-2012 mean column.
The Dobson total ozone column instrument on Macquarie Island (54°S,159°E) has been
operational since 1957, one of the longest continuous total-column ozone records. So far in
2013 the Macquarie Island total ozone data are tracking the 1987-2012 mean values.
Macquarie Island was close to the polar vortex edge on 10 August and recorded a low (283
DU) total ozone column. Another low column ozone value was recorded on 4 September (310
DU).
Summary
As the sun returns to Antarctica after the polar night, ozone destruction will speed up. It is still
too early to give a definitive statement about the development of the 2013 Antarctic ozone hole
and the degree of ozone loss that will occur. This will, to a large extent, depend on the
meteorological conditions. However, the temperature conditions and the extent of PSCs so far
indicate that the degree of ozone loss in 2013 will be similar to that observed in 2011 and larger
than in 2010 and 2012.
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 2013
Antarctic Ozone Hole. At some stage we will transition to using the OMPS total column ozone
data.
Figure 1: Ozone hole area (top panel) and estimated daily ozone deficit (bottom panel) based
on OMI satellite data, as of 21 September 2013.
Figure 2: Ozone hole depth (top panel) and average ozone amount within the ozone hole
(bottom panel) based on OMI satellite data, as of 21 September 2013.
Figure 3: OMI ozone hole images for 10 Sep – 21 Sep 2013; 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 green 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 50 & 100 hPa. Images courtesy of NASA
GSFC, downloaded 24 September 2013, data through to 19 September 2013:
http://ozonewatch.gsfc.nasa.gov/meteorology/flux_2013_MERRA_SH.html
Figure 5: 60°S-90°S zonal mean temperature at 50 & 100 hPa. Images courtesy of NASA
GSFC, downloaded 24 September 2013, data through to 19 September 2013:
http://ozonewatch.gsfc.nasa.gov/meteorology/temp_2013_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.