Antarctic Ozone Bulletin No 3 / 2006
30
Belgrano
Altitude [km]
25 20 15 10 2 August: 233 DU 6 September: 150 DU 20 September: 141 DU
5 0
0
2
4
6
8
10
Ozone partial pressure [mPa]
12
14
Ozone soundings from the Argentinian GAW station Belgrano (78°S, 35°W). One can see the progression of ozone depletion from 2 August until 20 September. In the height region most affected by ozone destruction, the depletion amounts to about 80%. The ozone hole is expected to deepen further over the next couple of weeks. The soundings are carried out as a collaboration between Argentinian researchers and scientists from the Spanish Instituto Nacional de Tecnica Aeroespacial (INTA).
Executive summary Since the last Bulletin (12 September) vortex minimum temperatures at 50 hPa continue to remain around 181-182 K, which is well below the frost point and colder than for any year in the 1979-2005 period for this time of the year. The average temperature in the 60-90°S region has increased slightly, from 193 K to 194 K, but is lower than any other year since 1979 for this time of the year. The area where temperatures are low enough for existence of polar stratospheric clouds of type I (NAT) at the 450 K isentropic level (~17 km or ~70 hPa), has continued to decline from its peak (28.9 million km2) in late July to about 21 million km2 on 18 September. Since early July, the south polar vortex has been larger than the 1996-2005 average at the 450, 550 and 650 K isentropic levels. At 450 K, the vortex area has on certain days been as large as the maximum for the 1986-2005 time period. Chlorine activation reached its peak around 1 September and is now declining. There is still a region inside the vortex where hydrochloric acid (HCl) is completely depleted, which is an indication of complete activation. Ozonesonde observations show up to 90% ozone loss in the 15-20 km altitude range by 20 September compared to early August. The area where total ozone is less than 220 DU (also called the "ozone hole area") was relatively small until around 20 August. Since then the ozone hole area has increased more rapidly than the 1979-2005 average and is now close to 28 million km2, which is more than the maximum reached in 2005 (26 million km2) and very close to the maximum reached in 2003. It is still somewhat lower than the ozone hole area in 2000, which peaked at 28.5 million km2 on 10 September. Measurements of total ozone at individual stations and total ozone maps synthesised by the World Ozone and UV Data Centre show that total ozone columns in August and the first half of September were somewhat larger in 2006 as compared to the same time of the year in 2005. The last few days, ozone columns at most stations have dropped rapidly and are now the same as at the same time in 2005. Minimum total ozone columns from satellite observations have dropped rapidly the last days and are now near and even below the values observed in 2005. Predictions based on meteorological forecasts indicate that the vortex will remain relatively concentric and unperturbed, and it is not likely that areas outside Antarctica will be significantly affected by the ozone hole between now and 30 September. The intensity of ultraviolet radiation remains modest, with UV indices not exceeding 3.1 in southern Chile and Antarctica. As ozone depletion continues and the solar elevation increases, UV indices are expected to increase.
22 Sep. 2006
G l o b a l A t m o s p h e r e Watch
Introduction For background information on the Antarctic ozone hole and ozone loss in general the reader is referred to Bulletin no. 1/2006, which can be found here: http://www.wmo.int/web/arep/ozone.html
More background information is also found here:
http://www.wmo.int/web/arep/O3_summaries/O3_summaries_afischer.html.
Meteorological conditions Temperatures
Figure 2. Temperature at 50 hPa averaged over the area south of 60°S (until 20 September). This graph shows that this mean temperature has been unusually cold this year and since early September colder than any year since 1979. The graph is downloaded from the Ozonewatch web site at NASA.
As shown in Figure 1, minimum temperatures south of 50°S have been below the 1979-2005 average since early August and lower than ever during this time period since mid September. This is one of several parameters which indicates that the 2006 south polar vortex is less perturbed than usual.
PSC Area
The temperature averaged over the entire area south of 60°S is shown in Figure 2. It can be seen from the figure that this average temperature has been unusually low in 2006. Since early September, this average temperature has been colder than any year since 1979. This is an indication of an undisturbed and stable vortex.
