BAS Ozone Bulletin 04/99 issued 1999 October 20

The 1999 ozone hole still covers most of Antarctica but total ozone values are now rising. The outer margins of the hole currently form a rough ellipse aligned towards the Indian Ocean. There are high ozone values over Wilkes Land. Total ozone values at Vernadsky briefly rose above 300 DU on October 7, before dropping back to 140 DU in mid October. Total ozone values at Halley are 50% below the normal for the time of year, but are slowly rising and have reached 150 DU. Stratospheric temperatures 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 values dropped below 130 DU at the end of the month; this is over 55% below the normal for the time of year. Values have risen in October and are now around 150 DU, 50% below the normal.

Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1999 September 17.
(0 indicates no data)

1999 August 21 - 1999 October 14
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

142 141 140 150

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, though it remains near -80 deg C, which is seven deg C below the normal for the time of year.

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.


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


1999 July 1 - 1999 October 19


270 277 293 278 293 324 304 294 301 311

298 294 294 293 298 273 247 219 0 211

231 276 279 277 243 224 238 244 265 273 283

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

155 151 145 136 126 110 124 124 136


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 185 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).


Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1999 May 10


1999 August 1 - 1999 October 17


291 314 270 270 277 283 257 248 249 260

224 210 225 263 253 259 214 229 227 221

221 239 221 231 235 202 211 226 256 231 249

214 187 174 181 169 232 220 191 167 178

196 191 169 178 228 194 168 218 203 177

195 210 176 237 156 168 154 139 141 135

141 178 203 245 161 244 304 297 264 275

191 191 182 172 158 140 141


Vernadsky provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1999/00 244 185
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 is generally remaining 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 and its decline. The outer margins currently form a rough ellipse aligned towards the Indian Ocean. Lowest values, below 125 DU, cover a small area close to the pole. 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.

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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