British Antarctic Survey

BAS Ozone Bulletin 04/00

(Annual Summary)

The 2000 ozone hole reached its greatest extent in early September at 28.4 million square kilometres and was the largest ever-recorded ozone hole. It reached this maximum extent unusually early, as the hole is normally largest in late September. Minimum ozone values were measured in early October and were amongst the lowest on record. The edge of the ozone hole passed over the tip of South America and the Falkland Islands for significant periods between October 6 and 24. The hole also closed in unusually early and the event was essentially over by early December. This early closure of the hole is probably linked with the QBO/ENSO and in retrospect was to be expected.

Satellite imagery gives a global perspective on the ozone hole. TOVS and TOMS currently have significantly different calibrations, with TOVS reading some 30 DU higher than TOMS. TOMS values are close to ground-based values. Our 2000/2001 ozone hole movies, produced from TOMS images, currently cover June 2000 to early May 2001. Stratospheric clouds were sighted from Vernadsky, Rothera and Halley. A mini ozone hole, with central values below 200 DU, periodically formed to the east of the Antarctic Peninsula over the Weddell Sea during July. This mini ozone hole probably formed due to processing of ozone through PSCs, which are far enough north to be sunlit. The feature was particularly marked on July 10 and again on July 20.

Ozone values over the Arctic are normally at their lowest in September and 2000 was no exception as can be see from the TOMS images. Although the values were low, they were low because of stratospheric dynamics and not chemistry. The temperature in the Arctic ozone layer was above –55 °C, far too warm for stratospheric clouds to form. Hence there was no chemical depletion taking place and no ozone hole above the Arctic. In mid October there were regions of low ozone over Siberia. Stratospheric temperatures in this area were generally above –65 °C, so again these features had a dynamic, not chemical origin. The temperature of the Arctic stratosphere did fall below the threshold for PSC formation at times in small regions during 2001 January and February. These regions developed ozone values lower than elsewhere in the Arctic, and in mid February values below 250 DU were recorded by TOMS over a small area of northwest Europe. Ozone values are currently high over most northern temperate and polar latitudes.

1. Data from the British Antarctic Survey (BAS) Halley station (76-deg south, 27-deg west, on the Brunt ice shelf).

a) Ozone. Ozone measurements in the first half of August were made using moonlight and are of very low accuracy.

Mean ozone values dropped from their winter level of around 250 DU to reach a low of around 110 DU in early October, 65% below the normal. The ozone hole closed unusually early, with column ozone values rising above 300 DU in mid November, although they dropped again later in the month. Maximum values around 330 DU occurred in early December, though mean values never reached those of pre ozone hole times, remaining some 15% below the normal. Values then slowly declined. Values briefly dropped to around 230 DU (25% below the normal) in late February for around a week. By the end of the observing season in mid April, values were at winter values of around 250 DU, some 15% below the long term mean.

Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1999 October 8.
(0 indicates no data)

2000 August 1 - 2001 April 30

0 0 0 0 0 0 0 0 0 201

151 174 182 0 0 165 153 149 0 0

0 0 0 0 0 0 255 188 165 180 179

189 184 196 192 199 206 183 167 152 170

172 165 167 155 138 143 152 129 127 123

135 134 129 129 120 110 121 114 108 107

118 119 120 124 112 112 105 120 119 119

121 131 135 125 119 123 129 141 139 138

138 150 160 159 154 168 164 173 171 164 164

188 241 267 271 235 205 261 279 295 292

284 284 285 280 293 302 321 300 264 278

247 279 292 283 271 236 220 227 248 281

307 305 330 323 316 317 317 322 329 316

301 292 299 294 300 318 299 296 287 298

300 293 285 277 283 276 273 271 274 290 293

286 282 287 282 295 286 293 277 280 281

287 291 274 278 272 286 307 274 282 289

296 290 298 294 294 291 294 283 281 283 279

281 282 280 270 279 277 258 261 263 274

280 258 255 252 284 271 260 257 258 270

270 251 256 252 251 227 224 218

225 228 231 218 233 247 224 238 283 257

248 245 257 242 251 245 249 245 244 252

245 233 244 255 253 261 275 263 287 312 301

250 248 246 251 228 240 217 223 242 256

278 264 253 238 247 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0

Halley provisional monthly mean total ozone (DU)

Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
2000/01 179 151 137 267 299 286 261 251 245 231
1999/00 205 172 143 172 254 281 258 250 256 221
1998/99 221 162 140 183 255 272 259 254 267 224
1997/98 218 171 141 210 286 267 262 264 261 231
1996/97 173 155 148 181 260 278 265 247 243 217
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 or use of moonlight. Gif images showing the data are available on the BAS ozone web-page.

b) Stratospheric clouds, which are instrumental in the mechanism of ozone depletion, were observed from the station on July 10, 12, August 2 and 22.

c) The 100 hPa temperature remained below –80 °C until mid October, then rose steadily to reach –50 °C in mid November. It dropped to reach –60 °C by late November, but then rose, reaching –40 °C in early December. It was below the normal from late September to the end of November and from mid December to late March.

2. 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 research instrument has a preliminary calibration such that it reads about 15% low compared to Dobson measurements at 100 DU, and is in agreement at 300 DU. The lowest values are around 105 DU once the 15% correction is applied to the measurements given below. The mean daily total ozone values generally show a similar pattern of variation to that seen at Vernadsky, though day to day variation does not show such pronounced wave activity and minimum values are a little lower.

