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The 2015 Antarctic Ozone Hole Summary: Final ReportFinal Report

Paul Krummel, Paul Fraser and Nada DerekCSIRO Oceans and Atmosphere

June 2016

Department of the Environment

OCEANS AND ATMOSPHERE

Oceans and Atmosphere

CitationKrummel, P. B., P. J. Fraser and N. Derek, The 2015 Antarctic Ozone Hole Summary: Final Report, Report prepared for the Australian Government Department of the Environment, CSIRO, Australia, iv, 27 pp., 2016.

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ContentsAcknowledgments............................................................................................................................................v

1 Satellite data used in this report.........................................................................................................1

1.1 TOMS.....................................................................................................................................1

1.2 OMI.......................................................................................................................................1

1.3 OMPS....................................................................................................................................1

2 The 2015 Antarctic ozone hole............................................................................................................3

2.1 Ozone hole metrics...............................................................................................................3

2.2 Total column ozone images...................................................................................................6

2.3 Antarctic meteorology/dynamics..........................................................................................7

3 Comparison to historical metrics.........................................................................................................9

4 Antarctic ozone recovery...................................................................................................................15

Appendix A 2015 daily total column ozone images................................................................................19

Definitions ............................................................................................................................................20

References ............................................................................................................................................22

The 2015 Antarctic Ozone Hole Summary: Final Report | i

FiguresFigure 1. Ozone hole ‘depth’ (minimum ozone, DU) based on OMI & OMPS satellite data. The 2015 hole based on OMI data is indicated by the thick black line while the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean....................................................................................................................3

Figure 2. Average amount (DU) of ozone within the Antarctic ozone hole throughout the season based on OMI & OMPS satellite data. The 2015 hole based on OMI data is indicated by the thick black line; the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean.......................................................4

Figure 3. Ozone hole area based on OMI & OMPS satellite data. The 2015 hole based on OMI data is indicated by the thick black line while the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean................................................................................................................................................5

Figure 4. OMI & OMPS estimated daily ozone deficit (in millions of tonnes, Mt) within the ozone hole. The 2015 hole based on OMI data is indicated by the thick black line while the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean. The estimated total (integrated) ozone loss for each year is shown in the legend..............................................................................................................................6

Figure 5. NASA MERRA heat flux and temperature. The 45-day mean 45°S-75°S eddy heat flux at 50 and 100 hPa are shown in the two left hand panels. The 60°S-90°S zonal mean temperature at 50 & 100 hPa are shown in the right two panels. Images courtesy of NASA GSFC – http://ozonewatch.gsfc.nasa.gov/meteorology/SH.html.................................................................................8

Figure 6. Minimum ozone levels observed in the Antarctic ozone hole using a 15-day moving average of the minimum daily column ozone levels during the entire ozone season for all available years of TOMS (green) and OMI (purple) data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text. The error bars represent the range of the daily ozone minima in the 15-day average window..................................................................................................................................12

Figure 7. The average ozone amount in the ozone hole (averaged column ozone amount in the hole weighted by area) for all available years of TOMS (green) and OMI (purple) data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text..................................13

Figure 8. Maximum ozone hole area (area within the 220 DU contour) using a 15-day moving average during the ozone hole season, based on TOMS data (green) and OMI data (purple). The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text. The error bars represent the range of the ozone hole size in the 15-day average window...................................................13

Figure 9. Estimated total ozone deficit for each year in millions of tonnes (Mt), based on TOMS (green) and OMI (purple) satellite data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text....................................................................................................................14

ii | The 2015 Antarctic Ozone Hole Summary: Final Report

Figure 10. Total column ozone amounts (October mean) as measured at Halley Station, Antarctica, by the British Antarctic Survey from 1956 to 2015. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text............................................................................................14

Figure 11. Equivalent Effective Stratospheric Chlorine for mid-and Antarctic latitudes (EESC-ML, EESC-A) derived from global measurements of all the major ODSs at Cape Grim (CSIRO) and other AGAGE stations and in Antarctic firn air (CSIRO) from Law Dome. EESC-A is lagged 5.5 years and EESC-ML 3 years to approximate the transport times for ODSs from the Earth’s surface (largely in the Northern Hemisphere) to the stratosphere at Southern Hemisphere mid- and Antarctic latitudes. Arrows indicate dates when the mid-latitude and Antarctic stratospheres return to pre-1980s levels of EESC, and approximately pre-ozone hole levels of stratospheric ozone.........................................................................16

Figure 12. ODGI-A and ODGI-ML indices (Hofmann and Montzka, 2009) derived from AGAGE ODS data using ODS fractional release factors from Newman et al. (2007)...................................................................17

Apx Figure A.1 OMI ozone hole images for 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............................Error! Bookmark not defined.

Apx Figure A.2 OMI ozone hole images for October 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 stripes are bad/missing data due to a physical obstruction in the OMI instrument field of view................................................Error! Bookmark not defined.

Apx Figure A.3 OMI ozone hole images for November 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 stripes are bad/missing data due to a physical obstruction in the OMI instrument field of view................................................Error! Bookmark not defined.

Apx Figure A.4 OMI ozone hole images for December 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 stripes are bad/missing data due to a physical obstruction in the OMI instrument field of view................................................Error! Bookmark not defined.

Apx Figure A.5 OMPS ozone hole images for 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...............................Error! Bookmark not defined.

Apx Figure A.6 OMPS ozone hole images for October 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..........................................................Error! Bookmark not defined.

Apx Figure A.7 OMPS ozone hole images for November 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..........................................................Error! Bookmark not defined.

Apx Figure A.8 OMPS ozone hole images for December 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..........................................................Error! Bookmark not defined.