230 220
Since the last Bulletin, the area with temperatures low enough for formation of PSCs of type I has continued to decrease as expected since the sun is now coming back to the south polar region. The PSC area at 450 K reached a maximum of 28.9 million square kilometres on 31 July and by 18 September it was down at 21 million km2. Since late July, the PSC area has been considerably higher than the 1986-2005 average and on several days as high as
50-90°S Minimum Temperature 50 hPa
30
HNO3 = 6 ppbv, H2O = 4 ppmv
200
Area [106 km2]
Tmeperature [K]
25
210
Type I PSC
190
Type II PSC
180 170
2006 2005 1979-2005
10%-90% 30%-70%
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
20
2003 2004 2005 2006 Mean 86-05 Max 86-05 Min 86-05
15
10
5
Figure 1. Time series of daily minimum temperatures at the 50 hPa isobaric level south of 50°S. The thick red curve shows 2006 (until 20 September). The blue line shows 2005. The average of the 1979-2005 period is shown for comparison in black. The thin grey lines represent the highest and lowest daily minimum temperatures in the 1979-2005 time period. 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 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.
0
May
Jun
Jul
Aug
Sep
Oct
Nov
Figure 3. Time series of the area where temperatures are low enough for the formation of PSCs of type I at the 450 K isentropic level. This corresponds to an altitude of approximately 17 km. The thick red curve shows 2006 (until 18 September). The blue, green and cyan curves represent 2005, 2004 and 2003, respectively. The average of the 1986-2005 period is shown for comparison in grey. The two dashed black lines show the maximum and minimum PSC area during the 1986-2005 time period for each date. The plot is based on data from NOAA's Climate Prediction Center.
ECMWF Analysis of PV (10-6 Km2/kgs) Θ = 500 K 20 Sep 2006 12 UT Day number 263 Plotted at NILU by t106glob
Figure 5. 45-day mean heat flux averaged over the region from 45°S to 75°S. The heat flux is calculated by correlating the meridional wind (north-south wind) and temperature. The heat flux is almost always poleward. That is, in the southern hemisphere the warm temperatures are transported southward by the meridional wind, while cold temperatures are transported northward. This polar warming by the heat flux is compensated by an upward Eulerian circulation that acts to cool the polar region. In this plot only the first three wave numbers are used. These lower wave numbers usually contain most of the wave energy and have an even stronger relationship to the polar cap temperatures. It can be seen that the heat flux has been relatively small in 2006 (between the average and the zero line), which is an indication of a stable and undisturbed vortex. In September the mean heat flux has been considerably smaller than the 1979-2005 average. This plot is downloaded from the Ozonewatch web site at NASA.
Figure 4. Polar orthographic map of potential vorticity (PV) at the potential temperature level of 500 K (ca. 20 km) over the south polar region for 20 September 2006. Although somewhat elongated, the polar vortex remains relatively concentric around the South Pole and its area is large in comparison to recent years. The plot is based on data from the European Centre for Medium range Weather Forecasts (ECMWF) and PV is calculated and plotted with tools developed at the Norwegian Institute for Air Research (NILU).
the maximum for any year during this time period. As of 18 September, the PSC area is still considerably higher than usual for this time of the year. This is shown in Figure 3.
Vortex size and stability Figure 4 shows a map of potential vorticity (PV) at the 500 K potential temperature level (~ 20 km) for 20 September 2006. This picture 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 previous Bulletin showed a PV map for 7 September. Comparing these two dates it can be seen that the vortex is still concentric around the pole, although somewhat more elongated. The longitudinally averaged heat flux between 45°S and 75°S is an indication of a disturbed stratosphere. Figure 5 shows this heat flux at 100 hPa averaged over 45 days. It can be seen from this figure that the heat flux so far this winter/spring has been smaller than the average. The figure shows that in mid September only 10% of the winters since 1979 have had a smaller averaged heat flux. This shows that the vortex has been relatively stable and undisturbed in 2006. In order to get an idea of the vortex develop-
Figure 6. Daily heat flux averaged over the region from 45°S to 75°S (until 20 September). See caption of Figure 5 for an explanation of the heat flux. Although varying considerably from day to day it can be seen that the heat flux has been relatively small in 2006. This plot is downloaded from the Ozonewatch web site at NASA.
