British Antarctic Survey
The ozone hole continues to develop, with central values now below 180 DU. Ozone values in the Antarctic Peninsula and the Weddell Sea areas have declined over the past week and are now 25 - 40% below normal. The centre of the polar vortex has moved back towards the Weddell Sea area. Lower than normal ozone values are likely to be recorded over southern South America and the Falkland Islands over the next couple of days.
1. Data from the British Antarctic Survey (BAS) Halley station (76-deg south, 26-deg west, on the Brunt ice shelf).
a) Ozone. Routine ozone measurements from Halley station started towards the end of August. Prior to that, the sun was not high enough to permit measurements, however a few observations using moonlight were made. These 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%) have now commenced. These suggest that values rose to around 240 DU towards the end of August but have now fallen to 180 DU. Ozone values are comparable to those of the past few years, but well below the long-term mean, with depletion at around 35 - 40%.
Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1997 May 2.
(0 indicates no data)
1997 August 1 - 1997 September 11
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 0 221 251 210 194 187 179 192 186 186 218 218 205 191 167 178 185
Halley provisional monthly mean total ozone (DU)
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 has now returned to normal. The maximum temperature occurred a few days after the ozone peak. 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 the mean ozone values rose from around 230 DU at the beginning of August to 290 DU mid month and have since declined back to around 230 DU. Day to day variation is around 30 DU.
Rothera preliminary mean daily total ozone, (DU)
(0 indicates no data or data not available)
1997 August 1 - 1997 September 8
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
Routine ozone measurements commence at Vernadsky in early August, but some observations, of lower accuracy, are made in July. 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). Values have now fallen to around 240 DU, a depletion of around 25%. Day to day variation is around 30 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.
Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 August 15
1997 August 1 - 1997 September 6
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
Vernadsky provisional monthly mean total ozone (DU)
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 growing and deepening and remains relatively elongate. Minimum values lie below 180 DU. The normal circumpolar high ozone belt is present. UK Met Office analyses also show that the polar vortex is still elongated, centred on 77-deg south, 30-deg west, and aligned roughly 70-deg south, 20-deg east to 70-deg south, 90-deg west on September 10. The analyses and the radiosonde profiles from Halley and Neumayer show a strong warming event 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 is likely to pass over southern South America and the Falkland Islands during the next couple of days.
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.