BAS Ozone Bulletin 11/99


The 1999 ozone hole filled rapidly in early December, however a remnant area over central Antarctica, with ozone values below 270 DU, persisted until early February. The transition to winter circulation is now taking place, with ozone amounts around Antarctica increasing. Total ozone values at Halley just reached 300 DU in mid January and remained 10 - 15% below the normal, with a slow decline from 280 DU in January to 250 DU in early April. Stratospheric temperatures at Halley remained below the normal until early April.

 

Note: Bulletin 10 was only posted on the www page (http://www.antarctica.ac.uk/met/jds/ozone), and then only in draft form. The final 1999 bulletin will be issued in late May.


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

 

  1.  
  2. Ozone. Mean total ozone values at Halley fell from around 220 DU in late August (25% depletion) to around 150 DU in mid September. Daily values rose briefly to reach 200 DU on September 23rd 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 had dropped below 120 DU by October 1st (60% depletion). Values rose slowly to around 180 DU in early December, with a brief rise above 200 DU around November 19. The main springtime rise in ozone values occurred in mid December, when values rose rapidly to reach 300 DU, but the transition to summer values wasn't completed until mid January. A decline to a minimum of around 240 DU in early February then set in, but values rose back to 260 DU by the end of the month. In the second half of March two periods with ozone values approaching 220 DU occurred. Throughout 2000, ozone values have been around 15% below the normal, with 25% depletion occurring during the two events in March.


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


1999 August 21 - 2000 April 6

0 0 0 0 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

151 149 153 134 126 129 137 150 147 155 145

153 160 152 158 167 167 160 162 151 152

155 159 166 166 157 166 185 206 217 216

198 181 183 187 176 174 168 165 167 174

183 167 178 195 185 192 207 219 253 261

285 284 289 296 299 313 305 289 262 244

239 240 242 287 290 270 244 291 287 290 292

281 277 286 280 274 287 283 286 282 289

293 309 296 292 285 302 303 297 281 300

277 275 267 263 253 273 265 262 274 260 259

267 259 255 245 232 238 253 251 258 242

241 253 262 265 253 279 250 282 263 267

269 272 263 279 260 245 249 265 262

259 247 258 257 264 260 267 273 265 249

265 265 257 230 240 228 222 233 229 258

260 276 253 253 247 250 223 230 229 230 259

252 250 248 254 265 260


Halley provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
1999/00 205 172 143 172 254 281 258 250
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.

  1.  
  2. Radiosonde data. The mean 100 hPa temperature rose slowly from the normal winter values of around -81 deg C in August and September to reach -70 deg C in late November (25 deg C below the normal for the time of year). Historically the spring warming took place before the end of November and the delayed break-down of the present day vortex gives rise to this large anomaly. The temperature rose rapidly to reach to -45 deg C in mid December, but then dropped back to -55 deg C. The final rise to summer values began just before Christmas and peaked in mid January at -40 deg C, which is the normal for the time of year. A significant minimum, 8 degrees below the normal, occurred in early February and it remained a few degrees below the normal until early April.

  • Stratospheric clouds, which are instrumental in the mechanism of ozone depletion, were observed from the station on July 19, August 13, 14, 15, 18 and September 1, 2, 3, 4, 10, 13, 15, 27, 28, 30.
    •



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

     

    1.  
    2. 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 generally show a 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 had dropped back to minimum levels by October 16. A second rise began on November 2, peaking at 320 DU on November 5. Values oscillated around 230 DU, with an amplitude of 60 DU, in response to short period planetary wave activity until early December when a rapid rise to above 300 DU occurred. A slow decline commenced, which produced minimum values of around 250 DU at the end of March. A significant rise, with values above 300 DU occurred in early April.