ment over the next days it is better to look at the daily heat flux and this is shown in Figure 6. Although varying considerably from day to day, it can be seen that the heat flux has been relatively small in 2006,
30
Area [106km2]
25
2003 2004 2005 2006 ave 86-05 max 86-05 min 86-05
Minimum Ozone Column in the Southern Hemisphere 250
Dobson Units
35
20 15
150
100
10
GOME / SCIAMACHY/OMI Assimilated Ozone KNMI / ESA 21 Sep 2006
5 0
200
50 01 Aug
Apr May
Jun
Jul
Aug
Sep
Oct
Nov
01 Sep
01 Oct
01 Nov
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 fc OMI 2006 01 Dec
31 Dec
Figure 8. Daily minimum total ozone columns in the Southern Hemisphere as observed by GOME, SCIAMACHY and OMI from 1997 to now. The black dots show the SCIAMACHY observations for 2006. The open circles are forecasts for the next few days. The red dots show the OMI observations for 2006. The minimum ozone columns are now nearly as low as they have ever been during the 1997-2005 time period. The OMI data show somewhat lower minimum ozone columns than SCIAMACHY since OMI looks deeper into the vortex. The plot is provided by the Netherlands Meteorological Institute (KNMI).
Dec
Figure 7. Time series of the area of the south polar vortex at the isentropic level of 450 K (~17 km). The area is defined as the region where potential vorticity is less than -32�10-6 Km2/ kgs. The thick red curve shows 2006 (until 18 September). The blue, green and cyan curves represent 2005, 2004 and 2003, respectively. The average of the 1986-2005 period is shown for comparison in grey. The two thin grey lines show the maximum and minimum vortex area during the 1986-2005 time period for each date. The plot is based on data from NOAA's Climate Prediction Center.
AURA. Minimum ozone columns are close to the lowest minimum ozone columns observed during the 1979-2005 time period. Minimum ozone columns are expected to continue to decrease for another couple of weeks since the sun is now coming back to the south polar region and since the vortex is primed for ozone depletion.
in particular during the latter half of August. The last days (until 20 September), the heat flux remains relatively low and this indicates that the vortex will remain unperturbed the next few days. Figure 7 shows the daily geographical extent of the south polar vortex at the isentropic level of 450 K (~ 17 km) and it can be seen that the size of the vortex has been slightly higher than the 1986-2005 average since mid May. Since the beginning of August, the vortex area has risen more rapidly than usual and by mid August the vortex area was as large as the maximum for the 1986-2005 period. Since the last Bulletin, the vortex area at this level has continued to grow, and it reached a maximum of 34.6 million km2 on 14 September. For mid September, the 2006 south polar vortex is one of the largest since 1979. 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.
Balloon observations Belgrano Some of the recent ozone soundings carried out the Argentinian GAW station Belgrano are displayed on the cover of this Bulletin. The development from 2 August to 20 September is shown. At around 17 km, the ozone partial pressure has dropped from 12 to 2 mPa, which represents a depletion of more than 80%.
Neumayer Ozone soundings carried out at the German GAW station at Neumayer (70.65°S, 8.26°W) show clear signs of ozone depletion. Figure 9 shows ozone profiles observed on 5 August, 23 August, 9 September and 13 September. Due to fierce winds, it has not been possible to launch sondes after 13 September. The decline in the ozone column is around 50% from 5 August to 13 September. In the height region which is most severely affected (around 17 km), the degree of ozone destruction is around 90%.
