The 2017 Antarctic Ozone Hole Summary: Report #5, Tuesday26September2017
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 & 100hPa 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 thehole 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 hPalie 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 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.
Ozone deficit
The bottom panel of Figure 1 shows that by mid-August there were small levels of estimated daily ozone deficitcorresponding 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.
Ozone hole minima
The first excursions below 220 DU occurred in early August around the fringes of the polar night (see Figures 3 & 4), and since 4 August have remained below 220 DU, dropping to 176 DU on 10 August before recovering to 202 DU by 13 August.This metric can be highly variable at this time of year, but this variability is expected to reduce in the next two to three weeks as the polar night reduces and the ozone hole fully forms. During the second half of August and early September the ozone hole minima continued to show variability, dropping to 175 DU on 17 August before rising again to 202 DU on 22 August. By 2 September the ozone hole minima had dropped again to 184 DU with indications that the variability in this metric has reduced considerably.
The ozone minima dropped to 159 DU by 8 September, which is middle of the pack compared with the last 5 ozone holes for this time of year.Overall, the ozone minima increased during the second week of September to be between 166-170 DU by 15 September. Similar to the other metrics, this is now considerably higher when compared with the past 5 ozone holes and the 1979-2016 mean for this time of year. Overall, the third week of September saw the daily ozone minima remain in the range 155-170 DU, considerably higher than the 1979-2016 mean for this time of year.
Average ozone in the hole
The average ozone amount in the hole (averaged column ozone amount in the hole weighted by area; Figure 2 bottom panel) shows a similar pattern to that of the ozone hole minima. The average ozone amount dropped to 199 DU on 10 August, and by 13 August had risen to 214 DU.Following this, the average ozone amount fluctuated between 201 DU and 214 DU, and ended at 205 DU on 2 September.
After the first week of September, the average ozone amount in the hole had dropped to 199 DU, and similar to the ozone deficit, this is on the higher side for this time of year compared with the past 5 ozone holes. The average ozone amount in the hole dropped to 192 DU on 10 September before rising again to be at 198 DU by 15 September, which is now substantially higher when compared with the past 5 ozone holes and the 1979-2016 mean for this time of year. There was an overall small decrease in the average ozone amount in the hole during the third week of September, dropping to approximately 190 DU by 23 September. This remains substantially higher than the 1979-2016 mean for this time of year.
Total column ozone images
The most recent 16 days of total column ozone ‘images’ over Australia and Antarctica from OMI are shown in Figure 3 and from OMPS are shown in Figure 4.
From early August onwards, the ozone hole can be seen forming in several areas around the polar night. By the end of the second week of August the Antarctic polar night still covered most of Antarctica. The strong ridge of high ozone in the band immediately south of Australia between about 40-60S is present again in 2017.Figure 4 shows the ozone hole images from 18 August through to 2 September and what can be clearly seen is the ozone hole forming in earnest from 29 August onwards; it is expected that the 220 DU contour shown in red will be completely closed within the next week.
From 3-8 September the ozone hole can be seen to continue to form, with the 220 DU contour now almost completely enclosed. During this period, the 3 Australian Antarctic stations were outside of the ozone hole, and Macquarie Island remained under a ridge of high ozone. On 8 September, the tip of South America was just touching the edge of the ozone hole. From 1 – 10 September it can be seen that the polar vortex/ozone hole was relatively symmetrical with a ridge of high ozone around much of the 30-60S latitude band. 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. By 15 September, the elongation was along an axis of 90E – 90W with the tip of South America under the hole on 14-15 September. By 15 September, both Mawson and Davis stations were within the ozone hole. The distortion of the ozone hole continued from 16 to 23 September with the elongation propagating around the South Pole from west to east during this period, indicating continued strong wave activity. On 16 September, all 3 Australian Antarctic stations were inside the ozone hole.
NASA MERRA heat flux and temperature
The MERRA 45-day mean 45-75S heat fluxes at 50 & 100hPa 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 60-90S zonal mean temperatures at 50100hPa are shown in Figure 6, these usually show an anti-correlation to the heat flux.
At 50 hPa, the type 1 PSC (HNO3.3H2O) formation threshold temperature (195K) was reached in mid- to late June. At 100 hPa, the threshold temperature was reached in early July.
May, June, July
During mid-May to mid-Junethe45-75S heat flux at 50 & 100 hPa was higher than compared to the 1979-2016 range, indicating lessheat transported towards the pole. Correspondingly, the 60-90S zonal mean temperatures at 50 & 100hPa werelower than average being in the lower 10-30th percentile or lowest 10 percentile of the 1979-2016 range. From mid-June to end of July, the 45-75S heat flux at 50hPa& 100 hPa shifted down to be at the 30thpercentile mark of the 1979-2016 range, indicating more heat transport towards the pole. Interestingly, the 60-90S zonal mean temperatures at 50 & 100hPa from mid-June to the end of July essentially remained in the lowest 30 percentile range.
August
The first two weeks of August saw the 45-75S heat flux at 50 & 100 hParemain at approximately the 30thpercentile mark of the 1979-2016 range. The corresponding 60-90S zonal mean temperatures at 50 & 100hPa during the first two weeks of August increased to close to the 1979-2016 average, before increasing to be in the upper 70-90th percentile of the 1979-2016 range, indicating the beginning of a warming event. 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, both levels were in the lowest 10% of the 1979-2016 range, with the 50 hPa trace briefly dropping below the previous minimum value. Following this, the heat flux at both levels increased again to be in the 10-30% mark of the 1979-2016 range. Correspondingly, the 60-90S zonal mean temperatures at 50 & 100hPa during the last half of August increased to be in the highest 10% of the 1979-2016 range. By early September the temperatures at the both 50 & 100 hPa had dropped sharply to be back in the 70-90% mark of the 1979-2016 range. The forecast suggests that the temperatures at the both 50 & 100 hPa will remain relatively constant over the coming week.
September
The first week of September saw the 45-75S heat flux at 50 & 100 hPa remain in the 10-30% mark of the 1979-2016 range, while the60-90S zonal mean temperatures at the both 50 & 100 hPa remained in the 70-90% mark of the 1979-2016 range. The 45-75S heat flux 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. 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. The forecast is for this warming event to continue and increase over the next week. A corresponding large increase in the 60-90S zonal mean temperatures at the both 50 & 100 hPa was seen as a result, 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 temperatures at the both 50 & 100 hPa levels to track along the previous maximum temperature envelope, indicating a very warm low to mid-stratosphere for this time of year. The 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 hPalie 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 during this period. The forecast for the coming week is for the heat flux and temperatures to return to more ‘normal’ levels for this time of year.