The 2015 Antarctic Ozone Hole Summary: Final Report | iii

TablesTable 1. Antarctic ozone hole metrics based on TOMS/OMI satellite data - ranked by size or minima (Note: 2005 metrics are average of TOMS and OMI data)..............................................................................10

Table 2. ODS contributions to the decline in EESC at Antarctic and mid-latitudes (EESC-A, EESC-ML) observed in the atmosphere in 2015 since their peak values in 2000 and 1998 respectively........................15

iv | The 2015 Antarctic Ozone Hole Summary: Final Report

AcknowledgmentsThe TOMS and OMI data used in this report 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 MERRA heat flux and temperature images are courtesy of NASA GSFC (http://ozonewatch.gsfc.nasa.gov/meteorology/SH.html).

The OMPS total column ozone data used in this report are provided by NASA's NPP Ozone Science Team at the Goddard Space Flight Center, Atmospheric Chemistry & Dynamics Branch, Code 613.3 (see http://ozoneaq.gsfc.nasa.gov/omps/ for more details). NPP is the National Polar-orbiting Partnership satellite (NPP) and is a partnership is between NASA, NOAA and DoD (Department of Defense), see http://npp.gsfc.nasa.gov/ for more details.

The Equivalent Effective Stratospheric Chlorine (EESC) data used in this report are calculated using observations of ozone depleting substances (ODS) from the Advanced Global Atmospheric Gases Experiment (AGAGE). AGAGE is supported by MIT/NASA (all sites); Australian Bureau of Meteorology and CSIRO (Cape Grim, Australia); UK Department of Energy and Climate Change (DECC) (Mace Head, Ireland); National Oceanic and Atmospheric Administration (NOAA) (Ragged Point, Barbados); Scripps Institution of Oceanography and NOAA (Trinidad Head, USA; Cape Matatula, American Samoa). The authors would like to thank all the staff at the AGAGE global stations for their diligent work in collecting AGAGE ODS data

This research is carried out under contract from Australian Government Department of the Environment to CSIRO.

The 2015 Antarctic Ozone Hole Summary: Final Report | v

http://npp.gsfc.nasa.gov/

http://ozoneaq.gsfc.nasa.gov/omps/

http://ozonewatch.gsfc.nasa.gov/meteorology/SH.html

1 Satellite data used in this reportFull information on the satellite instruments mentioned below can be found on the following NASA website:https://ozoneaq.gsfc.nasa.gov/missions Below is a summary of the instruments, satellite platforms and resultant data that are used in this report.

1.1 TOMS

The Total Ozone Mapping Spectrometers (TOMS) were a series of 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. The TOMS instruments flew on a series of satellites: Nimbus 7 (24 Oct 1978 until 6 May 1993); Meteor 3 (22 Aug 1991 until 24 Nov 1994); and Earth Probe (2 July 1996 until 14 Dec 2005). The version of TOMS data used in this report have been processed with the NASA TOMS Version 8 algorithm.

1.2 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, were utilized again in the 2014 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 data were reprocessed by CSIRO, which at the time resulted in small changes in the ozone hole metrics we calculate.

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.

1.3 OMPS

OMPS (Ozone Mapping and Profiler Suite) is a new set of ozone instruments on the Suomi National Polar-orbiting Partnership satellite (Suomi NPP), which was launched on 28 October 2011 and placed into a sun-

The 2015 Antarctic Ozone Hole Summary: Final Report | 1

https://ozoneaq.gsfc.nasa.gov/missions

synchronous orbit 824 km above the Earth (http://ozoneaq.gsfc.nasa.gov/omps/). 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 2015 ozone hole season, we also used 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.

2 | The 2015 Antarctic Ozone Hole Summary: Final Report

http://npp.gsfc.nasa.gov/

http://ozoneaq.gsfc.nasa.gov/omps/

2 The 2015 Antarctic ozone hole

2.1 Ozone hole metrics

Figure 1 shows the Antarctic ozone hole ‘depth’, which is the daily minimum ozone (DU) observed south of 35°S throughout the season. What can be noted is that the onset of the 2015 ozone hole was later than usual, with the OMI ozone minima not dropping below 220 DU until 18 August. This was the latest onset of the ozone hole since the mid-to-late 1980s. The OMPS minima did fall below 220 DU on 3, 5 & 6 August due to a few ‘pixels’ right at the polar night edge reaching just below this threshold. 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 August. The daily ozone minima continued to be quite variable during the fourth week of August through to the third week of September, at which point it had dropped to 145 DU on 18 September, close to the long-term 1979-2014 average for that time of year. By this time the large variability in this metric had reduced significantly due to the ozone hole completely enclosing the polar region and the polar night having reduced considerably.

Figure 1. Ozone hole ‘depth’ (minimum ozone, DU) based on OMI & OMPS satellite data. The 2015 hole based on OMI data is indicated by the thick black line while the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean.

The ozone minima continued to drop during the last two weeks of September and first week of October, reaching 101 DU on 4 October (this is the 2015 minima from OMI) before rising slightly to 109 DU on 6 October and then back to 103 DU on 8 October. The second week of October saw the ozone hole minima from OMI plateau, with the average across the first half of October being around 107 DU. Interestingly, the OMPS ozone hole minima dropped to 95 DU on 8 October (this is the 2015 minima from OMPS) and remained around there until 12 October, which is considerably lower than what is seen by OMI. Based on the minima from OMPS, then this years’ hole would rank equal (with 2011) 8 th lowest on record. The ozone hole minima essentially plateaued for the period from 4-27 October, only increasing slightly during this time. This resulted in the ozone minima on 23 & 24 October being the lowest on record for this time of year, at 1-3 DU lower than the previous minima.