Ozone observations Satellite observations Since the last Bulletin minimum total ozone columns inside the south polar vortex have dropped from about 150 DU to about 110 DU, as shown in Figure 8, which is based on data from the SCIAMACHY instrument on ENVISAT and the OMI instrument on
35
Neumayer
South Pole 12-20 km partial ozone column
13 September: 137 DU 9 September: 139 DU
30
23 August: 220 DU 5 August: 267 DU
Altitude [km]
25 20 15 10 5 0
0
2
4
6
8
10
12
14
Ozone partial pressure [mPa]
16
Figure 11. Partial column of ozone in the 12-20 km height range. The brown diamonds represent 2006 and a selection of previous winters are shown for comparison. Since late August the ozone depletion has been rapid and the partial column on 9 and 15 September is smaller than at the same date for any of the other years shown here. The 12-20 km range has been chosen since this is the altitude range where ozone depletion is the most severe.
18
Figure 9. Ozone partial pressure profiles measured with ozonesondes from the German GAW station at Neumayer (70.7°S, 8.3°W). The green profile shows the situation on 5 August, which was before any noticeable ozone depletion had taken place. The blue profile was observed on 23 August, and there are clear signs of ozone depletion. The red profile is from 9 September and the black profile is from 13 September. The total columns have been deduced by integrating the profiles from the ground to the burst point and then assuming a constant ozone mixing ratio from the burst altitude to the top of the atmosphere.
South Pole Figure 10 shows recent ozonesonde profiles taken at the NOAA GAW station at the South Pole. From 9 September (the most recent profile shown in the previous Bulletin) until 18 September the total column has decreased by about 22 DU. The change in total ozone from 15 to 18 September is very small, but ozone destruction is expected to continue during the next few weeks. Figure 11 shows the temporal development of the partial column of ozone in the 12-20 km altitude range. Since the last Bulletin the partial column (1220 km) has dropped from about 60 to about 40 DU.
South Pole
Marambio Ozonesonde observations from the Argentinian GAW station Marambio are shown in Figure 12. The change in the ozone profile from 30 August to 20 September is clearly visible. At 20 km, ozone is reduced by approx. 80%.
Ground-based observations WOUDC maps The total ozone maps synthesised by the World Ozone and UV Data Centre (WOUDC) are based on ground-based data. Preliminary near real-time data from ground-based observations are used for the most recent maps. In data sparse areas satellite data are used to fill in the gaps. Figure 13 shows
Figure 10. Ozone profiles from the NOAA/GMD GAW station at the South Pole. The black curve shows the situation on 18 September. Ozone depletion is evident when compared to the pre-ozone hole average curve (blue line).
30
of 20 September, the depth of the 2006 ozone hole is very similar to 2005. As shown below, the are of the 2006 ozone hole has surpassed the one of 2005. The stable and concentric vortex in 2006 limited the exposure to sunlight early in the season. As the sun has been coming back to the entire south polar region, ozone depletion has set in as expected.
Marambio
Altitude [km]
25 20 15 10 5 0
Some individual stations
30 August: 204 DU 2 September: 207 DU 6 September: 215 DU 9 September: 168 DU 20 September: 140 DU
0
2
4
6
8
Ozone partial pressure [mPa]
Results from some measurements sites will be shown here, but there is not enough space to bring results from all the stations in the region. Figure 14 shows the Dobson measurements at the Argentinian GAW station Marambio for 2004, 2005 and 2006. It can be seen that total ozone in August (before day 244) was higher in 2006 than in 2005, but during September ozone has dropped and is now (20 September) close to the total ozone measured at the same time last year.
10
Figure 12. Ozone profiles measured at the Argentinian GAW station Marambio (64.2°S, 56.6°W). The development from 30 August (purple curve) to 20 September (black curve) is shown. In some height regions the amount of depletion is around 80%.
Figure 15 shows the total ozone measurements made by the Brewer instrument at the Argentinian GAW station San Martin. Since the last Bulletin, total ozone values have dropped rapidly and are now well below the 2002-05 average.
