BAS Ozone Bulletin 06/98 issued 1998 November 13


Total ozone values rose at Halley and Vernadsky at the end of October, in a spring warming event caused by the ozone hole rotating, but have since declined again. Core values remain below 160 DU. I depart for the Antarctic next week for several months. The next bulletin will be issued when I return, unless data from Halley require urgent dissemination.


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


a) Ozone. Mean total ozone values declined from around 260 DU in early August to a minimum of 120 DU in early October at a rate of around 3 DU per day. They rose to reach 200 DU in late October, but then fell back to 150 DU. Values are well below the long-term mean, with depletion near 60%. Day to day variation remains around 25 DU.


Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1998 November 13.
Further minor revision will be required once more calibration data is available (0 indicates no data)


1998 August 1 - 1998 November 11

 0 0 238 232 232 0 0 0 0 225

0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 244 216 240 178 184

177 180 191 186 192 217 225 223 197 195

158 157 165 141 148 188 199 174 145 122

126 142 146 117 119 110 105 143 136 125

119 112 124 109 111 111 109 118 125 130

127 121 119 117 127 142 143 150 149 145

134 129 129 136 139 162 219 183 183 211 212

209 213 173 187 189 166 157 154 138 147

152 175


Halley provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1998/99 221 162 140
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 or use of moonlight. 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 rose significantly in late October, reaching -71 deg C, and then fell back to around -75 deg C, which is 18 degrees below the long term mean. This is just below the PSC threshold. Stratospheric clouds, which are instrumental in the mechanism of ozone depletion, were observed from the station on May 27, June 18, 19, 20, 21, 22, 23, 25, 26, 29, July 18, 23, 26, 27, 28, 29, 30, August 9, 27, 31, September 1 and October 19. The displays in July 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 and do not show such pronounced wave activity. Very low values were recorded several times between mid September and mid October.

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


1998 July 1 - 1998 November 10


 277 284 301 288 300 303 0 0 286 284

241 277 293 308 294 281 294 307 299 282

285 297 276 290 298 282 278 280 0 0 289

284 274 282 213 221 246 305 312 261 236

264 248 233 211 247 241 240 269 259 232

0 0 204 184 190 201 237 208 229 204 202

222 210 202 183 206 189 175 188 172 154

165 151 166 142 118 105 105 0 134 122

152 162 138 142 150 127 181 204 128 115

107 115 131 146 140 162 182 152 123 126

121 0 0 167 168 146 134 118 111 102

102 114 151 251 258 268 245 233 244 252 239

231 236 0 271 250 168 170 198 186 152


Note: The instrument calibration is in error by around 15% at 100 DU, reading too low.


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 13, 30, July 2, 3, 4, 8, August 15, September 16, 17, 18.


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 280 DU in late July to 190 DU in early September. Strong long period wave activity with a period of about a month gave a variation of around 25 DU on this value until late October when a major warming event occurred and values rose above 320 DU. Values dropped again, to around 240 DU in early November, as the vortex rotated and the day to day variation is currently around 50 DU. Values are about 35% below the long term mean, and comparable to the past few years.


Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1998 October 12


1998 August 1 - 1998 November 11


 275 269 284 252 223 255 288 296 270 237

233 232 224 210 223 250 218 257 250 242

229 199 227 195 196 206 262 223 260 241 207

251 238 258 210 219 196 182 198 182 185

195 181 197 180 143 130 153 146 237 161

183 289 210 232 218 163 210 236 184 152

135 154 145 174 176 193 245 255 157 159

147 173 203 241 242 208 225 163 152 130

132 133 160 254 296 313 341 330 335 347 334

312 305 297 337 322 234 217 251 246 181

281


Vernadsky provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1998/99 240 197 215
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

b) Radiosonde flights at Bellingshausen and Marambio show that 100 hPa temperatures rose rapidly after October 24 to near normal, and then dropped back again in early November. They are now close to normal. Anomalously low 100 hPa temperatures were recorded at Marambio on September 18. Stratospheric clouds were seen from Vernadsky on June 13 and July 14


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 slow decline of the ozone hole. It is currently near circular and centred some 15 degrees away from the pole towards Africa, covering an area comparable to that of the continent. Central values are below 160 DU. Much of the Antarctic Peninsula, Marie Byrd Land and George V Land are currently outside the ozone hole. The edge of the ozone hole crossed over the tip of South America around September 7, 18, October 1, 11 and November 10 and the area was more severely affected between October 19 and 23. The hole covered an area of around 27 million square kilometres at its largest, which is larger than in recent years.

 

The 50 hPa temperatures are now above the stratospheric cloud threshold and the spring warming is in progress. UK Met Office analyses still show core 100 hPa temperatures below -80 deg C, much lower than in recent years.



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.

 

Jon Shanklin