British Antarctic Survey
The ozone hole is decreasing in size, though central values are still below 120 DU. Its shape varies with planetary wave activity. Ozone values over Weddell Sea areas are past minimum but still 50% below normal. Ozone values over the Antarctic Peninsula vary according to the position of the ozone hole and are currently only a little below normal.
1. Data from the British Antarctic Survey (BAS) Halley station (76-deg south, 26-deg west, on the Brunt ice shelf).
a) Ozone. Total ozone values fell from an estimated 300 DU in early July to around 200 DU in mid August. Values rose to around 240 DU towards the end of August but then steadily fell to 115 DU in early October. Ozone values are now rising and have reached 160 DU. Day to day variation is around 5 DU. Ozone values are comparable to those of last year, where the initial rise was followed by a plateau at about 160 DU. They are well below the long-term mean, with depletion at around 50%. The station is currently near the edge of the polar vortex.
Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1997 May 2 and minor revision 1997 September 26 and 1997 October 17.
(0 indicates no data)
1997 August 1 - 1997 October 23
154 125 117 121 122 118 113 115 125 114
114 117 128 121 117 120 123 144 148 163
162 150 165
b) Radiosonde data. Data from Halley show that the mean 100 hPa temperature is beginning to rise from winter values of -83°C and has now reached -76°C, which is on the lower boundary of the long term range and 6 C° below the long term mean. Stratospheric clouds, which are instrumental in the mechanism of ozone depletion, have been observed from the station on August 1, 3, 6, 7, 8, 10, 13, 14, 15, September 3, 4, 21, 22, 26, 27 and 30. The display on August 10 was particularly vivid and that of September 30 showed classic development after sunset.
Data from the British Antarctic Survey (BAS) Rothera station (68-deg south, 68-deg west on Adelaide Island).
a) Ozone. Ozone measurements from Rothera are made using a SAOZ (Systeme d'Automatique Observations Zenithales) spectrometer. This is a research instrument, but the daily ozone values are available. These show a generally similar pattern of variation to that seen at Vernadsky, though day to day variation is a little less and minimum values are a little lower.
Rothera preliminary mean daily total ozone, (DU)
(0 indicates no data or data not available)
1997 August 1 - 1997 October 20
200 196 172 205 283 338 351 359 330 297
257 200 193 241 216 186 206 204 201 211
181 159 152 133 131 145 157 153 133 136
120 137 134 138 153 187 199 222 290 346
Running mean total ozone values fell from an estimated 350 DU in early July to 240 DU in early August. Since then the running mean has varied between 150 and 300 DU (55 - 10% depletion) under the influence of planetary waves with a period of around a month. Day to day variation is currently around 40 DU. Particularly low values were recorded on August 2nd, when the station was affected by one of the ozone reduction events associated with the forming ozone hole, and on September 13th and October 4th and 11th when the centre of the ozone hole passed near the station. Very high values near 370 DU were recorded on September 18th when the circumpolar high ozone belt was over the station and were again rising around October 20th.
Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 October 7
1997 August 1 - 1997 October 18
200 184 153 205 269 355 369 371 371 286
268 213 185 253 249 217 244 261 263 241
225 197 174 149 150 160 200 181 158 168
150 159 156 149 155 192 235 233
TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center and EP/TOMS images from the US NASA/GSFC show the development of the ozone hole. The shape of the ozone "hole" varies in response to planetary wave activity. It is now past maximum extent and depth, and currently covers virtually the entire continent except part of West Antarctica and the Antarctic Peninsula. Minimum values at the centre of the hole lie around 120 DU. The normal circumpolar high ozone belt is present, with highest values over the tip of South America. UK Met Office analyses show that the polar vortex is centred approximately on 75-deg south, 90-deg east, and aligned roughly 65-deg south, 20-deg east to 65-deg south, 180-deg east on October 24. The edge of the ozone hole passed over the tip of South America and the Falkland Islands on September 13/14 and October 12/15 and just clipped the area on September 23/24 and October 4/5.
Further information is available on the BAS ozone web page, which contains earlier bulletins, data, graphs and general ozone information. The url is:
http://www.nbs.ac.uk/public/icd/jds/ozone
Note that all ozone values in this bulletin are preliminary and are subject to revision from time to time when the instrument constants are re-evaluated. Final data will be archived with WOUDC, Toronto in due course, but preliminary data back to 1973 are available from BAS on request. All Dobson ozone data is reduced to the Bass-Paur scale as recommended by the WMO. If you use or pass on this data please make acknowledgement to J D Shanklin, British Antarctic Survey.