British Antarctic Survey

British Antarctic Survey
Ozone Bulletin 18/97 issued 1998 May 25

Overall the 1997/98 ozone season was comparable to those of recent years, with minimum ozone values of around 110 DU at Halley. The spring warming took place slightly earlier than in the past two years, leading to a higher annual mean. The January and February means for Vernadsky were the lowest on record. The 100 hPa temperature over Halley and Vernadsky was below the long term mean for most of the season. The first bulletin of the 98/99 season will be issued in August.

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. Summer values declined to a plateau in early January at around 260 DU. Daily variation began to increase at the beginning of March, although mean values have changed little. Ozone values remained significantly below the long term mean throughout the year.

Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1998 April 6.
The revision has generally changed values by less than 3%
(0 indicates no data)

1997 August 11 - 1998 April 2

199 0 199 200 218 219 225 219 234 220

0 0 0 0 0 0 232 261 222 206 198

191 204 197 197 228 228 215 200 176 186

193 170 172 161 183 182 148 155 170 175

166 160 141 134 132 142 149 133 124 127

156 128 119 123 124 120 117 117 127 116

115 119 130 123 118 123 126 147 151 168

166 154 177 191 182 169 167 157 150 145 160

157 148 158 156 176 164 165 168 164 164

166 163 166 188 186 192 207 231 244 255

265 264 244 237 262 270 279 301 282 266

272 278 278 294 303 309 296 299 312 295

302 292 302 304 279 254 247 282 289 297

287 297 292 284 279 274 272 266 276 277 283

284 282 284 270 273 267 267 252 251 258

260 262 258 269 277 263 261 280 295 258

252 252 263 280 276 281 259 255 263 260 251

245 261 261 267 257 265 269 280 286 257

252 258 257 267 261 262 252 249 261 261

263 280 272 257 273 253 249 260

261 258 262 264 296 261 268 276 287 280

280 280 300 264 261 258 264 269 297 239

229 233 255 250 260 273 247 251 258 248 253

261 260

Halley provisional monthly mean total ozone (DU)

Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1997/98 218 171 141 210 286 267 262 264 261 231
1996/97 173 155 148 181 260 278 265 247 243 217
1995/96 218 160 130 164 252 261 249 246 226 212
1957-72 295 285 300 355 350 320 300 295 285 310

Note that August and April do not have observations on every day, and that the routine measurement season is now longer than it was in 1957 - 72. Measurements made at the start of the season are of lower accuracy than in mid summer due to the low solar elevation. Gif images showing the data are available on the BAS ozone web-page.

b) Radiosonde data. Data from Halley show that the mean 100 hPa temperature began to rise 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 (around 20 days later than normal), and peaked at -39-deg C in early December. Summer values remained at around -43-deg C until early February when the decline to winter values began. The 100 hPa temperature remained significantly below the long term mean all summer and rarely exceeded it in the autumn decline.

Stratospheric clouds, which are instrumental in the mechanism of ozone depletion, were 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 April 30

299 216 227 199 239 211 218 299 285 270 301 297 309 312 304 266 279 272 256 259 259 294 287 292 266 266 297 304 295 270 236 230 199 214 248 259 244 216 194 204 203

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

141 150 153 175 186 218 238 271 312 323

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

282 283 278 284 287 288 280 284 280 283

276 280 278 265 237 257 255 254 257 255

242 244 249 250 255 262 264 256 257 251 250

246 256 0 255 247 255 258 244 240 239

247 250 260 264 261 267 262 257 261 247

260 263 266 260 0 0 277 268

274 267 283 298 299 297 289 300 289 280

273 274 296 297 294 294 276 273 288 282

279 262 280 274 282 289 276 273 270 274 300

312 327 326 301 309 294 305 287 261 261

303 299 297 327 286 298 333 316 301 303

323 312 266 285 267 294 289 272 256 278

b) Stratospheric clouds. Nacreous or mother-of-pearl clouds are regularly seen from stations along the Antarctic Peninsula between early May and October, with a peak in July. There is some evidence that their frequency of occurrence has increased since the mid 1950s. This year they were observed from Rothera on June 8, 10, 13, 15, July 4, 17, 21, 23, August 4, September 1, 3 and October 14. The first display of the 1998/99 season was seen on May 20, with suspected clouds also seen on March 28 and April 21.

3. Data from the Ukrainian Antarctic Research Centre Vernadsky station (65-deg south, 64-deg west on the coast of the Antarctic Peninsula, formerly the BAS Faraday station).

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. Values slowly declined through the summer, but began to rise at the end of February as the autumn circulation took hold. A marked drop, associated with a drop in 100 hPa temperature, took place at the end of April.

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 1998 April 3

The revision has changed mean values by less than 2%.

1997 August 1 - 1998 April 30

276 217 238 228 229 233 226 274 268 254

245 247 266 279 280 251 234 234 230 243

233 294 287 292 256 285 311 311 304 300 254

237 200 207 257 255 254 234 214 213 209

201 185 156 207 273 359 375 379 378 291

271 216 187 258 254 221 249 267 269 247

230 200 177 150 150 161 203 183 158 170

151 161 157 149 157 195 240 238 339 379

373 364 374 369 350 349 328 280 196 186 171

143 151 162 182 198 232 224 170 164 155

157 169 167 167 188 199 231 283 328 329

325 332 303 299 341 331 321 306 325 314

318 286 283 292 292 289 292 295 304 305

302 316 315 306 290 293 296 297 300 300

295 283 290 293 308 296 308 302 298 288 290

276 286 289 292 295 291 290 298 303 291

289 291 281 278 286 291 282 300 283 293

285 264 252 256 265 270 276 268 266 260 267

251 252 268 289 268 266 268 261 236 243

261 270 280 273 258 259 242 250 272 249

256 268 276 273 287 290 308 282

271 275 263 292 294 293 301 283 300 272

272 262 250 281 292 291 296 276 280 290

299 276 246 270 265 280 272 277 269 276 310

285 323 329 305 308 281 306 286 249 247

277 285 272 292 276 283 320 328 295 287

309 301 247 261 240 256 245 247 248 241

Vernadsky provisional monthly mean total ozone (DU)

Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1997/98 261 251 235 240 297 281 266 280 281 266
1996/97 208 203 265 225 272 307 281 277 283 258
1995/96 240 199 252 230 296 284 285 276 264 258
1957-72 310 330 345 370 345 320 300 295 310 325

Note that the routine measurement season is now longer than it was in 1957 - 72. Measurements made at the start of the season are of lower accuracy than in mid summer due to the low solar elevation and are probably too low. Gif images showing the data are available on the BAS ozone web-page.

b) Radiosonde flights at Bellingshausen resumed in mid November and show a rapid rise in temperature at the 100 hPa level, peaking at -44-deg C in mid December. Values began to decline slowly in mid January, generally remaining below the long term mean. Unusually low values were seen at the end of April.

4. Information from other sources.

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 values then declined after the summer peak. The ozone distribution is now in its normal winter pattern.

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. The estimated accuracy of the daily means is better than 5% for solar elevations greater than 10 degrees and better than 10% otherwise. 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