BAS Ozone Bulletin 05/99 issued 1999 November 1

The 1999 ozone hole still covers most of Antarctica but total ozone values are slowly rising and only a few locations now have values below 150 DU. The outer margins of the hole currently form a rough ellipse offset from the pole towards the Atlantic Ocean. There are high ozone values over Wilkes Land. A brief warming event took place over Rothera and Vernadsky on October 7, but ozone values at these stations are still generally 50% below the normal for the end of October. Total ozone values at Halley are slowly varying around 140 DU, which is 55% below the normal for the end of October. Stratospheric temperatures over Antarctica remain cold enough for stratospheric clouds to exist.

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

1. Ozone. Mean total ozone values at Halley fell from around 220 DU in late August to around 150 DU in mid September, then rose briefly to reach 200 DU on September 23 ^rd when planetary wave activity brought the edge of the ozone hole close to the station. This is the highest ozone amount at the station in the last 10 days of September since 1990. The fall continued at around 2.6 DU per day, and daily values dropped below 120 DU by October 1 ^st . During October values have slowly varied around 140 DU, and are now 55% below the normal for the end of the month.

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

1999 August 21 - 1999 October 28
0 175 180 254 220 181 220

231 211 206 192 205 206 218 201 209 196

185 178 173 169 167 145 140 150 175 177

151 151 199 159 136 121 125 129 125 117

114 116 139 170 162 132 130 137 140 159

142 141 140 139 150 155 132 144 150 155

151 149 153 134 126 129 137 147

Halley provisional monthly mean total ozone (DU)

Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1999/00 205 172
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
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.

2. Radiosonde data. Data from Halley show that the mean 100 hPa temperature is slowly rising, and had reached -77 deg C (13 deg C below the normal for the time of year) at the end of October.

2. Data from the British Antarctic Survey (BAS) Rothera station (68-deg south, 68-deg west on Adelaide Island).

1. 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 mean daily total ozone values show a generally 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. Mean total ozone values dropped from 290 DU at the beginning of August to 115 DU in late September, a rate of decline of 2.9 DU per day. A brief rise took values up to 290 DU on October 7, but they dropped back to minimum levels by October 16 and are beginning to rise slowly.


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


1999 July 1 - 1999 October 23


299 313 281 270 267 290 0 258 260 260

210 228 239 256 249 243 200 232 262 239

225 222 219 224 241 214 210 210 225 219 223

186 175 0 165 164 194 183 162 158 164

154 143 162 160 184 149 148 163 162 162

159 173 161 166 130 129 119 116 114 0

150 175 192 207 157 274 292 280 279 239

155 151 145 136 126 110 124 124 145 155

151 148 138


Rothera provisional monthly mean total ozone (DU)


Period Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
1999/00 274 243 157
1998/99 288 239 159 166 252 264 270 279 267 277 300 287
1997/98 270 280 267 263


2. 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 6, 7, 9, 10, 12, 29, July 12, 13, August 22 and 31.

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).

1. Ozone. Running mean total ozone values fell from around 290 DU in late July (10% depletion) to 160 DU in late September (55% depletion), giving a rate of decline of around 2.2 DU per day. The September mean of 189 DU is the lowest recorded September mean for the station. Daily values rose from the beginning of October to reach over 300 DU on the 7 ^th , but then fell back to 140 DU by mid month (60% depletion), before rising slowly. They are currently around 50% below the normal for the end of October.


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


1999 August 1 - 1999 October 27


296 319 275 275 282 288 262 253 254 265

229 215 230 268 258 264 219 234 232 226

226 244 226 236 240 206 215 231 261 235 252

219 191 177 186 174 237 224 194 170 182

201 196 174 183 233 199 171 222 208 181

199 215 181 242 161 173 159 142 146 138

145 183 208 250 164 249 309 301 269 280

196 195 187 177 163 145 145 152 182 204

181 180 187 165 178 194 219


Vernadsky provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1999/00 249 189
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
1995/96 240 199 252 230 296 284 285 276 264 258
1957-72 310 330 345 370 345 320 300 295 310 325


2. Radiosonde data. Radiosonde flights at Marambio and Rothera show that the 100 hPa temperature generally remains below -70 deg C, which is a few degrees below the normal for the time of year, but within the range of historic variation.
   
   Stratospheric clouds were seen from Vernadsky on July 31.

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 progressive development of the ozone hole, which is now slowly filling. The outer margins currently form a rough ellipse offset from the pole towards the Atlantic Ocean. Lowest values, below 150 DU, cover small areas close to the pole and over the Weddell Sea. There are high values over Wilkes Land, which is outside the polar vortex. UK Met Office charts show that the 100 hPa temperature remains below -75 deg C over much of Antarctica, and no areas are below -80 deg c.

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 are reduced to the Bass-Paur scale as recommended by the WMO. The reference period used for the normals is 1957 - 1972. IfyouuseorpassondatainthisbulletinpleasemakeacknowledgementtoJDShanklin, BritishAntarcticSurvey.

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