Following this the ozone minima began to increase again, and at times tracked along the edge of the previous lowest minima, before increasing sharply to 154 DU on 10 November. The ozone minima then entered another period where it was relatively ‘flat’ (approximately between 145-160 DU) from 10 November until 9 December, after which it increased sharply to about 200 DU by mid-December and recovering above 220 DU by 21 December. The period from 4-10 December was the lowest on record for this time of year, with the difference from the previous lowest minima on 7 December being 25 DU. Overall, this resulted in the 2015 ozone hole being relatively deep; the minimum ozone level recorded in 2015 was the 12th deepest hole recorded (out of 36 years of TOMS/OMI satellite data, see table1) based on OMI data, or equal (with 2011) 8th lowest based on OMPS data. The deepest hole ever was in 2006 (85 DU), the second deepest in 1998 (86 DU) and the 3rd deepest in 2000 (89 DU).

Figure 2 shows the average amount of ozone (DU) within the Antarctic ozone hole throughout the 2015 season. The minimum average ozone within the hole in 2015 was 157 DU during the second week of October, the 16th lowest ever recorded, indicating a ‘middle of the pack’ ozone hole based on this metric. The lowest reading was in 2000 (138 DU), the second lowest in 2006 (144 DU) and the 3 rd lowest in 1998 (147 DU).

Figure 2. Average amount (DU) of ozone within the Antarctic ozone hole throughout the season based on OMI & OMPS satellite data. The 2015 hole based on OMI data is indicated by the thick black line; the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean.

Figure 3 shows the Antarctic ozone hole area (defined as the area within the 220 DU contour) throughout the 2015 season. The maximum daily area of the hole (28.1 million km2 in the first week of October) was the 4th largest hole on record, with the largest in 2000 (29.8 million km2), the 2nd largest in 2006 (29.6 million km2) and the 3rd largest in 2003 (28.4 million km2). The maximum in the 15-day average ozone hole area for 2015 was 27.55 million km2, the 3rd largest area ever recorded, with the largest in 2000 (28.7 million km2) and second largest in 2006 (27.56 million km2). These statistics indicate that the 2015 ozone hole, in terms of areal extent, was very large. However, what is even more remarkable is the amount of time during October, November and December that the 2015 ozone hole area was at unprecedented record levels above any previously seen maximums. Specifically, for the whole period from 28 September through to 4 November, the 2015 ozone hole was higher than any previously record maximums, by up to 4 million km2. This was the case again for the periods of 7-9 November, 12-24 November, and lastly 1-7


December. The 2015 ozone hole has now redefined much of the maximum envelope indicated by the grey shading in Fig. 3.

Figure 3. Ozone hole area based on OMI & OMPS satellite data. The 2015 hole based on OMI data is indicated by the thick black line while the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean.

Figure 4 shows the daily (24 hour) maximum ozone deficit in the Antarctic ozone hole, which is a function of both ozone hole depth and area. This metric is not the amount of ozone lost within the hole each day, but is a measure of the accumulated loss summed over the lifetime of ozone within the hole as measured each day. The maximum daily ozone deficit in 2015 was 37.7 million tonnes (Mt) in the second week of October, the 7th largest deficit ever, again indicating quite a large ozone hole compared with the other 35 years of satellite records; the largest was in 2006 (45.1 Mt). Similar to the ozone hole area, there were several periods where this metric set new record levels above any previously seen maximums, as can be seen in Figure 2.

Integrated over the whole ozone-hole season, the total ozone deficit (the sum of the daily ozone deficits) was about 2197 Mt of ozone in 2015 (2145 Mt based on OMPS), the 5 th largest cumulative ozone deficit ever recorded, the largest was in 2006 (2560 Mt).

Apart from some small discrepancies in the ozone column minima and ozone hole area, in general the ozone hole metrics presented here based on the OMI and OMPS records compare very well, as can be seen in Figures 1-4. This continues to be an encouraging result and gives confidence that the OMPS instrument can seamlessly continue the long-term OMI/TOMS ozone hole records.


Figure 4. OMI & OMPS estimated daily ozone deficit (in millions of tonnes, Mt) within the ozone hole. The 2015 hole based on OMI data is indicated by the thick black line while the light blue line indicates the 2015 hole based on OMPS data. The holes for selected previous years 1998, 2000, 2003, 2006 & 2014 are indicated by the thin orange, blue, red, green and pink lines respectively; the grey shaded area shows the 1979-2014 TOMS/OMI range and mean. The estimated total (integrated) ozone loss for each year is shown in the legend.

2.2 Total column ozone images

The daily total column ozone data over Australia and Antarctica for September through to December 2015 from OMI are shown in Appendix A Figures A.1, A.2, A.3 and A.4 respectively; and images from OMPS for September through to December 2015 are shown in Appendix A Figures A.5, A.6, A.7 and A.8 respectively.

The formation of the 2015 ozone hole can be clearly seen in the images from 1 through to 13 September, as the red 220 DU contour progressively grew during this period until it was completely closed on 14 September. The polar night is clearly visible in the images for September, with it successively reducing each day until it had completely disappeared by 1 October.

The most prominent feature that can be seen in the daily images is how remarkably symmetrical and stable the ozone hole was during 2015, indicating a lack of wave activity and a very stable polar vortex. The stable conditions persisted essentially from mid-September through to early December, which was quite unusual. During this period there were perhaps three occasions where the ozone hole underwent some small instabilities. These were 29 September to 1 October, 2 to 11 November, and 15 to 19 November, however the size of the distortions were relatively small. While the size and depth of the ozone hole reduced in late November and early December, it wasn’t until about 6 December that the ozone hole/polar vortex became unstable leading to the breakup of the hole and full recovery by 21 December.

In previous years, one of the dominant features in the daily images has been a strong ridge of high ozone in the band immediately south of Australia between about 40-60S, which was almost absent or greatly reduced during 2015 and again is quite unusual compared to most previous years.

