Antarctic Ozone Bulletin

Transcription

1 Antarctic Ozone Bulletin No 2 / 2008 View of the Argentinian station Belgrano at 79 S. The Brewer spectrophotometer can be seen on the observation platform in the middle of the photo. Data from this station can be found on page 13. G l o b a l A t m o s p h e r e Wa t c h 24 Sep. 2008

2 Executive Summary On most days from late June until early August the minimum temperatures at 50 hpa were below those of 2006 and Since the last Bulletin the minimum temperature has varied between the average and the minimum. On two occasions, 30 August and 4 September, it was colder than for any year in the time period on those dates. 50 hpa temperatures averaged over the S region have been below the average on most days since early June with the exception of a warm period of a few days in early August. From 29 August to 1 September it was lower than any year in the time period for these dates. A similar development is also seen at the 70 hpa level. At 30 hpa the S region has been considerably colder than the average since mid June. At 10 hpa the S region has been colder than the long-term mean the whole winter and on most days since mid June it has been below the extreme low. Since late June, temperatures low enough for nitric acid trihydrate (NAT or PSC type I) formation have covered an area of more than 20 million square kilometres, or about 80% of the vortex area. Since the onset of NAT temperatures in mid-may the NAT area was close to the average until late June. From early July until now the NAT area has been above the average on most days and also above that of 2007, but below that of In mid September the NAT area has been close to the extreme maximum of the period for that time of the year. The vortex has been more concentric around the pole in 2008 than in This led to an onset of ozone depletion that was close to the average during the early stages of ozone depletion in early August. After than the ozone depletion has increased rapidly and the ozone hole area passed the maximum of 2007 on 9 September. The longitudinally averaged heat flux between 45 S and 75 S is an indication of how much the stratosphere is disturbed. From April to the middle of July 2008, the heat flux was oscillating around the average. In mid-july, the heat flux decreased somewhat and has, since then, been below the average. This is a sign of a stable vortex. At the altitude of ~18 km the vortex is still almost entirely depleted of HCl, one of the reservoir gases that can be transformed to active chlorine. Most of the vortex is filled with ppb of active chlorine (ClO), and in some areas the ozone mixing ratio has dropped from around 3 ppm in early August to around 0.5 ppm in mid September. The south polar vortex is more concentric in 2008 than in 2007, and this has led to a relatively late onset of ozone depletion. The area of the region where total ozone is less than 220 DU is denoted as the ozone hole area. During the first half of August, the area increased more slowly than at the

3 same time in After mid August the ozone hole areas has increased rapidly and reached a maximum of 27 million square kilometres on 12 September. After 17 September, the ozone hole areas has started to decline and as of 22 September it is approx. 25 million square kilometres. In comparison, the maximum area reached in 2007 was around 25 million square kilometres and in 2006 it was above 29 million square kilometres. WMO and the scientific community will use ozone observations from the ground, from balloons and from satellites together with meteorological data to keep a close eye on the development during the coming weeks and months.

