British Antarctic Survey
Total ozone values are slowly declining at Halley and Vernadsky following the spring peak but have remained 15 - 20% below the long term mean. The 100 hPa temperature over these stations is a few degrees below the long term mean. Overall, development of the 1997 ozone hole was similar to previous years, with maximum depletion of around 60%. Long period planetary wave activity, as shown by the Vernadsky ozone data, was stronger than seen recently and was comparable to that seen in 1986, although ozone values this year were lower. The next bulletin will be issued in early March.
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. Values peaked at just under 300 DU in early December, compared to the long term mean peak of 380 DU. Since then values have declined to around 260 DU. This is well below the long-term mean, with depletion near 20%. Day to day variation is now around 20 DU.
Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1997 December 5.
(0 indicates no data)
1997 August 1 - 1998 January 8
194 0 194 195 213 214 221 215 230 217
0 0 0 0 0 0 217 247 206 190 183
175 188 182 182 215 215 206 191 170 182
188 166 169 156 179 177 145 152 167 172
162 155 137 132 128 140 146 130 121 124
153 125 116 121 121 117 114 115 124 113
113 116 127 120 116 120 123 144 147 162
163 151 173 187 178 166 163 154 147 142 157
153 145 155 152 172 161 161 164 160 160
161 159 162 182 181 188 203 226 239 250
261 262 243 234 261 267 275 300 281 264
271 277 273 290 300 306 292 293 310 292
299 288 296 301 275 249 242 278 285 294
283 294 288 280 275 270 268 261 271 272 279
278 277 279 266 269 262 262 249
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, and peaked at -42-deg C in early December. A slow decline has already started, with the 100 hPa temperature now substantially (5 deg 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, 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 - 1998 January 6
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
141 150 153 175 186 218 238 271 312 323
314 318 306 275 278 321 310 310 299 302
292 280 284 284 285 293 291 301 308 310
309 309 304 294 283 290 295 292 287 279
276 274 282 291 288 285 281 278 276 0 0
282 283 278 284 287 288
Running mean total ozone values fell from an estimated 350 DU in early July to 240 DU in early August. From then until early December the running mean varied between 150 and 340 DU (55 - 5% depletion) under the influence of strong planetary waves with a period of around a month. The spring warming produced a peak of around 320 DU, which is 20% below the long term mean and values are now slowly declining, but still 15% below the long term mean. Day to day variation is currently around 20 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. Very low values occurred around September 13th, October 4th, 11th and November 1st (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 18th and October 21st when the circumpolar high ozone belt was over the station.
Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 December 5
1997 August 1 - 1998 January 7
236 199 207 257 256 252 234 214 213 210
202 184 154 206 271 356 370 373 372 287
269 214 186 255 250 218 246 263 265 243
227 198 176 150 151 161 201 182 159 170
152 161 158 150 156 194 237 234 330 370
364 356 365 364 343 343 322 275 195 186 172
143 152 164 182 197 229 222 170 164 154
157 169 167 166 188 198 229 278 320 321
319 324 296 295 332 327 315 301 317 308
311 282 280 288 285 286 288 291 297 300
297 310 309 301 285 286 291 290 293 293
289 280 287 287 303 293 304 299 294 286 284
271 280 285 288 288 287 285
TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center and EP/TOMS images from the US NASA/GSFC show the development and break-down of the ozone hole. Development of stratospheric clouds in lee waves from the Antarctic Peninsula seems to have generated enhanced ozone depletion over the Weddell Sea in a number of events in the early stages of the ozone hole formation. The maximum extent of the ozone hole occurred as usual in the first week of October. Satellite images show that 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 10/15 and just clipped the area on September 23/24 and October 4/5. The rapid breakdown of the hole commenced in the week of November 17 and ozone values are now at their summer high over the Antarctic continent.
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.
Jon Shanklin