The 2010 Antarctic Ozone Hole Summary: Tuesday 11 January 2011
Paul Krummel and Paul Fraser
Centre for Australian Weather and Climate Research
CSIRO Marine & Atmospheric Research
Aspendale, Victoria
Instrumentation
Data from the Ozone Monitoring Instrument (OMI) on board the Earth Observing Satellite (EOS) Aura, that have been processed with the NASA TOMS Version 8.5 algorithm, will be utilized again this year in our weekly ozone hole reports. OMI continues the NASA TOMS satellite record for total ozone and other atmospheric parameters related to ozone chemistry and climate.
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. 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, leading to the larger stripes of bad data that are seen in current OMI images. Affected data have been flagged and removed from the images. NASA thinks that some of the data may be recoverable but a fix may take quite some time to create and test. 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 2010 ozone hole
The OMI data show that the ozone minimum dropped below 220 DU by mid-August, about 1-2 weeks later than in 2005-2009. By the end of August, the ozone minimum in the Antarctic ozone hole had reached about 200 DU, after falling to 165 DU in the third week of August. Approaching the end of the first week of September, the ozone minimum had again reached 165 DU, and stayed at this level through the second week of September. During the third week of September the ozone minimum declined sharply as the vortex at last became more symmetrical (see below), reaching 130 DU by September 25 and just below 120 DU by October 3. By October 10 the ozone minimum had recovered to 130 DU, staying at about that level until October 19. By October 25 the ozone minimum has recovered to 145 DU, similar at this time to 2008 and now more persistent than 2004. By November 1 the ozone minimum had recovered to 150 DU, similar to 2004, and stayed at that level for the 1st 10 days of November, before recovering further to 160 DU by November 14, and approaching 165 DU by November 22. Ozone recovery slowed in late November and throughout December (up to December 12) stayed between 170 and 180 DU. By December 20 ozone had reached over 200 DU, and had fully recovered to above 220 DU by December 22.
The October 3 level (120 DU) was the overall daily minimum for this season. This is currently the weakest minimum ozone hole this past decade, apart from 2002 (Figure 1, top panel).
By the end of August, the ozone hole area was still quite small at less than 5 million km2, but by the first week of September the area rose sharply to 13-14 million km2 (Figure 1, bottom panel), and continued to rise through the second week of September to about 16 million km2, reaching 20 million km2 during the third week of September and 22 million km2 by September 25, falling back to 21 million km2 by October 3, which is similar to 2004, just several weeks later. It reached its maximum area of just over 22 million km2 a few days before the end of September, a few weeks later than usual, very close to Dr A. Klekociuk’s prediction (22 million km2) made at the OSG Meeting on August 9. By October 10 the ozone hole area had declined to close to 19 million km2, declining slowly to 18.5 million km2 by October 19. By October 25 the ozone hole area had further declined to 14 million km2, but by November 1 had recovered to 16.5 million km2. The ozone hole area stayed at about 14-15 million km2 for the first 2 weeks of November, falling to 12.5 million km2 by November 22. At this stage the hole appeared to be similar to what it was at this stage in 2009. However in December the ozone hole area reduction slowed, reaching 8 million km2 by December 12, and 1.5 million km2 by December 20 and down to zero by December 22.
Figure 2 (top panel) shows that the estimated daily ozone deficit by the end of August remained quite low at about 1-3 million tonnes, rising to 5 Mt in the first week of September (less than the past 5 ozone holes), reaching nearly 8 Mt by the end of the second week of September, 16 Mt during the third week of September and 24 Mt by September 25. The deficit reached a maximum of just over 26 Mt on about September 30, declining to 24 Mt by October 3, 21 Mt by October 10, 19 Mt by October 19, 12 Mt by October 25 recovering to 13.5 MT by November 1. The deficit was steady at about this level (12-14 Mt) for the first 10 days of November, declining to 10 Mt by November 15, and 7.5 Mt by November 22. This was significantly more ozone deficit than in 2004 and similar to 2009 at this time. The ozone deficit continued to decline slowly reaching 5 Mt by December 12, the largest ever deficit for this time. By December 22 the ozone deficit was 0 Mt, signalling the end of the hole.
The cumulative ozone loss as of December 20 is about 1340 Mt, greater than the 2004 total loss of 975 Mt, but less than the total ozone loss of 2009 (1810 Mt).
The average ozone amount in the hole (averaged column ozone amount in the hole weighted by area; Figure 2 bottom panel) averaged about 210 DU for the last 2 weeks of August and close to 200 DU by the first week of September, where it has stayed through the second week of September, finally dropping below 200 DU during the third week of September, falling rapidly to 185 DU by September 19, 170 DU by September 25, reaching a likely minimum of 165 DU by the end of September and again on 12 October. By October 19 it had recovered to 175 DU and to over 180 DU by 25 October (similar to 2008 at this time) and to 185 DU by November 1. By November 15, the average ozone amount had recovered to nearly 190 DU and >190 DU by November 22 (now similar to 2009 at this time). In early December the average ozone in the hole was oscillating about 195-200 DU, again the deepest ozone hole ever recorded for this time of the year. By December 22 the average ozone hole minimum had recovered to 220 DU.