The highly stable ozone hole and polar vortex meant that the three Australian Antarctic stations of Mawson, Davis and Casey were essentially inside the ozone hole for much of September and October, and it wasn’t until November that there were significant periods when the three stations were outside of the ozone hole due to the above mentioned instabilities.


2.3 Antarctic meteorology/dynamics

The 2015 MERRA 45-day mean 45-75°S heat fluxes at 50 & 100 hPa are shown in the left hand panels of 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 activity) and results in a warming of the polar vortex. The corresponding 60-90°S zonal mean temperatures at 50 & 100 hPa for 2015 are shown in the right hand panels of Figure 5, these usually show an anti-correlation to the heat flux.

During June the 45-75S 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. Correspondingly, the 60-90 S zonal mean temperatures at 50 & 100 hPa were, overall, similar to the 1979-2014 average, with some deviations above and below this line in June & July.

By the end 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 10 th percentile mark of the 1979-2014 range, both continuing to indicate reduced heat transport towards the pole. For much of August, the 60-90 S zonal mean temperatures at both 50 & 100 hPa were below the 30 th percentile mark of the 1979-2014 range, indicating relatively cold temperatures.

The first thirteen days of September saw the 45-75S heat flux at 50 & 100 hPa either exceed the maximum seen for the 1979-2014 range for this time of year or be in the highest 10 th percentile mark of the 1979-2014 range, both continuing to indicate reduced heat transport towards the pole. The 60-90 S zonal mean temperatures during this period at both the 50 & 100 hPa levels remained quite cold either in the lower 10-30% percent mark of the 1979-2014 range or just inside the lower 30-50% mark of the 1979-2014 range. By 25 September the heat flux indicated increased transport of heat towards the pole, but still in the 10 th

percentile range (significantly less polar heat transport than the long term average), where it remained until the end of September. By 25 September and through to the end of September the zonal mean temperatures at 50 and 100 hPa were at record lows for this time of the year – again a sign of a very stable (cold) vortex.

The 45-75S heat flux at both the 50 & 100 hPa levels more or less remained in the highest 10 th percentile mark of the 1979-2014 range during all of October. This resulted in record low 60-90 S zonal mean temperature at both the 50 & 100 hPa levels, with the 100 hPa level recording significantly lower temperatures than any previous minima during 1979-2014. These very cold temperatures contributed to the very stable polar vortex seen during this period.

The 45-75S heat flux for December at both the 50 & 100 hPa levels tracked into, and remained in, the highest 10-30th percentile bracket of the 1979-2014 range, indicating heat transport towards the pole, which ultimately contributed to the breakup of the 2015 ozone hole. Correspondingly, the 60-90 S zonal mean temperatures at both the 50 & 100 hPa levels remained in the lowest 10 th percentile of the long-term 1979-2014 range for the first half of December, before moving into the lowest 10-30 th percentile range of the long-term 1979-2014 means during the second half of December.

At 50 hPa, the type 1 PSC (HNO3.3H2O) formation threshold temperature (195 K) was reached in late June, staying below the threshold until mid-September. At 100 hPa, the threshold temperature was reached during the second week of July and remain below the threshold on 25 September.


Figure 5. NASA MERRA heat flux and temperature. The 45-day mean 45°S-75°S eddy heat flux at 50 and 100 hPa are shown in the two left hand panels. The 60°S-90°S zonal mean temperature at 50 & 100 hPa are shown in the right two panels. Images courtesy of NASA GSFC – http://ozonewatch.gsfc.nasa.gov/meteorology/SH.html.


http://ozonewatch.gsfc.nasa.gov/meteorology/SH.html

3 Comparison to historical metricsTable 1 contains the ranking for all 36 ozone holes recorded since 1979 for the various metrics that measure the ‘size’ of the Antarctic ozone hole: 1 = lowest ozone minimum, greatest area, greatest ozone loss etc.; 2 = second largest….

The definitions of the various metrics are:

Daily ozone hole area is the maximum daily ozone hole area on any day during ozone hole season.

15-day average ozone hole area is based on a 15-day moving average of the daily ozone hole area.

Ozone hole depth (or daily minima) is based on the minimum column ozone amount on any day during ozone hole season.

The 15-day average ozone hole depth (or minima) is based on a 15-day moving average of the daily ozone hole depth.

Minimum average ozone is the minimum daily average ozone amount (within the hole) on any day during ozone hole season.

Daily maximum ozone deficit is the maximum ozone deficit on any day during ozone hole season.

Ozone deficit is the integrated (total) ozone deficit for the entire ozone hole season.

From Table 1 it can be seen that the 2015 ozone hole was one of the largest holes in terms of areal extent with it ranking 3rd and 4th in the area metrics, and 5th & 7th in the ozone deficit metrics. The 2015 ozone hole was only of average depth with it ranking 12 th & 16th in the minima metrics. These are comparisons from 36 years of TOMS/OMI satellite records.


Table 1. Antarctic ozone hole metrics based on TOMS/OMI satellite data - ranked by size or minima (Note: 2005 metrics are average of TOMS and OMI data).

