The 2015 Antarctic Ozone Hole Summary: Report #4, Monday 7 September 2015
Paul Krummel and Paul Fraser
CSIRO Oceans and Atmosphere
Aspendale, Victoria
Summary
For the 2015 ozone hole we will again be reporting images and metrics calculated from both the OMI and
OMPS data products (see the instrumentation section for a description of these). Please note that due to
operational reasons, the OMPS Level 3 global gridded daily total ozone column products provided by NASA
run 4-5 days behind the current day.
By mid-August, the onset of the 2015 ozone hole was yet to start. This is the latest onset of the ozone hole
that has been seen since the mid-to-late 1980s. The mid-to-lower Antarctic stratospheric temperatures
have been colder than usual in late July/early August, with a less-than-normal stratospheric heat flux
towards the pole from mid-July onwards. On 18 August the 2015 ozone hole had begun and by 21 August
the ozone hole area had risen to 2.9 million km2 and the ozone minima had dropped to 191 DU. The low-tomid Antarctic stratospheric temperatures remained colder than usual during the third week of August. The
fourth week of August saw moderate growth in the ozone hole area, reaching 6.3 million km 2 on 26 August,
while the ozone minima showed quite a bit of variability fluctuating between 164 and 202 DU. The low-tomid Antarctic stratospheric temperatures remained colder than usual during the fourth week of August.
The last few days of August, beginning of September saw the ozone hole area increase rapidly to be
approximately 15 million km2 by 4 September, but large variability remained in the ozone hole minima,
dropping to 161 DU on 1 September before rising again to 184 DU on 4 September. The low-to-mid
Antarctic stratospheric temperatures remained colder than usual during this period.
The 2015 ozone hole
Ozone hole area
By mid-August, the 2015 ozone hole had essentially yet to appear, with the OMI data indicating no area
where the total column ozone was less than 220 DU. The OMPS data indicate some small excursions below
220 DU in early August, but nothing since. This is the latest onset of the ozone hole since the mid-to-late
1980s.The 2015 ozone hole finally started to form on 18 August, and by 21 August the ozone hole area had
grown to 2.9 million km2. The ozone hole area continued to grow during the fourth week of August
reaching 6.3 million km2 on 26 August before dropping back to just under 5 million km2 on 27 August. The
development of this years’ hole based on this metric is similar to the 2010 ozone hole, which was also a late
developing hole but was a persistent hole as well.
The last few days of August, beginning of September saw the ozone hole area increase rapidly to be
approximately 15 million km2 by 4 September, which is close to the long-term 1979-2014 average for this
time of year, and similar to the 2012 & 2014 ozone holes.
Ozone deficit
The bottom panel of Figure 1 shows that by mid-August there was no estimated daily ozone deficit to date.
By the end of the third week of August the estimated daily ozone deficit had reached 1 million tonnes. The
fourth week of August saw the daily ozone deficit remain quite low below 2 million tonnes.
The beginning of September saw the daily ozone hole deficit reach 5 million tonnes before dropping back to
about 4 million tonnes by 4 September. This is well below the long-term 1979-2014 average for this time of
year and is similar to the 2010 ozone hole.
Ozone hole minima
By mid-August the OMI ozone minima had not yet dropped below the 220 DU threshold, but it is expected
to do so in the next week (current minima is approximately 225 DU). The OMPS minima did fall below 220
DU on 3, 5 & 6 August due to a few ‘pixels’ right at the polar vortex edge reaching just below this threshold.
On 18 August the ozone minima dropped sharply below 220 DU indicating the beginning of the 2015 ozone
hole, and by 21 August the minima had dropped to 191 DU, close to the long-term 1979-2014 average. The
OMPS minima appears to have dropped below, and remained below 220 DU, 2-3 days earlier than the OMI
data show, but the timing of the onset can be uncertain due to the large variability in this metric during the
first few weeks of August. The daily ozone minima continued to be quite variable during the fourth week of
August dropping to 164 DU on 24 August before increasing to 202 DU on 27 August. The variability in this
metric will reduce in the next one to two weeks as the polar night reduces.
The variability in the ozone hole minima continued during the last days of August through early September,
dropping to 161 DU on 1 September before rising again to 184 DU on 4 September.
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 that the ozone hole for 2015 is yet to commence by mid-August. During the
third week of August the average amount of ozone in the hole dropped rapidly to be at 203 DU on 21
August. Similar to the ozone minima, this metric is showing quite a bit of variability, dropping to 195 DU on
24 August before rising again to 213 DU on 27 August.
The average ozone amount in the hole also continued to show quite a bit of variability, dropping to 194 DU
on 1 September before rising again to 207 DU on 4 September.
Total column ozone images
Total column ozone data over Australia and Antarctica for 20 August – 4 September 2015 from OMI are
shown in Figure 3 and for 14 - 29 August 2015 from OMPS are shown in Figure 4.
By the end of the second week of August the Antarctic polar night region still covered most of Antarctica,
with essentially no sign yet of any areas below the 220 DU threshold that defines the Antarctic ozone hole.
