British Antarctic Survey

BAS Ozone Bulletin 01/01

The 2001 ozone hole reached an area of over 25 million square kilometres at its maximum, but it is now shrinking and filling. At around 18 million square kilometres in size, it is still significantly larger than at this time last year. The hole is offset from the pole, with lowest values, below 150 DU (50% depletion), over Dronning Maud Land and significant depletion extends towards Africa. The winter high ozone belt in the south temperate regions generally surrounds Antarctica, particularly over the Pacific sector.

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 are made using moonlight and are of very low accuracy. Some early Halley observations using moonlight gave total ozone values around 220 DU at the beginning of August, a depletion of about 25%. In September values dropped, from around 180 DU at the beginning of the month, at around 2 DU per day. From the equinox to late October values were around 125 DU, which is 60% below the normal. The minimum daily mean value recorded this year was 116 DU. Values are now increasing, but at 170 DU remain 50% below the normal.

Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 2001 October 26.
(0 indicates no data)

2001 August 1 – 2001 October 31

0 223 229 234 223 210 0 0 0 0

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 168 164 172 184

174 158 158 144 144 137 146 148 142 125

121 120 126 144 136 133 144 127 161 169

136 121 116 120 125 135 132 127 130 147

132 129 130 136 130 125 120 146 137 132

123 138 139 152 142 134 140 140 173 176 222

Halley provisional monthly mean total ozone (DU)

Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
2001/02 224 148 138
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
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) Radiosonde data. The 100 hPa temperature at Halley remained at winter values of around –83°C until late October. At -75°C it remains substantially below the normal (-62°C), but has undergone some warming in the last week. It was a few degrees below the normal for most of the first half of 2001, except for a short period between mid March and the end of April.

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. Rothera recorded sub 200 DU between July 27 and 29. Values generally declined from a peak of 340 DU at the beginning of July to 150 DU in mid September and climbed above 250 DU near the end of the month. They dropped to around 140 DU in mid October. 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)

2001 July 1 - 2001 October 22

321 329 304 311 334 316 314 345 348 316

311 291 324 0 0 268 265 258 285 279

285 227 253 294 293 270 196 194 187 211 272

0 264 254 223 270 259 245 214 255 255

289 277 259 259 234 232 233 258 283 0

0 266 206 199 205 229 185 213 192 205 214

206 199 177 246 246 200 186 170 171 169

0 0 160 168 203 154 150 198 131 124

159 231 319 311 294 260 196 230 263 222

218 0 178 192 193 183 195 175 164 156

136 149 139 144 136 152 160 144 129 125

130 157

Rothera provisional monthly mean total ozone (DU)

Period Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
2001/02 283 238 205
2000/01 231 230 137 168 334 294 273 278 279 278 280 276
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. This year, clouds were sighted from Rothera on August 3, 20, 27 and September 5, 6 and 25.

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. Ozone values at Vernadsky generally declined from about 280 DU at the beginning of August to around 210 DU (a depletion of about 35%) in mid September. A significant rise above 350 DU took place around the equinox, then values dropped to around 170 DU (a depletion of about 50%) in mid October. They rose to near normal values at the end of the month. There was considerable diurnal variation in the ozone readings at Vernadsky when the station lay under a strong stratospheric ozone gradient.

Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 2001 October 18

2001 August 1 – 2001 October 31

308 293 285 234 297 258 247 236 250 208

306 299 248 256 243 236 249 232 252 222

267 286 208 228 196 224 196 212 199 200 219

279 224 191 245 285 253 268 244 185 202

216 257 205 239 273 190 168 261 183 157

161 229 365 345 322 296 263 238 289 299

317 215 167 325 316 236 243 235 218 213

195 182 187 185 180 190 234 177 173 183

158 176 187 147 187 291 220 403 351 388 362

Vernadsky provisional monthly mean total ozone (DU)

Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
2001/02 245 244 234
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
1957-72 310 330 345 370 345 320 300 295 310 325

b) Radiosonde data. Radiosonde flights from Marambio and Rothera show that the 100 hPa temperature is now close to the normal. It was significantly below the normal in the second half of October.

c) Nacreous clouds were sighted at Vernadsky on July 27, 28, August 6, 10 ,13, 15, 28, 29 and September 4.

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 give 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. BAS have made ozone hole movies from TOMS images, which are on our web page and are regularly updated.

A low ozone event with central values below 200 DU occurred on the edge of the sunlit polar vortex between June 15 and June 28. The hole developed and reached over 25 million square kilometres in mid September, but is now shrinking and filling. The area remains significantly larger than that of last year and by early November was still around 18 million square kilometres. The hole is past its deepest, and minimum values are now above 125 DU. The edge of the ozone hole passed over the tip of South America, the Falklands and South Georgia during the period from October 15 to 26.

NOAA analyses show that the 50 hPa temperature was generally below the normal since early July and that in some parts of Antarctica conditions are still suitable for Type I PSC formation.

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. The email ozone bulletins will only be issued occasionally 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.