The 2017 Antarctic Ozone Hole Summary: Report #9, Tuesday 24 October 2017
Paul Krummel and Paul Fraser
CSIRO Oceans and Atmosphere, Climate Science Centre
Aspendale, Victoria
Summary
For the 2017 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). Unless otherwise stated, the metrics quoted in this report are calculated from the OMPS data products. Please note the OMPS data used in this report are the Level 3 data created from Version 2 (V2) of the Nadir Mapper (NM) dataset from the Suomi National Polar-orbiting Partnership satellite.
August
The first excursions below 220 DU of the ozone minima occurred in early August around the fringes of the polar night, and since 4 August have remained below 220 DU, dropping to 176 DU on 10 August before recovering to 202 DU by 13 August. During the first two weeks of August the ozone hole area peaked at 3.9 million km2 on 8 August before reducing to 3.3 million km2 by 13 August. The forecasts from Merra2 of the 50 & 100 hPa temperatures and heat fluxes are indicating a significant warming event in the coming week, which may see the ozone levels rise above 220 DU again. The forecast warming event did occur, with the 45-75S heat flux at 50 & 100 hPa dipping to low values (more heat transported towards the hole) on 27-28 August, and the corresponding 60-90S zonal mean temperatures at 50 & 100 hPa increasing to be in the highest 10% of the 1979-2016 range through the second half of August. This resulted in the ozone hole area and deficit dropping sharply, while the ozone minima metrics increased, during the fourth week of August. However, by the end of August and early September, the ozone hole area increased rapidly to be at 12.5 million km2 by 2 September, while the ozone deficit increased to about 4 million tonnes, and the ozone minima dropped to 184 DU. From 29 August onwards, the ozone hole images clearly show that the hole is forming in earnest and it is expect that the 220 DU contour will be completely closed within the next week.
September
The first week of September saw the ozone hole continue to get larger, with the area reaching 18.2 million km2, the daily ozone deficit increasing to 8.3 million tonnes and the minima dropping to 159 DU by 8 September. The 45-75S heat flux and 60-90S zonal mean temperatures remained relatively stable during the first week of September, however, the forecast data are suggesting a sudden strong warming event over the coming week, which is reflected as an increase in the 60-90S zonal mean temperatures into the top 10th percentile of the 1979-2016 range. This will likely have a considerable impact on the ozone hole metrics over the next week. The predicted warming event did occur during the second week of September with the 45 day mean 45-75S heat flux at 50 & 100 hPa dropping well into the lowest 10 percentile band of the 1979-2016 range (indicating more heat transported towards the pole) and a corresponding large increase in the 60-90S zonal mean temperatures at the both 50 & 100 hPa, with the temperature at both levels lying on, or exceeding, the previously seen (1979-2016 timeframe) maximum temperatures for this time of year. The forecast for the coming week is for the warming event to continue, with temperatures at the both 50 & 100 hPa levels predicted to track along the previous maximum temperature envelope, indicating a very warm low to mid-stratosphere for this time of year. The result of this warming has been a reduction in the size and depth of the ozone hole over during the second week of September; the ozone hole area peaked at 19.1 million km2 on 11 September, before dropping back to be at 17.7 million km2 by 15 September and the ozone minima increased to be between 166-170 DU by 15 September. From 11 September onwards the ozone hole has become quite elongated and displaced off of the South Pole with the ridge of high ozone now over parts of the Antarctic mainland, indicating some strong wave activity. The tip of South America was inside the hole on 14-15 September, and both Mawson and Davis stations were within the ozone hole on 15 September.