15-DAY AVERAGEOZONE HOLE AREA

DAILY OZONE HOLEAREA MAXIMA

15-DAY AVERAGEOZONE HOLE MINIMA

OZONE HOLEDAILY MINIMA

DAILY MINIMUMAVERAGE OZONE

DAILY MAXIMUMOZONE DEFICIT

INTEGRATED OZONEDEFICIT

RANK YEAR 106 KM2 YEAR 106 KM2 YEAR DU YEAR DU YEAR DU YEAR MT YEAR MT1 2000 28.7 2000 29.8 2000 93.5 2006 85 2000 138.3 2006 45.1 2006 25602 2006 27.6 2006 29.6 2006 93.7 1998 86 2006 143.6 2000 44.9 1998 24203 2015 27.6 2003 28.4 1998 96.8 2000 89 1998 146.7 2003 43.4 2001 22984 2003 26.9 2015 28.1 2001 98.9 2001 91 2003 147.5 1998 41.1 1999 22505 1998 26.8 1998 27.9 1999 99.9 2003 91 2005 148.8 2008 39.4 2015 21976 2008 26.1 2005 27.0 2011 100.9 2005 93 2001 148.8 2001 38.5 1996 21767 2001 25.7 2008 26.9 2003 101.9 1991 94 1999 149.3 2015 37.7 2000 21648 2005 25.5 1996 26.8 2005 102.8 2011 95 2009 150.4 2005 37.7 2011 21249 2011 25.1 2001 26.4 2009 103.1 2009 96 1996 150.6 2011 37.5 2008 1983

10 1996 25.0 2011 25.9 1993 104.0 1999 97 2008 150.8 2009 35.7 2005 189511 1993 24.8 1993 25.8 1996 106.0 1997 99 2011 151.2 1999 35.3 2003 189412 1994 24.3 1999 25.7 2015 107.1 2015 101 1997 151.3 1997 34.5 1993 183313 2007 24.1 1994 25.2 1997 107.2 2004 102 2007 155.1 1996 33.9 2009 180614 2009 24.0 2007 25.2 2008 108.9 2008 102 1993 155.2 1992 33.5 2007 177215 1992 24.0 1997 25.1 1992 111.5 1996 103 1992 156.3 2007 32.9 1997 175916 1999 24.0 1992 24.9 2007 112.7 1993 104 2015 156.9 1993 32.6 1992 152917 1997 23.3 2009 24.5 1991 113.4 1992 105 2014 160.0 2014 30.7 1987 136618 2013 22.7 2013 24.0 1987 115.7 2007 108 1991 162.5 1991 26.6 2010 135319 2014 22.5 2014 23.9 2004 116.0 1989 108 1987 162.6 2010 26.2 2014 125220 2010 21.6 2004 22.7 1990 117.8 1987 109 1990 164.4 1987 26.2 1990 118121 1987 21.4 1987 22.4 1989 120.4 1990 111 2010 164.5 2013 25.1 2013 103722 2004 21.1 1991 22.3 2014 124.3 2014 114 2013 164.7 1990 24.3 1991 99823 1991 21.0 2010 22.3 2010 124.3 2013 116 1989 166.2 1989 23.6 2004 97524 1989 20.7 2002 21.8 2013 127.8 2010 119 2004 166.7 2002 23.2 1989 91725 1990 19.5 1989 21.6 1985 131.8 1985 124 2002 169.8 2004 22.8 2012 72026 2012 19.3 2012 21.2 2012 131.9 2012 124 2012 170.2 2012 22.5 1985 63027 2002 17.7 1990 21.0 2002 136.0 2002 131 1985 177.1 1985 14.5 2002 57528 1985 16.6 1985 18.6 1986 150.3 1986 140 1986 184.7 1986 10.5 1986 34629 1986 13.4 1984 14.4 1984 156.1 1984 144 1984 190.2 1984 9.2 1984 25630 1984 13.0 1986 14.2 1983 160.3 1983 154 1983 192.3 1983 7.0 1988 19831 1988 11.3 1988 13.5 1988 169.4 1988 162 1988 195.0 1988 6.0 1983 18432 1983 10.1 1983 12.1 1982 183.3 1982 170 1982 199.7 1982 3.7 1982 7333 1982 7.5 1982 10.6 1980 200.0 1980 192 1980 210.0 1980 0.6 1980 1334 1980 2.0 1980 3.2 1981 204.0 1979 194 1979 210.2 1981 0.6 1981 435 1981 1.3 1981 2.9 1979 214.7 1981 195 1981 210.2 1979 0.3 1979 1


36 1979 0.2 1979 1.2 1994 NaN 1994 NaN 1994 NaN 1994 NaN 1994 NaN


Figure 6 shows the 15-day moving average of the minimum daily column ozone levels recorded in the hole since 1979 from TOMS and OMI data. This metric shows a consistent downward trend in ozone minima from the late 1970s until the mid-to-late-1990s, with signs of ozone recovery by 2015. The 1996-2001 mean was 100±5 DU, while the 2010-2015 mean was 119±12 DU. There is a strong suggestion that ozone is recovering with the uncertainties no longer overlapping (at 1σ level). The 2015 ozone hole is ranked the twelfth lowest for this metric.

The orange line in Figure 6 (and in Figures 7, 8, 9 and 10) is a simple linear regression of Antarctic Equivalent Effective Stratospheric Chlorine (EESC-A; 5.5 year lag) against the 15-day smoothed column minima (and the other metrics in Figures 7, 8, 9 and 10), plotted against time. EESC is calculated from Cape Grim data – both in situ and from the Cape Grim Air Archive – and AGAGE global measurements of Ozone Depleting Substances (ODSs: chlorofluorocarbons, hydrochlorofluorocarbons, halons, methyl bromide, carbon tetrachloride, methyl chloroform and methyl chloride (Fraser et al., 2014)). The regressed EESC broadly matches the decadal variations in the ozone minima indicating a slow recovery since early to mid-2000s. It also gives a guide to the relative importance of the meteorological variability, especially in recent years.

Figure 6. Minimum ozone levels observed in the Antarctic ozone hole using a 15-day moving average of the minimum daily column ozone levels during the entire ozone season for all available years of TOMS (green) and OMI (purple) data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text. The error bars represent the range of the daily ozone minima in the 15-day average window.