4 Introduction The meteorological conditions in the Antarctic stratosphere found during the austral winter (June-August) set the stage for the annually recurring ozone hole. Low temperatures lead to the formation of clouds in the stratosphere, so-called polar stratospheric clouds (PSCs). The amount of water vapour in the stratosphere is very low, only 5 out of one million air molecules are water molecules. This means that under normal conditions there are no clouds in the stratosphere. However, when the temperature drops below -78 C, clouds that consist of a mixture of water and nitric acid start to form. These clouds are called PSCs of type I. On the surface of particles in the cloud, chemical reactions occur that transform passive and innocuous halogen compounds (e.g. HCl and HBr) into so-called active chlorine and bromine species (e.g. ClO and BrO). These active forms of chlorine and bromine cause rapid ozone loss in sun-lit conditions through catalytic cycles where one molecule of ClO can destroy thousands of ozone molecules before it is passivated through the reaction with nitrogen dioxide (NO 2 ). When temperatures drop below -85 C, clouds that consist of pure water ice will form. These ice clouds are called PSCs of type II. Particles in both cloud types can grow so large that they no longer float in the air but fall out of the stratosphere. In doing so they bring nitric acid with them. Nitric acid is a reservoir that liberates NO 2 under sunlit conditions. If NO 2 is physically removed from the stratosphere (a process called denitrification), active chlorine and bromine can destroy many more ozone molecules before they are passivated. The formation of ice clouds will lead to more severe ozone loss than that caused by PSC type I alone since halogen species are more effectively activated on the surfaces of the larger ice particles. The Antarctic polar vortex is a large low-pressure system where high velocity winds (polar jet) in the stratosphere circle the Antarctic continent. Figure 1 depicts the vortex on 16 September for the three years of 2006, 2007 and The region poleward of the polar jet includes the lowest temperatures and the largest ozone losses that occur anywhere in the world. During early August, information on meteorological parameters and measurements from ground stations, balloon sondes and satellites of ozone and other constituents can provide some insight into the development of the polar vortex and hence the ozone hole later in the season. The situation with annually recurring Antarctic ozone holes is expected to continue as long as the stratosphere contains an excess of ozone depleting substances. As stated in the Executive Summary of the 2006 edition of the WMO/UNEP Scientific Assessment of Ozone Depletion, severe Antarctic ozone holes are expected to form during the next couple of decades. For more information on the Antarctic ozone hole and ozone loss in general the reader is referred to the WMO ozone web page: ozone/index.html.

5 Figure 1. Polar orthographic map of potential vorticity at the potential temperature level of 500 K (ca. 20 km) over the south polar region on 16 September 2006, 2007 and It can be seen that the vortex extended further north in 2007 than in 2006 and The plot is based on data from the European Centre for Medium range Weather Forecasts (ECMWF). Data extraction and plotting is done at the Norwegian Institute for Air Research (NILU). 16 Sep UT PV (10-6 Km2/kgs) 16 Sep UT 16 Sep UT

6 Meteorological conditions Temperatures Meteorological data from the National Center for Environmental Prediction (NCEP) in Maryland, USA, show that stratospheric temperatures over Antarctica have been below the PSC type I threshold of -78 C since early May and below the PSC type II threshold of - 85 C since early June, as shown in Figure 2. This figure also shows that the daily minimum temperatures at the 50 hpa level have been close to or below the average. On most days from late June until early August the minimum temperatures at 50 hpa were below those of 2006 and Since the last Bulletin the minimum temperature has varied between the average and the minimum. On two occasions, 30 August and 4 September, it was colder than for any year in the time period on those dates. Data from NCEP, made available through the Ozonewatch web page of NASA (see section on Acknowledgements and links at the end of the Bulletin), show that the 50 hpa temperatures averaged over the S region (Figure 3, next page) have been below the average on most days since early June with the exception of a warm period of a few days in early August. From 29 August to 1 September it was lower than any year in the Temperature [K] HNO 3 = 6 ppbv, H 2 O = 4 ppmv S Minimum Temperature 50 hpa % 30-70% Type I PSC Type II PSC Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 2. Time series of daily minimum temperatures at the 50 hpa isobaric level south of 50 S. The red curve shows 2008 (until 14 September). The somewhat darker red colour shows the development since the figure shown in the last bulletin (20 August). The blue line shows 2007 and the green line The average of the period is shown for comparison in black. The thin black lines represent the highest and lowest daily minimum temperatures in the time period. The light blue-green shaded area represents the 10th and 90th percentile values and the dark bluegreen shaded area the 30th and 70th percentiles. The two horizontal green lines at 195 and 188 K show the thresholds for formation of PSCs of type I and type II, respectively. The plot is adapted from a plot downloaded from the Ozonewatch web site at NASA and based on data from NOAA/NCEP.