WOUDC maps for 10 September (which was also shown in the previous Bulletin) and for 20 September. One can see that the area affected by ozone hole values (total ozone < 220 DU) has increased somewhat, but even more visible is the deepening of the ozone hole, as seen from the large increase in the area where total ozone is below 150 DU. If one compares with the corresponding map from 20 September 2005, it can be seen that the area of the ozone hole is similar, and total ozone values are approximately the same. In previous bulletins this year one has seen that the 2006 ozone hole has been smaller and shallower than the 2005 ozone hole. As
Figure 16 shows total ozone measured with the SAOZ spectrometer at the British NDACC-GAW station Rothera. With this instrument it is possible to measure around the year at this latitude, since the instrument is based on measurements at solar zenith angles around 90°. Since the previous Bulletin, total ozone has dropped quickly and is now (17 September) down to 103 DU. This is significantly lower than the 1996-2005 average for this time of the year
10 Sep 2006
20 Sep 2006
Figure 13. Total ozone maps of the southern hemisphere from the World Ozone and UV Data Centre at Environment Canada. The development from 10 (left) to 20 (right) September can be seen. The region with total ozone less than 200 DU (dark blue) has grown from 15 to 25 million km2 and the region with less than 150 DU (dark grey) has grown dramatically. There is also a region with less than 125 DU. These maps are based on ground-based data from the southern hemisphere in combination with satellite data from data sparse areas.
450
400
Marambio
400 350
Total ozone [DU]
Total ozone [DU]
350 300 250
2006
250 200
100
2005
150
50 120
2004 100 220
240
260
280
300
Day number
320
340
2006 2005 96-05 ave min max 170
220
270
Day number
320
Figure 16. Total ozone as measured with the SAOZ spectrometer at the British GAW station Rothera (67.6°S, 68.1°W). The red and blue curves show 2006 and 2005, respectively. The thick grey curve shows the 1996-2005 average and the thin black lines show the extreme values for each day during the years from 1996-2005.
360
Figure 14. Total ozone as measured with the Dobson spectrophotometer at the Argentinian GAW station Marambio (64.2°S, 56.7°W).
350
Chemical activation of the vortex
San Martin 300
Total ozone [DU]
300
150
200
Satellite observations The south polar vortex is now activated and primed for ozone depletion. The sun has come back to the entire vortex. Ozone depletion is evident in large parts of the vortex as seen in observations from the ground and from space. Figure 17 shows the extent of removal of hydrochloric acid (HCl), which is one of the reservoirs for active chlorine, for 5 and 16 September 2006. As can be seen from the figure, some HCl has come back in the outer regions of the vortex. However, in the core of the vortex there is less HCl on the 16th of September than on the 5th. This shows that activation has still been ongoing during this time period. Removal of HCl is an indicator of chemical activation of the vortex. See the figure caption for a more detailed description. Another indicator of vortex activation is the amount of chlorine monoxide (ClO). Figure 18 shows the amount of ClO on 5 and 16 September. The amount of ClO is quite similar on the two dates, but there is more ClO towards the centre of the vortex on the 16th. This is expected since a larger part of the vortex is sunlit. Figure 19 shows the mixing ratio of ozone at 490 K on the same two dates. Ozone depletion now affects the whole vortex. As the solar elevation increases, it is expected that the ozone mixing ratios will continue to decrease during the next weeks.
250
200
150
100
2006 Mean 2002-2005 50 220
Rothera
240
260
280
300
Day number
320
340
360
Figure 15. Total ozone as measured with the Brewer spectrophotometer at the Argentinian GAW station San Martin (68.1°S, 67.1°W). The grey curve shows the average values for the years 2002-05 and the red curve is for 2006.
as shown in the figure. At the other British station, Halley, one has just started the measurements and data from this station will be shown in later issues of the Bulletin.