What is quite evident, compared to recent years, is the lack of the strong ridge of high ozone in the band
immediately south of Australia between about 40-60°S. The areas of higher ozone that are present in this
latitude band appear to be patchy, possibly indicating some wave activity. The third week of August saw
the 2015 ozone hole begin to form, which can be seen as small areas indicated by the red 220 DU contour
predominantly in the region of 150°W to 60°W at around 70°S during 18-21 August. During the fourth week
of August the ozone hole continued to form in the region of 0°W to 90°W before propagating to the region
between 0°E to 120°E. On 28 August, the Australian Antarctic stations of Mawson and Casey were within
the 220 DU contour.
The formation of the 2015 ozone hole can be clearly seen in the images from 30 August through to 4
September, as the red 220 DU contour progressively grew during this period. It is expected that the 2015
ozone hole will fully form during the next week, which will see the areas below 220 DU completely join up
and the 220 DU contour will close to encircle the Antarctic continent. The Australian Antarctic stations of
Mawson, Davis and Casey were within or on the edge of the 220 DU contour on 30-31 August, and again on
4 August. The lack of the strong ridge of high ozone in the band immediately south of Australia between
about 40-60°S is still evident and quite unusual compared to most previous years.
NASA MERRA heat flux and temperature
The MERRA 45-day mean 45-75°S heat fluxes at 50 & 100 hPa are shown in Figure 5. 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 6, these usually
show an anti-correlation to the heat flux.
During June the 45-75°S heat flux at 50 & 100 hPa was in the lower 10-30% of the 1979-2014 range,
indicating a larger amount of heat transported towards the pole than average. During July, at both the 50 &
100 hPa levels, this transitioned to be in the upper 10% range at 50 hPa and 70-90% range at 100 hPa,
indicating a strong reduction in the heat transported towards the pole. By the end of the third week of
August, the 45-75°S heat flux at 50 hPa was at the maximum seen for the 1979-2014 range for this time of
year, and at 100 hPa was at the 90th percentile mark of the 1979-2014 range, both continuing to indicate
reduced heat transport towards the pole. During the fourth week of August, the 45-75°S heat flux at 50 hPa
was higher than the maximum seen for the 1979-2014 range for this time of year, and at 100 hPa was in
the highest 10th percentile mark of the 1979-2014 range, both continuing to indicate reduced heat
transport towards the pole. The last few days of August saw the 45-75°S heat flux at 50 & 100 hPa remain
in the highest 10th percentile mark of the 1979-2014 range.
Correspondingly, the 60-90°S zonal mean temperatures at 50 & 100 hPa were, overall, similar to the 19792014 average, with some deviations above and below this line in June & July. The beginning of August saw
the 60-90°S zonal mean temperatures at both 50 & 100 hPa to be at or just below the previous recorded
lowest minimums for this time of year. By mid-August the temperatures had trended up to once again be
close to the long-term averages. The third week of August saw the 60-90°S zonal mean temperatures at
both the 50 & 100 hPa levels drop to be at the lower 10% percent mark of the 1979-2014 range by 21
August, indicating quite cold conditions in the low-to-mid Antarctic stratosphere. The fourth week of
August saw the 60-90°S zonal mean temperatures at both the 50 & 100 hPa levels remain quite cold in the
lower 10-30% percent mark of the 1979-2014 range. The last days of August saw the 60-90°S zonal mean
temperatures at both the 50 & 100 hPa levels remain quite cold, with the 50 hPa trace remaining in the
lower 10-30% percent mark of the 1979-2014 range, and the 100 hPa trace just inside the lower 30-50%
mark of the 1979-2014 range.
At 50 hPa, the type 1 PSC (HNO3.3H2O) formation threshold temperature (195 K) was reached in late June.
At 100 hPa, the threshold temperature was reached during the second week of July.
Note a brief description of MERRA is given in the Definitions at the end of this report.
Summary: WMO Antarctic Ozone Bulletins – No. 1, 1 September 2015
The 2015 (and previous years) WMO Antarctic Ozone
http://www.wmo.int/pages/prog/arep/gaw/ozone/index.html
Bulletins
are
available
from
Temperatures and PSCs
Stratospheric temperatures over Antarctica have been below the PSC type I (nitric acid trihydrate: NAT)
threshold of 194.6 K since 11 May and below the PSC type II threshold of 187.8 K since 3 June. The daily
minimum temperatures at the 50 hPa level have been below the 1979-2014 average since mid April. On
several days in April, May, July and August the 50 hPa minimum temperature was below the 1979-2014
minimum. The average temperature at 50 hPa over the 60-90°S region was oscillating around the long term
mean until mid-July, after which it has been below the long term mean. In early August it was close to the
1979-2014 minimum. At 10 hPa, the 60-90°S mean temperature has been close to or above the long term
mean on most of the days during the April to August time period, with a few days below the mean.