7 Meteorological conditions time period for these dates. A similar development is also seen at the 70 hpa level. At 30 hpa the S region has been considerably colder than the average since mid June. At 10 hpa the S region has been colder than the long-term mean the whole winter and on most days since mid June it has been below the extreme low. As of 15 September it is still below the extreme low. The mean temperature at 70, 50, 30 and 10 hpa in the S region has behaved quite similarly to the temperature averaged over the S region. PSC Area and volume Since late June, temperatures low enough for nitric acid trihydrate (NAT or PSC type I) formation have covered an area of more than 20 million square kilometres, or about 80% of the vortex area. Since the onset of NAT temperatures in mid-may the NAT area was close to the average until late June. From early July until now the NAT area has been above the average on most days and also above that of 2007, but below that of The last K S Zonal Mean Temperature at 50 hpa % 30-70% Type I PSC Type II PSC HNO 3 = 6 ppbv, H 2 O = 4 ppmv Figure 3. Time series of temperature averaged over the region south of 60 S at the 50 hpa level. The red curve shows 2008 (until 14 September). The blue and green curves represent 2007 and 2006, respectively. The average of the period is shown for comparison in black. The two thin black lines show the maximum and minimum average temperature for during the time period for each date. The light blue-green shaded area represents the 10th and 90th percentile values and the dark blue-green shaded area the 30th and 70th percentiles. The plot is adapted from a plot downloaded from the Ozonewatch web site at NASA and based on data from NOAA/NCEP. 180 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

8 Meteorological conditions million km 2 Volume [10 6 km 3 ] Southern Hemisphere PSC NAT Area at Θ = 460 K A Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec B % 30-70% Southern Hemisphere PSC NAT Volume % 30-70% Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec days (mid September) the NAT area has been close to the extreme maximum of the period for that time of the year. The development of the NAT area is shown in Figure 4A. Rather than looking at the NAT area at one discrete level of the atmosphere it makes more sense to look at the volume of air with temperatures low enough for NAT formation. The so-called NAT volume is derived by integrating the NAT areas over a range of levels. The daily progression of the NAT volume in 2008 is shown in Figure 4B in comparison to recent winters and long-term statistics. Since the onset of PSCs in early May, Figure 4. Time series of the surface area at 460 K (panel A) and the volume (panel B) of the region where temperatures are low enough for the formation of nitric acid trihydrate (NAT or PSCs of type I). The red curve shows 2008 (until 14 September). The somewhat darker red colour shows the development since the figure shown in the last bulletin (20 August) The blue and green curves represent 2007 and 2006, respectively. The average of the period is shown for comparison in black. The two thin black lines show the maximum and minimum values during the time period for each date. The light blue-green shaded area represents the 10th and 90th percentile values and the dark blue-green shaded area the 30th and 70th percentiles. The plot is adapted from plots downloaded from the Ozonewatch web site at NASA and based on data from NOAA/NCEP.

9 Meteorological conditions the NAT volume has been above the average every day. Since mid June it has been considerably higher than the long-term mean and on several days similar to or even above the values of On a couple of occasions the 2008 values surpass the maximum for the period. The NAT volume has passed the maximum and is now decreasing in the same way as earlier years. The last few days it has been close to the maximum for the period. The area or volume with temperatures low enough for the existence of PSCs is directly linked to the amount of ozone loss that will occur later in the season, but the degree of ozone loss depends also on other factors, such as the amount of water vapour and HNO 3. Based upon the historical meteorological record it is expected that the extent and frequency of PSC occurrence will continue to decrease now as the sun rises over Antarctica, whereas the vortex area will level off and start to decline slowly. Vortex size and stability Figure 1 shows maps of potential vorticity on 16 September for 2006, 2007 and 2008 at the 500 K potential temperature level (~ 20 km). This map indicates how isolated the polar air mass is from air masses outside the polar vortex. Yellow, orange and red colours depict regions where the air is particularly well isolated from the surroundings. The vortex has been more concentric around the pole in 2008 than in This led to an onset of ozone depletion that was close to the average during the early stages of ozone depletion in early August. After than the ozone depletion has increased rapidly and the ozone hole area passed the maximum of 2007 on 9 September. The geographical extent of the south polar vortex has been higher than the average on almost every day since early April at the isentropic level of 460 K. At the 500, 550 and 600 K levels the vortex was larger than the average on most days until early August, but it has been smaller than average after that. It should be pointed out, however, that vortex size gives no direct indication of the degree of ozone loss that might occur later in the season. The longitudinally averaged heat flux between 45 S and 75 S is an indication of how much the stratosphere is disturbed. From April to the middle of July 2008, the heat flux was oscillating around the average. In mid-july, the heat flux decreased somewhat and has, since then, been below the average. This is a sign of a stable vortex. An updated plot of the heat flux can be found here: vt1-3w45_75-45s_100_2008.pdf