If we simply remove the significantly dynamically-influenced 2002 ozone data from Figure 6, the remaining data (1996-2015) show signs of ozone growth (recovery) of 1.1±0.4 (1σ) DU/yr.

Figure 7 shows the average ozone amount in the ozone hole (averaged column ozone amount in the hole weighted by area) from 1979 to 2015 from TOMS and OMI data. This metric shows a consistent downward trend in average ozone from the late-1970s until the late-1990s, with some sign of ozone recovery by 2015. The 1996-2001 mean was 148±5 DU while the 2010-2015 mean was 161±7 DU. There is now a strong suggestion that ozone is recovering with the uncertainties no longer overlapping (at 1σ level) for this metric.

If we remove the significantly dynamically-influenced 2002 and 2004 ozone data from Figure 7, the remaining data (1996-2015) show signs of ozone growth (recovery) of 0.8±0.2 (1σ) DU/yr. This is also indicated by the regressed EESC-A line.


Figure 7. The average ozone amount in the ozone hole (averaged column ozone amount in the hole weighted by area) for all available years of TOMS (green) and OMI (purple) data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text.

Figure 8 shows the maximum ozone hole area (15-day average) recorded since 1979 from TOMS and OMI data. Disregarding the unusual years (1988, 2002, 2004) when the polar vortex broke up early, this metric suggests that the ozone hole has stopped growing around the year 2000 (date of maximum ozone hole area), and may now be showing signs of a decline in area, with the exception that 2015 is now an outlier. The 1996-2001 mean was (25.6±2.0) x106 km2, while the 2010-2015 mean was (23.1±2.9) x106 km2, indicative of the commencement of possible ozone recovery, but not statistically significant.

If we remove the significantly dynamically-influenced 2002 and 2004 ozone data from Figure 8, the remaining data (1996-2015) are starting to show a decrease in ozone hole area of (0.14±0.09) x106 km2/yr.

Figure 8. Maximum ozone hole area (area within the 220 DU contour) using a 15-day moving average during the ozone hole season, based on TOMS data (green) and OMI data (purple). The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text. The error bars represent the range of the ozone hole size in the 15-day average window.

Figure 9 shows the integrated ozone deficit (Mt) from 1979 to 2015. The ozone deficit rose steadily from the late-1970s until the late-1990s/early 2000s, where it peaked at approximately 2300 Mt, and then started to drop back down. This metric is very sensitive to meteorological variability; however, if we exclude the 2002 data (when the ozone hole split in two due to a significant dynamical disturbance) then there appears to be evidence of ozone recovery. The 1996-2001 mean was 2180±230 Mt while the 2010-2015 mean was 1445±595 Mt, indicative of the commencement of possible ozone recovery, but not statistically significant.


If we remove the significantly dynamically-influenced 2002 ozone data from Figure 9, the remaining data (1996-2014) show signs of a decline in ozone deficit of 42±18 (1σ) Mt/yr.

Figure 9. Estimated total ozone deficit for each year in millions of tonnes (Mt), based on TOMS (green) and OMI (purple) satellite data. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text.

The most quoted (though not necessarily the most reliable) metric in defining the severity of the ozone hole is the average minimum ozone levels observed over Halley Station (British Antarctic Survey), Antarctica, throughout October (Figure 10). This was the metric that was first reported in 1985 to identify the significant ozone loss over Antarctica. Based on this metric alone, it would appear that October mean ozone levels over Halley may have started to increase again. The minimum ozone level was observed in 1993, which has been attributed to residual volcanic effects (Mt Pinatubo, 1991). Ignoring the warm years of 2002 and 2004, the mean October ozone levels at Halley Station for 2010 to 2015 (161±21 DU) are higher than those observed from 1996 to 2001 (141±4 DU), indicative of the commencement of possible ozone recovery, but not statistically significant.

If we remove the significantly dynamically-influenced 2002 and 2004 ozone data from Figure 10, the remaining data (1996-2015) show significant ozone growth (recovery) of 1.1±0.6 (1σ) DU/yr. For the period 1993-2015 the ozone growth is 1.5±0.4 (1σ) DU/yr, although the early 1990s data may be low due to the impact of the Mt Pinatubo eruption.

Figure 10. Total column ozone amounts (October mean) as measured at Halley Station, Antarctica, by the British Antarctic Survey from 1956 to 2015. The orange line is obtained from a linear regression to Antarctic EESC (EESC-A) as described in the text.


4 Antarctic ozone recoveryOzone recovery over Antarctica is complex to model. Apart from the future levels of ozone depleting chlorine and bromine in the stratosphere, temperature trends and variability in the stratosphere, the impact of major volcanic events and the future chemical composition (for example H 2O, CH4 and N2O) of the stratosphere are likely to be important factors in determining the rate of ozone recovery. Model results and observations show that the solar cycle changes have maximum impact on tropical ozone and do not significantly impact on stratospheric ozone levels over Antarctica.

Equivalent Chlorine (ECl: chlorine plus weighted bromine) levels, derived from CSIRO Cape Grim and other AGAGE surface and CSIRO Antarctic firn observations of ODSs, are likely to decline steadily over the next few decades at about 1% per year, leading to reduced ozone destruction. Figure 11 shows Equivalent Effective Stratospheric Chlorine for mid- (EESC-ML) and Antarctic (EESC-A) latitudes, derived from ECl using fractional release factors from Newman et al. (2007), lagged 3 years (EESC-ML) and 5.5 years (EESC-A) to approximate the time taken to transport ECl to these regions of the stratosphere.