Since the onset of NAT temperatures in early May, the NAT area was oscillating around the long term mean
in May and June and remained close to the average in July. In August the NAT area has been well above the
long term mean on most days. On 5th August the NAT area reached a maximum for the season with 28.2
million km2, which is higher than the maximum reached in recent years. One has to go back to 2009 to find
a higher PSC area maximum (28.4 million km2).
The NAT volume was relatively low between late May and early August: It was below the long-term mean
and also below the NAT volume of recent years. During August the NAT volume was similar to that of
recent years (2011, 2013 and 2014) and superior to that of 2012.
Heat Flux
During May the 45-day mean of the heat flux at 100 hPa was lower than or close to the 1979-2014 average.
In June it was somewhat larger than the long term average. In July and August the heat flux has been
noticeably smaller than the long term mean. This is an indication of a stable vortex.
At the 46.5 hPa level (altitude of ~18.5-19.5 km) the vortex is now almost entirely depleted of hydrochloric
acid (HCl), one of the reservoir gases that can be transformed to active chlorine. The area affected by HCl
removal in 2015 is similar to or larger than in recent years (2010-2014). In the sunlit collar along the vortex
edge there are regions with 2.0-2.1 ppbv of active chlorine (chlorine monoxide, ClO), and ozone depletion
has started.
Satellite Observations
Satellite observations show that the area where total ozone is less than 220 DU (“ozone hole area”) has
been significantly above zero since 18 August. This is a relatively late onset of ozone depletion. The ozone
hole area on 27 August was approx. 5.1 million km2, about half the long term average. The date of the
onset of ozone depletion varies considerably from one year to the next, depending on the position of the
polar vortex and availability of sunshine after the polar night. In 2015, the vortex has been relatively stable
and concentric around the South Pole. This can explain the late onset of ozone depletion.
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 this year’s 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 polar stratospheric clouds so far indicate that the degree of
ozone loss in 2015 will be similar to that observed in 2014 and 2013 and probably somewhat larger than in
2010 and 2012.
Satellite Instrumentation
OMI
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, have been 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.
OMPS
OMPS (Ozone Mapping and Profiler Suite) is a new ozone instrument on the Suomi National Polar-orbiting
Partnership satellite (Suomi NPP), which was launched on 28 October 2011 and placed into a sunsynchronous orbit 824 km above the Earth. The partnership is between NASA, NOAA and DoD (Department
of Defense), see http://npp.gsfc.nasa.gov/ for more details. OMPS will continue the US program for
monitoring the Earth's ozone layer using advanced hyperspectral instruments that measure sunlight in the
ultraviolet and visible, backscattered from the Earth's atmosphere, and will contribute to observing the
recovery of the ozone layer in coming years. For the 2014 ozone hole season, we will also be using the
OMPS total column ozone data by producing metrics from both OMI and OMPS Level 3 global gridded daily
total ozone column products from NASA, and present both sets of results for comparison. NOTE that NASA
receive the raw OMPS data from NOAA, and due to some operational delays, NASA have decided to delay
the processing of data by 96 hours (4 days) from the time they obtain the first raw data for a given day. As a
result, the OMPS Level 3 global gridded daily total ozone column products provided by NASA run 4-5 days
behind the current day.
Figure 1: Ozone hole area (top panel) and estimated daily ozone deficit (bottom panel) based on OMI (data
up to 4 September 2015) and OMPS (data up to 29 August 2015) satellite data.
Figure 2: Ozone hole depth (top panel) and average ozone amount within the ozone hole (bottom panel)
based on OMI (data up to 4 September 2015) and OMPS (data up to 29 August 2015) satellite data.
Figure 3: OMI ozone hole images for 20 August – 4 September 2015; 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: OMPS ozone hole images for 14 – 29 August 2015; 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 OMPS instrument requires solar radiation to the earth’s surface
in order to measure the column ozone abundance. Note that due to operational reasons, the OMPS Level 3
global gridded daily total ozone column products provided by NASA run 4-5 days behind the current day.
Figure 5: 45-day mean 45°S-75°S eddy heat flux at 50 & 100 hPa. Images courtesy of NASA GSFC,
downloaded 7 September 2015, data through to 1 September 2015:
http://ozonewatch.gsfc.nasa.gov/meteorology/flux_2015_MERRA_SH.html
Figure 6: 60°S-90°S zonal mean temperature at 50 & 100 hPa. Images courtesy of NASA GSFC, downloaded
7 September 2015, data through to 1 September 2015:
http://ozonewatch.gsfc.nasa.gov/meteorology/temp_2015_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, NASA 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 (< -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 & OMPS: the Total Ozone Mapping Spectrometer (TOMS), Ozone Monitoring Instrument (OMI),
and Ozone Mapping and Profiler Suite (OMPS) 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. The OMPS Level 3 data used in this report were created from a
research dataset developed by NASA's NPP Ozone Science Team using nadir measurements from SuomiNPP's Ozone Mapping and Profiler Suite(OMPS). All data were downloaded from
ftp://jwocky.gsfc.nasa.gov/pub.