10 Ozone observations Satellite observations Since the last Bulletin, ozone depletion has progressed further. Figure 5 shows minimum ozone columns as measured by the SCIAMACHY instrument on board ENVISAT in comparison with data for the nine previous years (SCIAMACHY and GOME). Minimum ozone dropped rapidly from about 200 DU on 25 August to about 150 DU on 4 September. After that, the minimum values increased to 170 DU, but then started to decrease again and went down to approx. 130 DU on 24 September. During the next five days the minimum column is expected to vary between 130 and 135 DU. Dobson Units Minimum Ozone Column in the Southern Hemisphere GOME / SCIAMACHY Assimilated Ozone KNMI / ESA 24 Sep Aug 01 Sep 01 Oct 01 Nov 01 Dec fc 31 Dec Figure 5. Daily minimum total ozone columns in the Southern Hemisphere as observed by GOME, and S C I A M A C H Y. The black dots show the SCIA- MACHY observations for The data now show minimum ozone columns down to DU. The open circles are forecast data. The plot is provided by the Netherlands Meteorological Institute (KNMI). 10

11 Ozone observations Figure 6 shows minimum ozone as measured with the OMI instrument on board the AURA satellite. According to these measurements, minimum ozone reached 127 DU on 21 September, down from about 180 DU on 23 August. Figure 7 (next page) shows satellite maps from OMI for 18 September for the years 2006, 2007 and It can be seen that the extent of ozone depletion in 2008 is smaller than in 2008 but larger than in Total ozone [DU] Southern Hemisphere Minimum Ozone from OMI % 30-70% Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 6. Daily minimum total ozone columns in the Southern H e m i s p h e r e as observed by OMI and TOMS. The red curve show the OMI observations for 2008 until 21 September. The darker red curve shows the development after the last bulletin (23 August). The plot is adapted from a plot d o w n l o a d e d from NASA s ozone watch web site. 11

12 Ozone observations 18 September September September 2008 Figure 7. Total ozone map for 18 September 2006, 2007 and 2008 based on data from OMI on board the AURA satellite. The data are processed and mapped at KNMI. 12

13 Ozone observations Balloon observations Belgrano Ozonesonde observations at Belgrano started in the end of July. Since then, total ozone, measured by integrating the ozonesonde profiles, has dropped rapidly from 242 DU on 23 July to 118 DU on 17 September. This is shown in Figure 8. Figure 9 shows three ozone profiles measured on 23 July, 10 September and 20 September, respectively. One can see the progression of ozone loss in the km Integrated ozone [DU] Total ozone from integrated ozonesonde profiles Belgrano Jul Aug Sep Oct Nov Dec Figure 8. Total ozone at the Argentine GAW station Belgrano (77.9 S, 34.6 W) as derived by integrating the ozonesonde profiles and adding residual ozone assuming constant mixing ratio of ozone from the balloon burst altitude to the top of the atmosphere. The total ozone values are taken from provisional data files. As the data might be recalculated, these values might change. The data should therefore be considered as preliminary. altitude region. After the fire on the icebreaker Irizar in April 2007 the delivery of supplies to Belgrano is suffering. The crew are now waiting for supplies from the sky or from other vessels, which might hardly get there before February and then only in favourable sea conditions. In any case they continue to operate the Brewer and to launch ozonesondes under these difficult circumstances. The photo on the cover shows the Belgrano station and its Brewer spectrophotometer. Altitude [km] Belgrano 23 Jul 2008: 244 DU 10 Sep 2008: 158 DU 20 Sep 2008: 127 DU Ozone partial pressure [mpa] Figure 9. Ozonesonde profiles measured at the Argentine GAW station Belgrano (77.9 S, 34.6 W) on 23 July (green), 10 September (blue) and 20 September