The stratospheric warming event continued during the third week of September, with the 45 day mean 45-75S heat flux at 50 & 100 hPa tracking along the previously seen (1979-2016 timeframe) minimum until 22 September, indicating strong transport of heat towards the South Pole. The result of this saw the 60-90S zonal mean temperatures at the both 50 & 100 hPa lie on, or exceed, the previously seen (1979-2016 timeframe) maximum temperatures for the period of about 14-21 September. This supports the apparent strong wave activity noted in the daily images which manifested itself as a large distortion of the ozone hole from 14 to 23 September with the elongation propagating around the South Pole from west to east. The forecast for the coming week is for the heat flux and temperatures to return to more ‘normal’ levels for this time of year. The warming event has had a large impact on the ozone hole metrics with 1) the daily ozone hole area continuing to decrease during the third week of September, dropping to 15.3 million km2 by 23 September which is well below the 1979-2016 mean for this time of year; 2) the daily ozone deficit remaining relatively constant (with some fluctuation) around 10 million tonnes, which is about half of the 1979-2016 mean for this time of year; and 3) the daily ozone minima remaining in the range 155-170 DU, considerably higher than the 1979-2016 mean for this time of year. If the ozone hole does not increase substantially over the next few weeks, then the 2017 ozone hole is likely to be one of the smallest ozone holes, similar in size to what was observed in the mid- to late-1980s. The warming event came to an end during the third week of September with stratospheric conditions returning to more normal levels. The 45 day mean 45-75S heat flux at 50 & 100 hPa returned to the 10-30 percentile band of the 1979-2016 range, with the forecast for the coming week indicating that the heat flux at these two levels will end up at about the long-term mean of the 1979-2016 range. This is indicating far less heat transported towards the pole and partly explains the growth in the ozone hole metrics during the last week of September, which saw a sharp increase in the ozone hole area reaching 18.5 million km2 by 30 September; the daily ozone deficit rose sharply to be at 16.8 million tonnes by 30 September; and the daily ozone minima dropped rapidly to be at 137 DU by 30 September. During 25-30 September, the ozone hole became much more symmetrical and stable indicating less stratospheric wave activity during this period.
October
The first week of October saw the Antarctic ozone hole remain relatively stable and symmetrical in shape, with the Australian Antarctic bases of Mawson and Davis within or on the edge of the ozone hole from 2-6 October. The ozone hole metrics indicated that the ozone hole reduced in size and depth during the first week of October, with the ozone hole area reducing to 16.6 million km2 by 6 October; the daily ozone deficit dropping to 15.3 million tonnes by 6 October; and the daily ozone minima dropping to 132 DU on 1 & 2 October before rising to 143 DU by 6 October. The ozone hole remained relatively symmetrical and stable from 7-11 October, before becoming elongated again along an axis of 90E – 90W by 13 October. This saw the ozone hole metrics peak (dip) again on 11 October before reducing (increasing) again. On 11 October the daily ozone hole area reached another peak at 18.3 million km2 and the daily ozone deficit peak at 18.5 million tonnes (highest so far this season). On 9 & 12 October the ozone hole minima dropped to 131 DU, the lowest value so far this year. For the period 7-13 October, the Australian Antarctic bases of Mawson and Davis were inside the ozone hole, while Casey station was on the edge of the ozone hole on 8-9 October. The ozone hole remained elongated from 13 to 17 October, briefly appeared to be more stable on 18-19 October, before becoming distorted again. By 21 October, the ozone hole was displaced off of the South Pole towards South America by a ridge of high ozone immediately south of Australia. For the period 15-21 October, all three Australian Antarctic bases were outside of the ozone hole, and on 19-21 Oct they were under the ridge of high ozone. The resultant changes in the ozone hole metrics were that the daily ozone hole area dropped to 14 million km2 by 21 October; the daily ozone deficit dropped to 10.2 million tonnes by 21 October; and the daily ozone hole minima jumped up to 157 DU by 21 October. We can now provide some provisional rankings for the 2017 Antarctic ozone hole. Of the 38 holes for which we have data since 1979, the 2017 hole is provisionally ranked:
29th: 15-day average area 28th: 15-day average minimum ozone
29th: daily maximum area 28th: daily minimum ozone
28th: daily ozone deficit 28th: daily min average ozone amount in the hole
So, overall, the 2017 Antarctic ozone hole is one of the smallest ozone holes since the mid-1980s, smaller than the 2012 ozone hole, and comparable to the 2002 ozone hole which split in two.