Yet another indicator of chemical activation is the
HCl
5 Sep 2006
ppbv 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
HCl
16 Sep 2006
ppbv
Figure 17. Mixing ratio of HCl at the isentropic level of 490 K. The development from 5 to 16 September 2006 is shown. It can be seen that some HCl has come back in the outer parts of the vortex, with mixing ratios around 0.6 - 1.0 ppb. However, the region where virtually all HCl is converted to active chlorine has grown larger during these 11 days and the centre of the vortex is totally devoid of HCl. This means that ozone depletion will continue in this region for still some time to come. These maps are made at NASA's Jet Propulsion Laboratory and based on data from the Aura-MLS satellite instrument. The white contours indicate isolines of scaled potential vorticity.
O3
5 Sep 2006
ppmv 1.6 1.9 2.2 2.5 2.8 3.1 3.4
O3
16 Sep 2006
Figure 19. Mixing ratio of ozone at 490 K. The development from 5 to 16 September 2006 is shown. In the lower panel one can see how the ozone-depleted region now fills the entire vortex. These maps are made at NASA's Jet Propulsion Laboratory and based on data from Aura-MLS. The white contours indicate isolines of scaled potential vorticity.
ppmv
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
1.6 1.9 2.2 2.5 2.8 3.1 3.4 Figure 18. Mixing ratio of ClO at 490 K. The development from 5 to 16 September 2006 is shown. It can be seen that on both dates there are substantial amounts of ClO in most of the vortex, except for the inner parts. The white area around the pole indicates no data. On 16 September actiblack ppbv vation is more complete and SZA=94o reaches somewhat deeper into the vortex. Also note 0.15 0.45 0.75 1.05 1.35 1.65 how the inner edge of the ClO region follows the termi16 Sep nator (defined as SZA=94°). The white contours indicate 2006 isolines of scaled potential vorticity. The thick black contour line shows where the solar zenith angle is 94º. These maps are made at NASA's Jet Propulsion Laboratory and based on data from Aura-MLS.
5 Sep 2006
OClO SC @ 90˚ SZA [1014 molec cm-2]
ClO
ClO
black
SZA=94o
3.0
SCIAMACHY OClO Slant Columns
2002 2003 2004 2005 2006
2.5 2.0 1.5 1.0 0.5 0
IUP Bremen 5
10 15 20 25 30 July
5
10 15 20 25 30 August
5
10 15 20 25 30 September
5
10 Oct.
Figure 20. Vortex-averaged slant column OClO as observed by the SCIAMACHY instrument on ENVISAT. The degree of chlorine activation can be monitored by observing OClO, a molecule which is thought to be formed mainly by the reaction of ClO with BrO. As BrO amounts do not vary as much, OClO columns are in a first approximation proportional to ClO concentrations and therefore an indicator of chlorine activation. This graph shows that the degree of chlorine activation, as it develops over the course of the winter and spring, follows a fairly consistent pattern from one year to the next. The date of final deactivation has varied little from one year to another during the last four years and happens between 5 and 10 October. It can be seen from the figure that activation reached a maximum at the very beginning of September, but there is still (20 September) a considerable amount of active chlorine present in the vortex. This plot has been provided by Andreas Richter, Institute for Environmental Physics, University of Bremen, Germany.
ppbv
0.15 0.45 0.75 1.05 1.35 1.65
amount of chlorine dioxide, OClO. This compound is formed by the reaction of ClO with BrO. Figure 20 shows a figure of vortex averaged OClO. One can see that the OClO slant column reached a peak of around 2.8 · 1014 molecules/cm2 on 1 September and that it has now (20 September) decreased to 1.9 · 1014 molecules/cm2. As seen from the figure, it is quite likely that activation will cease around 10 Oc-
tober, and then ozone depletion will come to a halt. During the 20 days from 20 September to 10 October ozone depletion will continue and the ozone hole will deepen further.
