British Antarctic Survey
Ozone Bulletin 06/97 issued 1997 September 26



The elliptically shaped ozone hole continues to develop, with central values now below 125 DU. Ozone values over the Antarctic Peninsula increased to near normal when the ozone hole rotated away from the Peninsula, but have now dropped again. Ozone values over Weddell Sea areas continue to decline and are now 55% below normal. The edge of the ozone hole clipped the tip of South America and the Falkland Islands on September 23 and 24.



1. Data from the British Antarctic Survey (BAS) Halley station (76-deg south, 26-deg west, on the Brunt ice shelf).


a) Ozone. A few observations made using moonlight suggest that total ozone values fell from an estimated 300 DU in early July to around 200 DU in mid August. Low accuracy measurements on the zenith sky (which may need a correction of 5 - 10%) commenced in late August, when the solar elevation became high enough. These suggest that values rose to around 240 DU towards the end of August but have now fallen to 130 DU. Day to day variation is around 15 DU. Ozone values are comparable to those of the past few years, but well below the long-term mean, with depletion at around 55%. The rate of decline is also comparable to that of the past few years.


Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1997 May 2 and minor revision 1997 September 26.
(0 indicates no data)


1997 August 1 - 1997 September 25

0 0 0 0 0 0 0 0 0 0
194 0 194 195 213 214 221 215 230 217
0 0 0 0 0 0 221 251 210 194 187
179 192 186 186 218 218 205 191 170 178
184 163 167 155 176 174 141 149 165 171
161 154 137 128 127


Halley provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1997/98 211
1996/97 172 155 149 181 260 278 265 245 242 216
1995/96 219 160 129 163 253 263 248 247 224 210
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. Gif images showing the data are available on the BAS ozone web-page.

b) Radiosonde data. Stratospheric temperatures at 100 hPa, near the peak of the ozone layer, can be used to reflect changes in ozone amount. Stratospheric clouds, which are crucial to the mechanism of ozone depletion, are likely to be present when the 100 hPa temperature is below -80 deg C and may persist whilst the temperature is below -75 deg C. Data from Halley show that the mean 100 hPa temperature increased substantially towards the end of August, from close to the long term norm of -83 deg C, to -78 deg C, near the upper limit of the long term range. The temperature then returned to near normal and has now risen from around -83 deg C in mid September to around -78 deg C. Stratospheric clouds have been observed from the station on August 1, 3, 6, 7, 8, 10, 13, 14 and 15. The display on August 10 was particularly vivid.



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 that running mean ozone values rose from around 230 DU at the beginning of August to 290 DU mid month and then declined to around 210 DU by mid September. A rapid rise then pushed the running mean above 300 DU, with the daily mean reaching 359 DU on September 18. Day to day variation is currently around 80 DU.

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


1997 August 1 - 1997 September 22


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


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 have been observed from Rothera on June 8, 10, 13, 15, July 4, 17, 21, 23, and August 4.


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).


Routine ozone measurements commence at Vernadsky in early August, but some observations, of lower accuracy, are made in July. Running mean total ozone values fell from an estimated 350 DU in early July to 240 DU in early August, then rose to over 300 DU by the end of the month (close to the long term mean). The running mean fell back to around 210 DU in the first half of September, before dramatically rising to near normal (340 DU) just after mid month. Day to day variation is currently around 100 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, and on September 13th when the centre of the ozone hole passed near the station. Six days later values rose to 375 DU when the circumpolar high ozone belt was over the station.


Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 August 15


1997 August 1 - 1997 September 20


275 216 238 231 235 236 236 287 281 265
260 262 280 290 290 259 244 240 240 253
241 303 296 301 261 292 319 317 310 305 258
239 202 210 260 259 256 237 218 216 213
205 187 156 210 274 358 373 374 375 288


Vernadsky provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1997/98 268
1996/97 217 205 263 226 271 304 279 277 294 260
1995/96 237 194 251 228 298 285 287 278 266 258
1957-72 310 330 345 370 345 320 300 295 310 325


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 developing ozone hole. Intermittent ozone reduction events occurred during late July and early August. The ozone "hole" is still deepening and remains relatively elongate. Minimum values at the centre of the hole lie below 125 DU, but ozone values are relatively high over the continental edge at around 70-deg east. The normal circumpolar high ozone belt is present, with prominent highs over the southern Atlantic and Pacific oceans. UK Met Office analyses show that the elongated polar vortex is centred approximately on 87-deg south, 160-deg west, and aligned in a gentle 'S' shape roughly 60-deg south, 30-deg west to 65-deg south, 150-deg east on September 26. The analyses and the radiosonde profiles from Halley and Neumayer show that a strong warming event occurred over the Weddell Sea area at the end of August as the centre of the vortex displaced towards the Pacific. The edge of the ozone hole passed over the tip of South America and the Falkland Islands on September 13/14 and just clipped the area on September 23/24.



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.