The 2017 ozone hole
Ozone hole area
The top panel of Figure 1 shows that during the first two weeks of August the ozone hole area peaked at 3.9 million km2 on 8 August before reducing to 3.3 million km2 by 13 August. The second half of August through to early September saw the ozone hole area initially peak at 6.1 million km2 on 15 August, then drop back to 1.7 million km2 on 22 August before increasing rapidly to be at about 12.5 million km2 by 2 September. This is similar in size to the 2012, 2014 & 2015 ozone holes for the same time of year. From 26 August onwards there is a noticeable difference between the ozone hole area calculated from OMPS and OMI – on average the ozone hole area calculated from OMI is about 30% lower than the OMPS equivalent. This difference is expected to decrease once the ozone hole fully closed and the polar night reduced.
The first week of September saw the ozone hole area continue to increase, reaching 18.2 million km2 by 8 September. During the second week of September, the ozone hole area peaked at 19.1 million km2 on 11 September, before dropping back to be at 17.7 million km2 by 15 September. Compared to the ozone holes from the last 5 years, this years’ hole is on the lower side in terms of areal extent and is similar in size to the 1979-2016 mean for this time of year. The daily ozone hole area continued to decrease during the third week of September, dropping to 15.3 million km2 by 23 September. This is now well below the 1979-2016 mean for this time of year. Following this reduction in the daily ozone hole area, the fourth week of September saw a sharp increase again in this metric reaching 18.5 million km2 by 30 September, which is similar to the long-term 1979-2016 mean for this time of year.
Following the second peak in the daily ozone hole area on 30 September, the first week of October saw the ozone hole area decrease again to be 16.6 million km2 by 6 October. The second week of October saw another peak in the daily ozone hole area with it reaching 18.3 million km2 on 11 October before decreasing again to 16.5 million km2 by 13 October. During the third week of October the daily ozone hole area continued to decrease, dropping to 14 million km2 by 21 October.
Ozone deficit
The bottom panel of Figure 1 shows that by mid-August there were small levels of estimated daily ozone deficit corresponding to the above mentioned ozone hole areas. The estimated daily ozone deficit reached 1.3 million tonnes on 10 August before dropping back to < 0.5 million tonnes on 13 August. Similar to the ozone hole area, the second half of August through to early September saw the estimated daily ozone deficit peak at 2.4 million tonnes on 15 August, then drop back to 0.3 million tonnes on 22 August before increasing to be at about 4 million tonnes by 2 September.
During the first week of September, the daily ozone deficit increased to 8.3 million tonnes by 8 September, which is on the lower side for this time of year compared with the past 5 ozone holes. The second week of September saw the daily ozone deficit peak at 11.2 million tonnes on 11 September before falling to 8.4 million tonnes by 15 September. This is now considerably lower than the past 5 ozone holes and the 1979-2016 mean for this time of year. During the third week of September the ozone deficit remained relatively constant (with some fluctuation) around 10 million tonnes, which is about half of the 1979-2016 mean for this time of year. During the fourth week of September the daily ozone deficit rose sharply to be at 16.8 million tonnes by 30 September. This is still well below the 1979-2016 mean for this time of year.
During the first week of October the daily ozone deficit started to decrease again, ending at 15.3 million tonnes on 6 October, which suggests that the value of 16.8 million tonnes recorded on 30 September may be the peak value for 2017. The second week of October saw the daily ozone deficit peak at 18.5 million tonnes on 11 October (surpassing the 30 September peak) before dropping sharply to be at 14 million tonnes by 13 October. For pretty much the whole ozone hole season so far, the 2017 daily ozone deficit has been well below the long-term 1979-2016 mean for this metric. The daily ozone deficit continued to drop during the third week of October, down to 10.2 million tonnes by 21 October.