14 Ozone observations Marambio A time series of total ozone calculated from ozone soundings performed at the Argentine station Marambio since early June is shown in Figure 10. As can be seen from the figure, there is a lot of variability from one sounding to the next. Three individual ozone profiles are plotted in Figure 11. The two September profiles display clear signs of ozone destruction in the km altitude range and although the total ozone column is some Dobson Units higher on 21 September, one can see that the ozone depletion has progressed further. Altitude [km] Marambio Integrated ozone [DU] Total ozone from integrated ozonesonde profiles Marambio Jun Jul Aug Sep Oct Nov Dec Figure 10. Total ozone at the Argentine GAW station Marambio (64.2 S, 56.6 W) as derived by integrating ozonesonde profiles from early June until 20 September. The total ozone values are taken from provisional data files. As the data might be recalculated, these values might change. The data should therefore be considered as preliminary Jul 2008: 267 DU 10 Sep 2008: 161 DU 21 Sep 2008: 168 DU Ozone partial pressure [mpa] Figure 11. Ozone profiles observed at the Argentine GAW station Marambio (64.2 S, 56.6 W) on 12 July (green), 10 September (blue) and 21 September (red). Total ozone is calculated by integrating the sonde profile from the ground to the altitude of burst and then adding the residual by assuming a constant mixing ratio from that point to the top of the atmosphere. The data should be considered as preliminary. 14

15 Ozone observations Neumayer Total ozone columns deduced from soundings carried out at the German NDACC/GAW station at Neumayer (70.65 S, 8.26 W) show a rapid drop starting in late August. This is shown in Figure 12, which includes data up to 22 September. In 2007, total ozone over Neumayer declined during September, but this year it has levelled off at around 160 DU, whereas it was around 120 DU around 20 September Data received just prior to the distribution of the Bulletin shows that total ozone dropped to 116 DU on 24 September. 350 Total ozone from integrated ozonesonde profiles South Pole Figure 13 shows the km partial column derived from ozonesonde observations carried out at the NDACC/GAW station on the South Pole. Since the previous bulletin the partial column has dropped rapidly and on 18 September it was around 40 DU. Although ozone depletion set in relatively late, it is now similar to the previous years shown for comparison in Figure 13. South Pole km partial ozone column 300 Integrated ozone [DU] Neumayer May Jun Jul Aug Sep Oct Nov Dec Figure 12. Total ozone at the German NDACC/GAW station Neumayer (70.65 S, 8.26 W) as derived by integrating ozonesonde profiles from early May until 22 September. The total ozone values are taken from the provided data files. As the data might be recalculated, these values might change. The data should therefore be considered as preliminary. Figure 13. Partial column of ozone in the km height range for the NDACC/GAW station at the South Pole. The brown diamonds represent 2008 (until 18 September). A selection of previous winters are shown for comparison. The km range has been chosen since this is the altitude range where ozone depletion is the most severe. 15

16 Ozone observations Ground-based observations Dôme Concordia Total ozone is measured with a SAOZ spectrometer at the French/Italian NDACC GAW station at Dôme Concordia at 3250 masl on the Antarctic ice cap. The measurements from the beginning of May until 22 September are shown in Figure 14. Due to polar night, there were no measurements between 24 May and 19 July. Since the last bulletin the ozone column has dropped from about 300 DU to below 150 DU. Dôme Concordia is usually inside the polar vortex and hence the ozone column shows less variability than observed at Dumont d Urville, which is 1100 km further north. Dumont d Urville Dumont d Urville is located at the polar circle, which allows for SAOZ measurements around the year. Figure 15 shows the total ozone time series from 1 May until 22 September. While total ozone was around DU in May and June, it decreased to around DU in late August. After that it has varied between 190 and 340 DU. Dumont d Urville is located further north than Dôme Concordia and exposed to more sunshine, hence ozone depletion sets in 400 Dôme Concordia 400 Total ozone from SAOZ spectrometer Total ozone [DU] Total ozone [DU] Total ozone from SAOZ spectrometer May Jun Jul Aug Sep Oct Nov Dec Figure 14. Total ozone at the French/Italian NDACC/GAW station Dôme Concordia (75.1 S, E, 3250 masl) as measured by a SAOZ spectrometer. The data should be considered as preliminary Dumont d Urville May Jun Jul Aug Sep Oct Nov Dec Figure 15. Total ozone at the French NDACC/GAW station Dumont d Urville (66.7 S, E) as measured by a SAOZ spectrometer. The data are updated as of 22 September and should be considered as preliminary. 16