Ozone hole metric summary and rankings
The 2010 ozone hole is one of the smallest in the past 15-20 years. Of the 31 holes for which we have data since 1979, the 2010 hole ranked
16th:15-day average area20th: 15-day average minimum ozone
19th: daily maximum area20th: daily minimum ozone
18th:daily ozone deficit18th: daily min average ozone amount in the hole
17th:cumulative ozone loss
This year’s hole can be classified as a late-starter, delayed by the two significant stratospheric warming events of mid-July and early September. These events certainly prevented a much deeper ozone hole from occurring, but the ozone recovery in October-December has been protracted, similar to a deep ozone hole.
Microwave Limb Sounder analyses
Dr A. Klekociuk has provided the following insightful paragraph: In Figure 3, ozone hole area metrics are provided for three partial columns in the lower stratosphere, mid-stratosphere and full stratosphere (denoted as ‘low’, ‘mid’ and ‘full’ partial columns respectively) based on measurements by the Microwave Limb Sounder (MLS) instrument onboard the Aura spacecraft. The MLS instrument provides height-resolved ozone information during day and night, and is thus able to measure the portion of the vortex that is within continuous darkness during winter and spring and inaccessible to the OMI instrument. Figure 3 indicates that ozone depletion in the mid-stratosphere (blue time series) during late winter and early spring of 2010 was less severe and occurred later in comparison to 2009. In contrast, depletion in the lower-stratosphere (red time series) was similar for the two years. The reduced depletion in the mid-stratosphere during 2010 is likely related to the effects of the stratospheric warming and disturbance to the vortex in late July and early August, and contributed to the relatively late formation of the ozone hole and a reduction in its peak size relative to 2009.
Total column ozone images
Total column ozone data over Australia and Antarctica for 1 December – 20 December are shown in Figure 4. The Antarctic polar night region disappeared early in October.
The ozone hole this year now appears to have stabilized, the vortex remained quite symmetrical for several weeks, until early October when a familiar distortion towards the eastern Pacific occurred. This is the type of distortion that precedes the southern tip of South America coming under the hole. The vortex has remained distorted over the entire October 3-10 period. The ozone hole just passed over the southern tip of South America for the first time this season on October 10. A symmetrical ozone hole was evident during October 11- 13, becoming distorted in a similar way to early October during October 14-19. The ozone hole just passed over the southern tip of South America for the second time this season on October 19. Since October 19, the hole has become symmetrical again, but no longer lies centred on Antarctica, with a significant shift of the vortex towards S. Africa on October 24. The vortex has remained symmetrical until October 30, with another significant distortion developing towards S. Africa by November 1. By November 4 the vortex became symmetrical again, remaining so until November 9, when a significant distortion towards S. Africa occurred. The distortion remained until November 13 and then becoming more symmetrical again on November 14-17. The distortion towards Africa appeared again on November 18 and rotated to the longitude of Western Australia by November 22. The ozone hole became elongated from November 25 to December 7, gradually becoming more symmetrical again through to December 12. The ozone hole began to break up on December 14 as the main body of the ozone hole moved off the pole, likely for the last time this season. A massive break-up occurred on December 17 and the ozone hole remnant moved off the Antarctic continent on December 19, moving north of 60°S into the South Pacific (midway between NZ and S. America) on December 20, and dissipated completely by December 22.
The ozone maximum formed in the ridge immediately south of Australia by the third week of August, reached a maximum in excess of 450 DU around 21 August and persisted until 26 August, before dissipating. By the first week of September, the ozone ridge is weak and centred near MacquarieIsland. By September 7 a small but intense ridge developed just north of 60°S, mid-Pacific, disappearing by September 10. This is an unusually high-latitude ridge, not doubt its position is related to the orientation of the distorted vortex. By September 12-13 the ridge had re-appeared at more ‘traditional’ longitudes (south of Australia) but at a very high latitude (60°S). It would not be surprising for the MacquarieIsland ozone instrument to see near-record high ozone levels around 13 September. This ridge in the vicinity of MacquarieIsland further intensified in the third week of September, peaking at over 475 DU during 16-17 September before dissipating and moving eastwards. The ridge has intensified again on September 24-25, south of New Zealand. MacquarieIsland would have experienced high ozone levels (>450 DU) on September 24. By early October the ridge had dissipated, reforming with a strong, but localised maximum (>450 DU) on October 6, way south of Australia, almost at 60°S. This transient ridge quickly disappeared by October 10, reappeared briefly (October 14-16), before dissipating again on October 18. It has not reappeared since October 18. A high latitude, relatively weak ridge developed in the far south Pacific toward S. America on October 27-28, dissipating soon after. Since then and up to November 22 there has been no significant ozone ridge development in the Southern Hemisphere.