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


      1999 July 1 - 2000 April 10


      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

      155 151 145 136 126 110 124 124 145 155

      151 148 138 0 166 178 172 156 154 164 207

      227 204 254 313 320 276 259 236 165 0

      188 187 172 193 217 242 282 288 231 191

      190 250 289 282 217 162 164 173 220 262

      257 198 168 178 240 302 319 322 326 329

      327 324 315 313 302 0 0 0 264 287

      306 302 310 309 292 296 306 302 299 308 304

      285 275 285 298 305 306 304 302 301 303 257 250 255 265 272 278 275 274 268 266 273 289 294 289 291 289 278 0 289 275 278 276 286 274 269 273 276 270 262 259 255 253 254 243 0 0 0 0 0 0 0

      0 0 0 0 0 0 0 253

      265 278 282 271 275 284 286 286 280 282

      282 269 257 263 236 247 267 265 264 256

      256 0 0 275 275 284 259 235 227 242 231

      246 280 285 306 303 284 325 320 320 298


      Rothera provisional monthly mean total ozone (DU)


      Period Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
      1999/00 274 243 157 175 229 289 282 265 265
      1998/99 288 239 159 166 252 264 270 279 267 277 300 287
      1997/98 270 280 267 263

    4. 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.  
    2. 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 7th, but then fell back to 140 DU by mid month (60% depletion). A second major rise began in late October and values were oscillating around 290 DU, with an amplitude of 50 DU, in response to short period planetary wave activity until early December. Values rose rapidly to above 320 DU in mid December and then slowly declined until late March when mean values were around 260 DU. Throughout this period mean daily values were 10 - 15% below the normal for the time of year. The monthly mean of 262 DU in March is the lowest March mean for the station. In early April ozone values rose rapidly to around 310 DU which is the normal for the time of year. This was the first time throughout the 1999 - 2000 season that they had reached the normal.

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


      1999 August 1 - 2000 April 5


      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

      181 180 187 165 178 194 219 206 197 232 229

      281 259 261 334 347 308 323 334 252 259

      224 275 281 259 328 329 343 347 274 229

      206 273 334 343 309 189 213 206 252 307

      335 252 209 172 195 289 321 328 331 325

      320 315 312 331 311 315 294 284 279 282

      298 304 321 317 303 308 317 312 299 312 304

      293 310 285 294 286 306 308 316 311 310

      292 272 261 281 276 286 293 294 293 276

      281 315 311 279 313 292 290 284 292 286 280

      287 279 271 285 296 302 297 283 276 263

      269 293 282 277 257 272 261 283 279 294

      290 265 252 266 243 218 232 242 259

      285 287 266 262 283 278 287 284 287 260

      258 268 275 251 233 267 254 241 254 262

      268 250 270 278 288 268 239 235 243 221 217

      296 310 291 320 283


      Vernadsky provisional monthly mean total ozone (DU)


      Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
      1999/00 249 189 202 283 297 292 271 262
      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

    4. Radiosonde data. Radiosonde flights at Marambio and Rothera showed that the 100 hPa temperature generally remained below -70 deg C until late October. Values from occasional flights at Marambio in November are generally 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 formation of the ozone hole during August and September and its rapid filling in early December. The margins of the hole briefly crossed the southernmost tip of South America and the Falkland Islands over November 21 to 22. A remnant area over central Antarctica, with ozone values below 270 DU, persisted from late December into early February. The transition to winter circulation is now occurring. A broad collar with ozone values generally above 300 DU surrounds Antarctica, but there are small areas with values below 250 DU in south temperate latitudes. NOAA analyses show that the 50 hPa temperature is dropping in the unlit area of the polar cap, but is generally close to the normal.

     

    An interesting low ozone event in the Northern Hemisphere occurred around November 30th. Nacreous clouds were widely seen over Scotland and very low ozone values measured over the North Sea. These events were associated with unusually low stratospheric temperatures, with chemical depletion playing a minor part in the low ozone values. A further display of nacreous clouds was seen over the UK on January 29. NOAA analyses show that the Arctic 50 hPa temperature was below the normal from early December, reaching an extreme of -75 deg C in early January. Since then it has been rising, though remaining below the normal. Locally, conditions have been suitable for Type I PSC formation since mid December. At higher levels the temperature is close to the normal. Results from the THESEO 2000/SOLVE campaign show that local ozone losses of over 60% occurred near 18km in March, with total column depletions of 15 - 30%.



    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.antarctica.ac.uk/met/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. If you use or pass on data in this bulletin please make acknowledgement to J D Shanklin, British Antarctic Survey.