17 Ozone observations at an earlier date. On the other hand it is also very often at the edge of or even outside the vortex. The daily ozone values are calculated as the mean of measurements taken at sunrise and sunset. If the station is on the edge of the vortex, the instrument might take one measurement into the vortex and one out of vortex. The difference between a sunrise measurement and a sunset measurement can be more than 100 DU. San Martin The San Martin station (68.1 S, 67.1 W) is only 76 km from the Rothera station. Between 1 and 22 September, total ozone has varied between 254 DU (5 Sep) and 153 DU (9 Sep). On some days the measurements at San Martin and Rothera are very close (within 10 DU), whereas on others the difference is from DU. Halley The Halley station (75.6 S, 26.6 W) is operated by the British Antarctic Survey. Measurements started on 27 August after the polar night. The station has been inside the polar vortex on every day since the measurements started. The total ozone column has varied between 136 and 211 DU between 27 August and 18 September. It reached 136 DU on 4 September and 18 September. Rothera At the British NDACC/GAW station Rothera total ozone is measured with a SAOZ spectrometer. Since the station is close to the polar circle, observations can be carried out around the year. After the last Bulletin, the station has been both inside and outside the vortex, and total ozone has varied between 150 and 300 DU. The ozone time series is shown in Figure 16 with data up to 12 September. The most recent measurements show total ozone around 150 DU. Total ozone [DU] Total ozone from SAOZ spectrometer Rothera May Jun Jul Aug Sep Oct Nov Dec Figure 16. Total ozone at the British NDACC/GAW station Rothera (67.6 S, 68.1 W) as measured by a SAOZ spectrometer until 12 September. The data should be considered as preliminary. 17

18 Ozone observations Syowa Total ozone is measured at the Japanese GAW station Syowa with a Dobson spectrophotometer. These measurements have been carried out since Total ozone was near 300 DU at the beginning of August and decreased to around DU at the time of the last Bulletin. After that ozone has decreased further. With the exception of 2 September total ozone has been below 220 DU since 29 August. The lowest value measured so far in 2008 was on 21 September with 146 DU. is measured with a Dobson spectrophotometer. Low total ozone was observed during the first few days of August, with 199 DU on 2 August. By 10 August the ozone column reached almost 300 DU before coming down to around 240 DU on 20 August. Since the last Bulletin total ozone has varied between 190 and 290 DU, with values around 200 DU in mid September. This is in contrast to Rothera where ozone at this time is around 150 DU, despite the fact that the stations are only 300 km apart. Vernadsky Vernadsky station (65.3 S, 64.3 W) is run by the National Antarctic Scientific Centre of Ukraine. Total ozone 18

19 Chemical activation of the vortex Satellite observations Most of the south polar vortex is still depleted in HCl and filled with active chlorine. Figure 17 shows the extent of removal of hydrochloric acid (HCl), which is one of the reservoirs for active chlorine, for 17 September As can be seen from the figure, HCl is almost completely removed inside the vortex at the 490 K isentropic level. Compared to one month earlier the HCl depletion is now less complete, especially in the Pacific sector. Removal of HCl is an indicator for chemical activation of the vortex. Another indicator for vortex activation is the amount of chlorine monoxide (ClO). It should be noted, however, that ClO dimerises and forms (ClO) 2 in darkness. The dimer is easily cracked in the presence of sunlight. ClO will therefore be present in the sunlit parts of the vortex, whereas the dark areas will be filled with (ClO) 2, which is not observed by Aura-MLS. Figure 18 (next page) shows the amount of ClO on 17 September The sector from 0-90 E has particularly high ClO, with certain areas exceeding 1.65 ppb. This is more than one month earlier. Figure 19 (next page) shows the ozone mixing ratio at the 490 K isentropic level on 17 September. Since the last Bulletin, which showed the situation on 17 August, the ozone mixing ratio has decreased from nearly 3 ppm to around ppm in certain regions, especially over the western half of Antarctica. HCl 17 Sep 2008 ppbv Figure 17. Mixing ratio of HCl on 17 September 2008 at the isentropic level of 490 K (~18 km). The white contours indicate isolines of scaled potential vorticity. The map is made at NASA's Jet Propulsion Laboratory and based on data from the Aura-MLS satellite instrument. 19