EESC-A peaked at 4.2 ppb in 2000 and EESC-ML at 1.97 ppb in 1998 respectively, falling to 3.79 and 1.66 ppb respectively by 2015, declines of 9.8% and 15.7% respectively. Table 2 shows the species contributing to the declines in EESC-A (~0.41 ppb) and in EESC-ML (~0.32 ppb) since their peak values in 2000 and 1998 respectively. The decline since 2000/1998 to 2015 is dominated by methyl chloroform, followed by methyl bromide, the CFCs and carbon tetrachloride. The halons and HCFCs have made an overall growth contribution to EESC-A and EESC-ML since 2000/1998.

Table 2. ODS contributions to the decline in EESC at Antarctic and mid-latitudes (EESC-A, EESC-ML) observed in the atmosphere in 2015 since their peak values in 2000 and 1998 respectively.

Species EESC declineAntarctic

ppb Cl

EESC declinemid-latitudes

ppb Cl

methyl chloroform 0.28 0.20methyl bromide 0.13 0.09CFCs 0.09 0.05carbon tetrachloride 0.06 0.04halons -0.08 -0.03HCFCs -0.07 -0.03Total decline 0.41 0.32

The initial (1-2 decades) decline in EESC-ML and EESC-A have been and will be dominated by the shorter-lived ODSs, such as methyl chloroform and methyl bromide, whereas the long-term decline will be dominated by CFCs and carbon tetrachloride. Based on EESC-ML and EESC-A values from scenarios of ODS decline (Harris and Wuebbles, 2014), ozone recovery at mid-latitudes will occur at about the mid- to late-2040s and ozone recovery in the Antarctic stratosphere will occur about the mid-2070s. This is now a few years later than reported in the previous ozone assessment due to the updated longer estimated lifetimes for CFC-11 and CCl4. These lead to slower atmospheric decay and thus an increased contribution to EESC in the future.

In response to the need to easily convey information to the general public about the levels of ozone-destroying chemicals in the atmosphere, and when might the ozone hole recover, NOAA has developed the Ozone Depleting Gas Index (ODGI) (Hoffman and Montzka, 2009; and recent updates see http://www.esrl.noaa.gov/gmd/odgi/). The index neatly describes the state of the atmosphere, in relation to stratospheric halogen (chlorine plus bromine) levels, and is based on atmospheric measurements of ODSs. The index has two components, one relevant for ozone-depleting chemicals and the ozone hole over


http://www.esrl.noaa.gov/gmd/odgi/

Antarctica (the ODGI-A), and one relevant for mid-latitudes (the ODGI-ML). Figure 12 shows the CSIRO version of the ODGI-ML and ODGI-A indices derived from global AGAGE data including data from Cape Grim. Based on data up to 2015, the ODGI-A and ODGI-ML indices have declined by 19% and 39% respectively since their peak values in 2000 and 1998 respectively, indicating that the atmosphere in 2015 is 19% and 39% along the way toward a halogen level that should allow an ozone-hole free Antarctic stratosphere and a ‘normal’ (pre-1980s) ozone layer at mid-latitudes. The CSIRO version of the ODGI uses ODS fractional release factors from Newman et al. (2007).

Figure 11. Equivalent Effective Stratospheric Chlorine for mid-and Antarctic latitudes (EESC-ML, EESC-A) derived from global measurements of all the major ODSs at Cape Grim (CSIRO) and other AGAGE stations and in Antarctic firn air (CSIRO) from Law Dome. EESC-A is lagged 5.5 years and EESC-ML 3 years to approximate the transport times for ODSs from the Earth’s surface (largely in the Northern Hemisphere) to the stratosphere at Southern Hemisphere mid- and Antarctic latitudes. Arrows indicate dates when the mid-latitude and Antarctic stratospheres return to pre-1980s levels of EESC, and approximately pre-ozone hole levels of stratospheric ozone.


Figure 12. ODGI-A and ODGI-ML indices (Hofmann and Montzka, 2009) derived from AGAGE ODS data using ODS fractional release factors from Newman et al. (2007).


Summary The 2015 Antarctic ozone hole was relatively large compared to holes from the past 35+ years. The

most prominent feature of the 2015 Antarctic ozone hole was how remarkably symmetrical and stable it was, indicating a lack of wave activity and a very stable polar vortex. This was due, in part, to a record low temperatures in the mid to low stratosphere for extended period of time during the ozone hole season. Another feature was the lack of a high ridge of ozone immediately to the south of the Australian mainland, which for most years is a usual feature.

In terms of areal extent, the 2015 hole ranked 3rd or 4th largest ever, depending on the metric used, and for extended periods of time (especially all of October 2015), set new records for the daily maximum extent for that time of year compared with all previous ozone holes. For the ozone deficit, the 2015 hole similarly ranked quite high, being the 5 th largest in terms of integrated ozone loss and 7th largest in terms of daily ozone deficit. However, in terms of ozone hole minima, the 2015 hole was of only average ‘depth’, ranking 12 th lowest for daily minima and 16th lowest for the average amount of ozone within the hole.

The 2000 and 2006 ozone holes were the largest ozone holes ever, depending on the metric that is used.

Most ozone metrics discussed in this report show signs that ozone recovery has commenced, once the influence of the severely dynamically-impacted ozone data (in particular from 2002 and 2004) are removed from the ozone record.

Comparison of trends in EESC and cumulative ozone deficit within the hole since the late 1970s suggest that ozone recovery may have commenced.

The EESC data from observations and future scenarios suggest that ozone recovery at mid-latitudes will occur at about the mid- to late-2040s and Antarctic ozone recovery at about the mid-2070s.

The ODGI values suggest that the atmosphere, by 2014, is about 19% along the path to Antarctic ozone recovery and 39% along the path to ozone recovery at mid-latitudes.

Changes in EESC-A and changes in ozone over Antarctica (satellite and Dobson) are highly correlated and the Dobson data at Halley Station suggest Antarctic ozone recovery has commenced. The correlation could be even more significant if temperature effects were removed from the ozone data.