ClOx (ClO + 2Cl2O2) at 456.650 K 5 Sep 2006
ClOx (ClO + 2Cl2O2) at 456.650 K 19 Sep 2006
Figure 21. Mixing ratio (ppb) of ClOx (the sum of ClO and two times the dimer, Cl2O2) at 456.65 K as modelled by the three-dimensional chemical transport model SLIMCAT at the University of Leeds. It can be seen that the area with high ClOx (above 3 ppb) has shrunk considerably from 5 to 19 September. The amount of ClOx shown in the right panel shows that there is still potential for ozone loss. See link to the SLIMCAT web site in the section on Acknowledgements and links.
% Ozone loss at 456.650 K 5 Sep 2006
% Ozone loss at 456.650 K 19 Sep 2006
Figure 22. Percent ozone loss at the 465.65 K isentropic level from the beginning of the winter until the actual date. On 5 September, the edge region has suffered almost complete ozone destruction at this level. There was still a region in the vortex core where ozone destruction has reached less than 40%. By 19 September almost the entire vortex has suffered more than 90% ozone loss. This results comes from the SLIMCAT chemical transport model (see previous figure).
Model results
30
Results from the SLIMCAT 3-dimensional chemical transport model at the University of Leeds are in accordance with the satellite observations. Figure 21 (previous page) shows the modelled amount of active chlorine (ClOx = ClO + 2 � Cl2O2) at the 456.65 K isentropic surface (approx. 17 km) on 5 and 19 September. It can be seen that the activated area has shrunk significantly between these two dates. Figure 22 shows the modelled amount of ozone destruction on 5 and 19 September. The white colour shows the region that has suffered more than 96% ozone loss at that level. According to the Slimcat calculations most of the vortex has suffered this much ozone loss. As the sun comes back to the vortex core, that region will also most likely suffer complete or near complete loss at this level.
NOAA
2000 2003 2005 2006
SBUV/2
Area [106 km2]
25
96-05 mean 96-05 max 96-05 min
20 15 10 5 0
Aug
Sep
Oct
Nov
Dec
Figure 23. Ozone hole area as derived from the NOAA satellite instrument SBUV/2. The red curve shows data for 2006 (until September 18). The blue curve shows 2005, the green curve 2004 and the purple curve 2000. The thick grey line shows the average for the 1996-2005 time period. The thin grey lines show the maxima and minima for this time period. Data for this plot was provided by Craig Long, NOAA.
Ozone hole area This issue of the Bulletin brings ozone hole area graphs based on three different satellite instruments; SBUV/2, OMI and SCIAMACHY. Figure 23 shows the area of the region where total ozone is less than 220 DU (ozone hole area) as deduced from the NOAA-operated SBUV/2 instrument. Figure 24 shows the ozone hole area as derived from the TOMS and OMI instruments. Figure 25 shows the ozone hole area as deduced from the GOME and SCIAMACHY satellite instruments. All three graphs show that the area of the ozone hole now has passed the maximum size reached in 2005. The KNMI forecast (Figure 25) for the next days indicates that the ozone hole area will continue to increase.
30
Ozone Hole Area
1979-2005 2005 2006
Area [106 km2]
10%-90%
The amount of ozone loss will be dependent upon prevailing meteorological conditions in the stratosphere during the next few weeks. The 2006 south polar vortex is relatively unperturbed, and although the ozone hole it is now very near its maximum area, it is likely that it will continue to deepen for another 2-3 weeks .
20
30%-70%
10
0
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 recently published 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.
Jul
Aug
Sep
Oct
Nov
Dec
Figure 24. Area (millions of km2) where the total ozone column is less than 220 Dobson units. 2006 is showed in red (until 18 September) and 2005 in blue. The smooth black line is the 19792005 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 1979-2005. The plot is adapted from a plot downloaded from the NASA Ozonewatch web site and is based on data from the OMI instrument on the AURA satellite.
10
on 17 September when total ozone was 150 DU. Typical summer-time UV Indices range between 8 and 10 with maximum Indices exceeding 13.
35 Ozone Hole Area w.r.t. 220 DU in the Southern Hemisphere
30
GOME / SCIAMACHY / OMI Assimilated Ozone KNMI / ESA 21 Sep 2006
Area [million km2 ]
25 20 15
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 forecast OMI 2006
South Pole, Antarctica: At the South Pole, the Sun is still below the horizon and UV levels remain negligible.