20 Chemical activation of the vortex ClO 17 Sep Sep 2008 O 3 black SZA=94 o ppbv ppmv Figure 18. Mixing ratio of ClO on 17 September 2008 at the isentropic level of 490 K (~18 km). The white contours indicate isolines of scaled potential vorticity. The black contour line encircles the region where the solar zenith angle (SZA) is larger than 94º. The map is made at NASA's Jet Propulsion Laboratory and based on data from the Aura-MLS satellite instrument Figure 19. Mixing ratio of ozone on 17 September 2008 at the isentropic level of 490 K (~18 km). The white contours indicate isolines of scaled potential vorticity. The map is made at NASA's Jet Propulsion Laboratory and based on data from the Aura-MLS satellite instrument. 20

21 Ozone hole area and mass deficit The area of the region where total ozone is less than 220 DU (ozone hole area) as deduced from the OMI instrument on AURA is shown in Figure 18. During the first half of August, the area increased more slowly than at the same time in After mid August the ozone hole areas has increased rapidly and reached a maximum of 27 million square kilometres on 12 September. After 17 September, the ozone Area [10 6 km 2 ] Ozone Hole Area from TOMS/OMI % 30-70% Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Figure 18. Area (millions of km 2 ) where the total ozone column is less than 220 Dobson units is showed in red (until 22 September). The development since the last Bulletin is shown with a deeper red colour is shown in blue and 2006 in green. The smooth black line is the average. The dark green-blue shaded area represents the 30th to 70th percentiles and the light green-blue shaded area represents the 10th and 90th percentiles for the time period The plot is adapted from a plot downloaded from the NASA Ozonewatch web site and is based on data from the OMI instrument on AURA and various TOMS instruments. 21

22 Ozone hole area and mass deficit megaton Ozone Loss w.r.t. 220 DU in the Southern Hemisphere GOME / SCIAMACHY Assimilated Ozone KNMI / ESA 24 Sep forecast 0 01 Aug 01 Sep 01 Oct 01 Nov 01 Dec 31 Dec Figure 19. Ozone mass deficit (megatonnes) for the years from 1999 to 2008 (black dots). The mass deficit is the amount of ozone that would have to be added to the ozone hole in order to bring the total column up to 220 DU in those regions where the total column is below this threshold. The open circles represent a forecast for the next five days. This plot is produced by KNMI and is based on data from the GOME and SCIAMACHY satellite instruments. 22

23 Ozone hole area and mass deficit hole areas has started to decline and as of 22 September it is approx. 25 million square kilometres. Figure 19 (previous page) shows the ozone mass deficit as deduced from the GOME and SCIAMACHY satellite instruments. During August and the first half of September the ozone mass deficit was lagging behind all earlier years shown here, except 2002 and In mid September it passed the values of 2007 and on 22 September it reached 27 megatonnes, which is nearly the same as the 2007 maximum. According to the forecast (shown with open circles on the figure) the mass deficit will increase during the next five days. Calculations by NASA, based on data from OMI, shows an ozone mass deficit of around 32.5 megatonnes, which is about half a megaton over the maximum calculated in UV radiation UV radiation is measured by various networks covering the southern tip of South America and Antarctica. There are stations in Southern Chile (Punta Arenas), southern Argentina (Ushuaia) and in Antarctica (Belgrano, Marambio, McMurdo, Palmer, South Pole). Bulletin from the UV Network of the US National Science Foundation (NSF) Reporting period: 15 Aug - 11 Sep 2008 Synopsis UV levels at Antarctic sites and Ushuaia were small during the reporting period as the Sun s elevation is still low. The UV Index did not exceed 1.6 at Antarctic sites and 2.5 at Ushuaia. McMurdo Station, Antarctica McMurdo Station was affected by the ozone hole during the last three weeks. UV levels remained very low, however, since solar elevations were still below 8. The maximum UV Index observed during the last three weeks was 0.3. Palmer Station, Antarctica Total ozone at Palmer Station was below 220 DU on 21 August, between 29 August and 1 September, and between 9 and 11 September, according to GUV-511 measurements. UV levels remained small because the Sun did not rise by 23

