Total ozone values are now rising at Halley and Vernadsky and the spring warming seems to be taking place. The ozone hole is decreasing in size and depth, but central values are still below 200 DU. Its shape varies with planetary wave activity and it is currently elongated from the Ross Sea to South Georgia. There are signs that it is breaking up. The southernmost South Atlantic experienced ozone values less than 240 DU over most of the past week. The next bulletin will be issued on December 5^th.


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 reach 115 DU in early October. Ozone values rose to around 160 DU late in October and remained near this value until mid November when the spring warming started. They are however, still well below the long-term mean, with depletion near 40%. Day to day variation is now around 40 DU.

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)

179 192 186 186 219 219 208 194 172 183

189 168 170 157 181 179 146 154 167 172

161 155 137 133 128 139 146 131 123 123

154 125 117 121 122 118 113 115 125 114

114 117 128 121 117 120 123 144 148 163

162 150 173 188 178 166 163 154 147 142 157

153 144 155 153 172 161 161 164 160 160

161 159 162 182 181 187 202 225 238 249

b) Radiosonde data. Data from Halley show that the mean 100 hPa temperature rose from winter values of -83-deg C in mid October and reached a plateau at -75-deg C by the end of the month. The rapid spring warming began in mid November, but the 100 hPa temperature is still more than 15 degrees 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, 30 and October 2, 3, 6 and 7. The display on August 10 was particularly vivid and that of September 30 showed classic development after sunset. The display on October 2 showed similar features to those seen in noctilucent clouds.

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 November 18

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

181 159 152 133 131 145 157 153 133 136

120 137 134 138 153 187 199 222 290 346

357 329 348 360 340 324 284 201 156 153 142

130 133 150 157 168 183 157 155 145 146

141 150 153 175 186 218 238 271

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 340 DU (55 - 5% depletion) under the influence of strong 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 2^nd, when the station was affected by one of the ozone reduction events associated with the forming ozone hole. Very low values occurred around September 13^th, October 4^th, 11^th and November 1^st (142 DU is the lowest November daily mean on record for the station) when the centre of the ozone hole passed near the station. Very high values near 370 DU were recorded on September 18^th and October 21^st 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 November 8

No new data has been received this week.

268 213 185 253 249 217 244 261 263 241

225 197 174 149 150 160 200 181 158 168

150 159 156 149 155 192 235 233 329 368

362 355 364 363 341 341 321 274 193 184 170

142 151 162 181 195 227 221 169

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 well past maximum extent and depth and has become very thin and elongated. It currently extends from the edge of the Ross Sea to South Georgia. Minimum values at the centre of the hole are still below 200 DU. Much higher ozone levels are pushing in at around 90-deg west, 140-deg east and 40-deg east. The normal circumpolar high ozone belt is present, and ozone values are highest south of Africa and Australia and New Zealand. UK Met Office analyses show that the polar vortex is beginning to fragment with centres at approximately on 55-deg south, 10-deg west, and 80-deg south, 160-deg west on November 21. The lowest temperature at the 100 hPa level has risen to around -66-deg C. The edge of the ozone hole passed over the tip of South America and the Falkland Islands on September 13/14, October 12/15, October 31/November 5 and November 10/13 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.