Ushuaia, Argentina:
10
Measurements with a GUV radiometer indicate that total ozone at Ushuaia did not drop below 250 DU during the last two weeks. UV levels therefore remained moderate. The maximum UV Index was 3.1.
5 0 01 Aug
01 Sep
01 Oct
01 Nov
01 Dec
31 Dec
Distribution of the bulletins
Figure 25. Area (millions of km2) where the total ozone column is less than 220 Dobson units. All the years from 1997 to 2006 (black dots) are shown. It can be seen that the 2006 ozone hole now has passed the maximum size reached in 2005 (black curve) and that it is very near the size of the 2003 ozone hole. The small open circles are forecasts and should be used with caution. The red dots are ozone hole areas based on data from OMI. This plot is produced by KNMI and is based on data from the GOME, SCIAMACHY and OMI satellite instruments.
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 http://www.wmo.ch/web/arep/ozone.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.
UV radiation NSF Network Latest bulletin, issued 20 September 2006. Reporting period: 6 - 19 September 2006.
Acknowledgements and links
Synopsis:
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 (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 (http:// www.empa.ch/gaw/gawsis).
All NSF network sites in Antarctica were affected by the ozone hole during the last two weeks, leading to relative increases in UV intensities. Absolute UV levels remained small because the Sun is still low in the sky. UV intensities at Ushuaia were not influenced by the ozone hole. The UV Index remained below 3.1 at all austral sites.
McMurdo Station, Antarctica: McMurdo Station was affected by the ozone hole during the last two weeks. UV levels remained very low because the Sun did not rise by more than 11° above the horizon. The maximum UV Index was 0.6.
Satellite ozone data are provided by NASA (http:// ozonewatch.gsfc.nasa.gov), NOAA/TOVS (http://www. cpc.ncep.noaa.gov/products/stratosphere/tovsto/), NOAA/ SBUV/2 (http://www.cpc.ncep.noaa.gov/products/stratosphere/sbuv2to/) and ESA/Sciamachy (http://envisat. esa.int). Satellite data on ozone, ClO, HCl and a
Palmer Station, Antarctica: Total ozone at Palmer Station ranged between 140 and 280 DU according to measurements with a GUV radiometer. Solar elevations remained below 24°. The maximum UV Index was 3.1 and was observed
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number of other relevant parameters from the MLS instrument on the Aura satellite can be found here: http://mls.jpl.nasa.gov/plots/mls/mls_plot_locator.php.
Map), by the Royal Netherlands Meteorological Institute (http://www.temis.nl/protocols/O3global.html) and by the University of Bremen (http://www.doas-bremen.de/).
UV data are provided by the U.S. National Science Foundation’s (NSF) UV Monitoring Network (http:// www.biospherical.com/nsf).
Potential vorticity and temperature data are provided by the European Centre for Medium Range Weather Forecasts (ECMWF) and their daily T106 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 (http://www.cpc.ncep.noaa.gov/products/stratosphere/polar/polar.shtml). NCEP meteorological analyses and climatological data for a number of parameters of relevance to ozone depletion can also be acquired through the Ozonewatch web site at NASA (http:// ozonewatch.gsfc.nasa.gov/meteorology/index.html).
Ultraviolet radiation data from the Dirección Meteorológica de Chile can be found here: http://www.meteochile.cl
The Executive Summary of the 2006 WMO/UNEP Scientific Assessment of Ozone Depletion can be found here: http://www.wmo.int/web/arep/gaw/gaw_home. html
Questions regarding the scientific content of this Bulletin should be addressed to Geir O. Braathen, mailto:
[email protected], tel: +41 22 730 8235. The next Antarctic Ozone Bulletin is planned for 6 October 2006.
Ozone data analyses and maps are prepared by the World Ozone and UV Data Centre at Environment Canada (http://exp-studies.tor.ec.gc.ca/cgi-bin/select-
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