24 more than 21 above the horizon. The maximum UV Index, observed on 9 September, was 1.6. Typical summer-time indices range between 8 and 10 with maximum indices exceeding 13. South Pole, Antarctica UV levels were still negligible since the Sun has not risen yet. Ushuaia, Argentina The edge of the ozone hole has not passed over Ushuaia yet. The smallest ozone column was 250 DU, observed by the GUV-511 radiometer on 3 September. The maximum solar elevation was 30. The UV Index remained below 2.5. Distribution of the bulletins The Secretariat of the World Meteorological Organization (WMO) distributes Bulletins providing current Antarctic ozone hole conditions beginning around 20 August of each year. The Bulletins are available through the Global Atmosphere Watch programme web page at wmo.int/pages/prog/arep/gaw/ozone/index.html. In addition to the National Meteorological Services, the information in these Bulletins is made available to the national bodies representing their countries with UNEP and that support or implement the Vienna Convention for the Protection of the Ozone Layer and its Montreal Protocol. Acknowledgements and links These Bulletins use provisional data from the WMO Global Atmosphere Watch (GAW) stations operated within or near Antarctica by: Argentina (Comodoro Rivadavia, San Martin, Ushuaia), Argentina/Finland (Marambio), Argentina/Italy/ Spain (Belgrano), Australia (Macquarie Island and Davis), China/Australia (Zhong Shan), France (Dôme Concordia, Dumont D Urville and Kerguelen Is), Germany (Neumayer), Japan (Syowa), New Zealand (Arrival Heights), Russia (Mirny and Novolazarevskaja), Ukraine (Vernadsky), UK (Halley, Rothera), Uruguay (Salto) and USA (McMurdo, South Pole). More detailed information on these sites can be found at the GAWSIS web site ( gawsis). Satellite ozone data are provided by NASA ( NOAA/TOVS ( noaa.gov/products/stratosphere/tovsto/), NOAA/SBUV/2 ( and ESA/Sciamachy ( Satellite data on ozone, ClO, HCl and a number of other relevant parameters from the MLS instrument on the Aura satellite can be found here: Potential vorticity and temperature data are provided by the European Centre for Medium Range Weather Forecasts (ECMWF) and their daily T 106 meteorological fields are analysed and mapped by the Norwegian Institute for Air Research (NILU) Kjeller, Norway, to provide vortex extent, PSC area and extreme temperature information. Meteorological data from the US National Center for Environmental Prediction (NCEP) are also used to assess the extent of PSC temperatures and the size of the polar vortex ( shtml). NCEP meteorological analyses and climatological 24

25 Acknowledgements and links data for a number of parameters of relevance to ozone depletion can also be acquired through the Ozonewatch web site at NASA ( Ozone data analyses and maps are prepared by the World Ozone and UV Data Centre at Environment Canada ( by the Royal Netherlands Meteorological Institute ( nl/protocols/o3global.html) and by the University of Bremen ( UV data are provided by the U.S. National Science Foundation s (NSF) UV Monitoring Network ( UV indices based on the SCIAMACHY instrument on Envisat can be found here: Ultraviolet radiation data from the Dirección Meteorológica de Chile can be found here: Data on ozone and UV radiation from the Antarctic Network of NILU-UV radiometers can be found here: The Executive Summary of the 2006 WMO/UNEP Scientific Assessment of Ozone Depletion can be found here: Questions regarding the scientific content of this Bulletin should be addressed to Geir O. Braathen, mailto:gbraathen@wmo.int, tel: The next Antarctic Ozone Bulletin is planned for 10 October