The Australian Antarctic Stations are often on the edge of the Antarctic ozone hole defined by the 220 DU contour. On September 5 an unusual event occurred, with Mawson and Davis being both inside the hole due to a vortex extension (distortion) around 70°E longitude (towards the Indian Ocean). On September 6-7, this distortion had moved to around 100°E longitude placing Mawson and Davis outside of the 220 DU, but with Casey on the edge/inside of 220 DU contour. All 3 stations remained outside the hole until 13 September when Mawson and Davis were again inside the 220 DU contour, with the above mentioned pattern set to repeat with the elongated vortex. When the vortex assumed a symmetrical shape by September 19, all 3 Australian Antarctic stations were under the hole, and have continued to remain under the hole until at least 1 October. The October 3 distortion of the vortex means that Casey is now not under the hole and has remained outside the hole until October 10. Mawson and Davis were under the hole until October 8. Mawson and Davis went back under the hole on October 16, staying under the hole for the period October 19 - 25. Casey has been on or near the edge of the vortex from October 18. Casey finally moved back under the hole on October 25 staying there until October 31. On November 1, with the vortex distortion, Casey moved back from under the hole. Mawson and Davis have been under the hole since October 16. Throughout November and December, the Australian Antarctic stations have been close to the edge, sometimes inside, sometimes outside, of the Antarctic ozone hole. The ozone hole passed very close to the southern tip of S. America on November 19-21.
EESC and Melbourne Ozone
Prof Ian Rae requested a revised version of the EESC/Melbourne column ozone plot that appeared in the DEWHA/BoM/CSIRO ozone calendar for the month of November 2010. The ozone data (QBO adjusted) have been updated by Dr M. Tully (BoM) to include 2009 ozone data, as have the EESC data, which are derived from observations at CapeGrim of 5 CFCs, 3 HCFCs, 5 chlorocarbons, 3 halons and methyl bromide, see Figure 5. The EESC data calculated here are higher than calculated previously, due to a higher CFC-11 chlorine release factor (0.84 compared to 0.80) for a typical air mass exchange between the troposphere and the stratosphere. The chlorine release factors for all other ODSs are scaled to the CFC-11 factor. The troposphere to stratosphere transport time used is 2.5 years.
There is clearly a significant correlation between Melbourne column ozone and EESC. This does not prove a cause-and-effect relationship but is consistent with it. The relationship between levels of effective chlorine in the stratosphere and the resultant ozone depletion has been established by direct measurements in the stratosphere during field campaigns and by detailed models of stratospheric transport and chemistry that incorporate all the important chemistry and transport processes to model halogen-induced stratospheric ozone loss.
Summary: WMO Antarctic Ozone Bulletin No 1/2010 (released 27 August)
Stratospheric temperature trends and the trends in temperature in regions where PSCs form both indicate a major stratospheric warming occurred from mid-July until early August. This has resulted in several factors leading to a small ozone hole at this stage: a reduced area of PSCs compared to the long term average (PSCs are required to form the ozone hole) and a perturbed vortex (perturbed vortices are warmer than average). This has resulted in a very low area ozone hole at this stage. The lower levels of PSCs and ClO observed over Antarctica this year suggest a relatively small hole in 2010.
The picture will become much clearer over the next few weeks – if the vortex remains disturbed then this year’s hole will indeed be significantly smaller than those of the past 5 years.
Summary: WMO Antarctic Ozone Bulletin No 2/2010 (released 17 September)
By the end of August, stratospheric temperatures reached their long-term means, but a new warming event is currently on the way, which may further weaken this hole and has caused a reduction in the levels of PSCs. The area of the ozone hole is low compared to recent years. The low levels of PSCs and reactive chlorine in the vortex points towards a small hole for 2010.
Summary: WMO Antarctic Ozone Bulletin No 3/2010 (released 8 November)
The heat flux between 450S and 750S is an indicator of how much the stratosphere (and the Antarctic vortex) is disturbed. Before mid-July, the stratosphere was largely undisturbed, but, between mid-July and early September, two stratospheric warming events resulted in significant increases in this heat flux, indicating disturbance. However, since early September, the stratosphere (and the Antarctic vortex) has been stable based on the heat-flux indicator.
The WMO Bulletin reports a maximum ozone mass deficit of about 23 Mt in late September compared to our calculated value of 26 Mt at the same time.
Recent Literature
Colleagues have alerted us to several recent papers on stratospheric ozone.