Animations of the daily images from the 2015 ozone hole (along with previous years’ holes) in various video formats can be downloaded from ftp://gaspublic:[email protected]/pub/ozone_hole/.

Animations of the historical October 1-15 averages for all available years in the period 1979-2015 are also contained in this directory. To download, right click the file and select ‘Copy to folder …’.


ftp://gaspublic:[email protected]/pub/ozone_hole/

Appendix A 2015 daily total column ozone imagesAvailable separately upon request


DefinitionsAGAGE: Advanced Global Atmospheric Gases Experiment; AGAGE, and its predecessors (the Atmospheric Lifetime Experiment, ALE, and the Global Atmospheric Gases Experiment, GAGE) have been measuring the composition of the global atmosphere continuously since 1978. AGAGE measures over the globe, at high frequency, almost all of the important trace gas species in the Montreal Protocol (e.g. CFCs and HCFCs) and almost all of the significant non-CO2 gases in the Kyoto Protocol (e.g. PFCs, HFCs, methane, and nitrous oxide). See http://agage.eas.gatech.edu/index.htm for more details.

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).

ODS: Ozone Depleting Substances (chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, methyl chloroform and methyl chloride).

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 & OMPS: the Total Ozone Mapping Spectrometer, Ozone Monitoring Instrument, & Ozone Mapping and Profiler Suite, are satellite borne instruments that measure the amount of back-scattered


http://agage.eas.gatech.edu/index.htm

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.


References Dameris, M., and S. Godin-Beekmann (Lead Authors), S. Alexander, P. Braesicke, M. Chipperfield, A.T.J. de

Laat, Y. Orsolini, M. Rex, and M.L. Santee, Update on Polar ozone: Past, present, and future, Chapter 3 in Scientific Assessment of Ozone Depletion: 2014, Global Ozone Research and Monitoring Project – Report No. 55, World Meteorological Organization, Geneva, Switzerland, 2014.

Fraser, P. J., P. B. Krummel, L. P. Steele, C. M. Trudinger, D. M. Etheridge, S. O'Doherty, P. G. Simmonds, B. R. Miller, J. Muhle, R. F. Weiss, D. Oram, R. G. Prinn, and R. Wang, Equivalent effective stratospheric chlorine from Cape Grim Air Archive, Antarctic firn and AGAGE global measurements of ozone depleting substances, Baseline Atmospheric Program (Australia) 2009-2010, N. Derek P. B. Krummel and S. J. Cleland (eds.), Australian Bureau of Meteorology and CSIRO Marine and Atmospheric Research, Melbourne, Australia, 17-23, 2014.

Harris, N. R. P., and D. J. Wuebbles (Lead Authors), J. S. Daniel, J. Hu, L. J. M. Kuijpers, K. S. Law, M. J. Prather, and R. Schofield, Scenarios and information for policymakers, Chapter 5 in Scientific Assessment of Ozone Depletion: 2014, Global Ozone Research and Monitoring Project – Report No. 55, World Meteorological Organization, Geneva, Switzerland, 2014.

Hassler, B., J. S. Daniel, B. J. Johnson, S. Solomon and S. J. Oltmans, An assessment of changing ozone loss rates at South Pole: Twenty-five years of ozonesonde measurements, J. Geophys. Res., 116, D22301, doi:10.1029/2011JD016353, 2011a.

Hassler, B., G. E. Bodeker, S. Solomon and P. J. Young, Changes in the polar vortex: Effects on Antarctic total ozone observations at various stations, Geophys. Res. Letts., 38, L01805, doi:10.1029/2010GL045542, 2011b.

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Kramarova, N. A., E. R. Nash, P. A. Newman, P. K. Bhartia, R. D. McPeters, D. F. Rault, C. J. Seftor, P. Q. Xu and G. J. Labow, Measuring the Antarctic ozone hole with the new Ozone Mapping and Profiler Suite (OMPS), Atmos. Chem. Phys., 14, 2353–2361, doi:10.5194/acp-14-2353-2014, 2014.

Kuttippurath, J., F. LeFevre, J.-P. Pommereau, H. K. Roscoe, F. Goutail, A. Pazmino and J. D. Shanklin, Antarctic ozone loss in 1979-2010: first sign of ozone recovery, Atmos. Chem. Phys., 13, 1625-1635, doi:10.5194/acp-13-1625-2013, 2013.

Miyagawa, K., I. Petropavlovskikh, R. D. Evans, C. Long, J. Wild, G. L. Manney and W. H. Daffer, Atmos. Chem. Phys., 14, 3945-3968, doi:10.5194/acp-14-3945-2014, 2014.

Newman, P. A., E. R. Nash, S. R. Kawa, S. A. Montzka and S. M. Schauffer, When will the Antarctic ozone hole recover? Geophys. Res. Letts., 33, L12814, doi:10.1029/2005GL025232, 2006.

Newman, P., J. Daniel, D. Waugh & E. Nash, A new formulation of equivalent effective stratospheric chlorine (EESC), Atmos. Chem. Phys., 7, 4537-4552, 2007.

Salby, M., E. Titova & L. Deschamps, Rebound of Antarctic ozone, Geophys. Res. Letts., 38, L09702, doi:10.1029/2011GL047266, 2011.

Salby, M., E. Titova and L. Deschamps, Changes of the Antarctic ozone hole: controlling mechanisms, seasonal predictability and evolution, J. Geophys. Res., 117, D10111, doi:10.1029/2011JD016285, 2012.


Strahan, S. E., A. R. Douglass, P. A. Newman, and S. D. Steenrod, Inorganic chlorine variability in the Antarctic vortex and implications for ozone recovery, J. Geophys. Res. Atmos., 119, 14098–14109, doi:10.1002/2014JD022295, 2014.


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