Rothera preliminary mean daily total ozone, (DU)
(0 indicates no data or data not available)

2000 July 1 - 2001 April 30

273 249 276 0 0 288 236 205 144 173

225 279 264 245 225 232 243 225 201 246

225 178 213 201 225 233 245 0 242 220 246

232 211 228 203 228 240 231 246 246 286

298 252 226 217 238 241 0 0 188 196

179 175 184 220 193 232 262 287 273 258 202

195 208 193 184 187 162 127 111 114 108

138 128 121 115 0 0 124 111 94 92

104 119 101 98 111 120 110 127 198 225

189 149 136 124 120 125 137 134 139 0

0 105 100 112 117 110 104 114 119 130

124 139 164 260 234 259 296 327 244 259 299

0 353 355 365 355 355 353 361 354 339

335 323 337 357 0 342 338 328 334 354

351 336 308 308 299 291 307 307 303 305

277 292 300 0 326 329 319 302 293 298

307 304 296 293 283 288 292 291 292 293

290 292 296 296 290 279 280 287 279 267 274

275 279 292 287 283 279 289 287 273 268

266 270 273 272 271 272 275 262 0 257

256 256 259 268 278 270 274 272 273 270 273

301 295 292 302 296 280 285 290 290 275

278 281 286 275 271 273 277 276 272 277

264 259 0 279 268 247 251 263

273 264 262 260 252 267 276 269 267 274

289 311 291 283 283 292 288 0 0 261

265 257 265 277 279 276 288 316 321 308 277

261 241 0 0 260 242 249 287 296 296

308 289 278 266 264 274 288 263 279 295

310 293 272 292 286 315 277 246 275 0

Rothera provisional monthly mean total ozone (DU)

Period Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
2000/01 231 230 137 168 334 294 273 278 279 278
1999/00 274 243 157 175 229 289 282 265 264 290 282 293
1998/99 288 239 159 166 252 264 270 279 267 277 300 287
1997/98 270 280 267 263

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. During 2000 they were observed from Rothera on June 23, 26, July 10, August 21 and 22.

c) Noctilucent clouds were observed from the station on 2001 February 11. In addition I observed a good display of these clouds from off the Falkland Islands on 2001 January 15.

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).

a) Ozone. Lowest ozone values were reached in mid September and mid October, with the running mean reaching 140 DU (around 60% below the normal) and daily means reaching around 120 DU. The ozone hole closed unusually early, with near normal ozone values being reached in early November. Since then there has been a slow decline in column ozone, roughly paralleling the long term mean, and values are now around 280 DU, about 10% below the long term mean.

Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1999 October 25

2000 August 1 - 2001 April 30

255 245 265 236 248 263 252 246 246 286

277 255 213 213 229 252 245 205 214 207

198 192 204 238 196 219 258 291 316 298 242

239 237 213 209 195 177 148 141 142 147

164 138 130 145 141 164 160 133 119 118

120 158 134 139 149 148 131 157 187 271

259 245 225 169 161 160 156 158 187 139

132 128 121 132 138 144 131 130 145 155

144 149 180 240 269 260 304 358 292 285 297

344 354 367 357 372 378 374 370 364 359

336 330 321 367 344 351 347 348 333 348

361 364 324 327 317 295 313 321 306 312

299 312 329 315 327 329 323 316 308 311

311 305 298 297 309 293 307 289 295 299

298 318 302 324 312 306 304 300 304 294 301

310 316 317 311 291 277 292 276 280 281

292 296 288 300 288 295 303 288 281 282

284 276 286 301 301 296 296 305 295 284 304

312 304 309 309 298 287 292 294 293 279

271 305 298 283 290 285 287 282 278 268

266 276 270 274 252 252 265 271

275 268 283 277 268 269 267 261 266 271

283 316 280 289 286 249 285 268 257 263

257 255 262 265 297 280 303 319 334 316 291

268 270 244 262 275 250 254 268 298 288

299 299 285 284 262 269 297 253 286 304

307 285 270 283 291 322 248 235 266 260

Vernadsky provisional monthly mean total ozone (DU)

Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
2000/01 242 162 193 343 308 293 284 279 276 264
1999/00 249 189 202 283 297 292 271 262 293 260
1998/99 241 200 218 305 278 288 289 273 279 263
1997/98 261 251 235 240 297 281 266 280 281 266
1996/97 208 203 265 225 272 307 281 277 283 258
1957-72 310 330 345 370 345 320 300 295 310 325

b) Stratospheric clouds were seen from Vernadsky on 2000 June 19, July 8, 17, 18, 21, 26, August 4 and September 12, 21 and 22.

4. Information from other sources.

The use of data from TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center and EP/TOMS images is acknowledged.

Further information is available on the BAS ozone web page, which contains earlier bulletins, data, graphs and general ozone information. It is often updated several times a week during the ozone hole period. The email ozone bulletins have been issued less frequently this year so for the latest information see: http://www.antarctica.ac.uk/met/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 are reduced to the Bass-Paur scale as recommended by the WMO. The reference period used for the normals is 1957 - 1972. If you use or pass on data in this bulletin please make acknowledgement to J D Shanklin, British Antarctic Survey.