The ozone hole is near maximum development, with central values below 120 DU and has become more circular in shape. Ozone values over Weddell Sea areas are now declining more slowly and are 60% below normal. Ozone values over the Antarctic Peninsula vary according to the position of the ozone hole. The edge of the ozone hole brushed the tip of South America and the Falkland Islands over October 4 to 5.


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 120 DU in early October. The decline is now levelling out. Day to day variation is around 10 DU. Ozone values are comparable to those of the past few years, but well below the long-term mean, with depletion at around 60%.

Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1997 May 2 and minor revision 1997 September 26.
(0 indicates no data)

194 0 194 195 213 214 221 215 230 217

0 0 0 0 0 0 221 251 210 194 187

179 192 186 186 218 218 205 191 170 178

184 163 167 155 176 174 141 149 165 171

161 154 137 128 127 138 145 128 118 123

149 125 114 118 119 116 114 112 123

Halley provisional monthly mean total ozone (DU)

b) Radiosonde data. Data from Halley show that the mean 100 hPa temperature increased substantially towards the end of August, from close to the long term norm of -83 deg C, to -78 deg C, near the upper limit of the long term range. The temperature then dropped to near normal and has since varied between -84 deg C and -79 deg C in response to planetary waves. It is currently -82 deg C compared to the long term norm of -76 deg C. 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 and 15. The display on August 10 was particularly vivid.

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 6

301 297 309 312 304 266 279 272 256 259

259 294 287 292 266 266 297 304 295 270 236

230 199 214 248 259 244 216 194 204 203

200 196 172 205 283 338 351 359 330 297

257 200 193 241 216 186 206 204 201 211

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 200 and 300 DU (40 - 10% depletion) under the influence of planetary waves with a period of around a month. Day to day variation is currently around 100 DU. Particularly low values were recorded on August 2^nd, when the station was affected by one of the ozone reduction events associated with the forming ozone hole, and on September 13^th and October 4^th when the centre of the ozone hole passed near the station. Very high values near 370 DU were recorded on September 18^th when the circumpolar high ozone belt was over the station.

Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 October 7

1997 August 1 - 1997 October 4

255 257 275 285 285 254 239 237 235 248

236 298 291 296 258 287 314 312 305 300 253

237 200 205 255 254 251 232 213 211 208

200 184 153 205 269 355 369 371 371 286

268 213 185 253 249 217 244 261 263 241

225 197 174 149

Vernadsky provisional monthly mean total ozone (DU)

TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center and EP/TOMS images from the US NASA/GSFC show the developing ozone hole. Intermittent ozone reduction events occurred during late July and early August. The ozone "hole" is near maximum extent and depth and has become more circular in shape. Minimum values at the centre of the hole lie below 120 DU, but ozone values are high over the continental edge at around 120-deg east. The normal circumpolar high ozone belt is present, with a very elongated high south of Australia and a small high on the tip of South America. UK Met Office analyses show that the slightly elongated polar vortex is centred approximately on 77-deg south, 30-deg east, and aligned roughly 55-deg south, 30-deg east to 70-deg south, 140-deg west on October 8. The analyses and the radiosonde profiles from Halley and Neumayer show that a strong warming event occurred over the Weddell Sea area at the end of August as the centre of the vortex displaced towards the Pacific. The edge of the ozone hole passed over the tip of South America and the Falkland Islands on September 13/14 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.