BAS Ozone Bulletin 01/00


The 2000 ozone hole has shrunk a little, but still covers around 24 million square kilometres. At its largest it reached 28.4 million square kilometres in early September and was the largest ever recorded ozone hole. It also formed unusually early, and it is normally late September before it reaches its maximum extent. Minimum ozone values are usually measured at the end of September or early in October. Ozone values are below 200 DU over much of the continent, with large areas showing below 125 DU and a few places below 100 DU. A broad collar of ozone rich air surrounds Antarctica, with highest values (above 450 DU) over the Davis Sea. Ozone measurements at the BAS Halley station show that ozone values are dropping rapidly and are now around 120 DU (40% of the normal value). Measurements from the BAS Rothera station show a decline from around 300 DU in early June to 115 DU in early September, with variation on a variety of time scales superimposed upon this. The decline was rapid from late August until mid September, but has now bottomed out, with recent values at around 110 DU. Ozone measurements at the Ukrainian Vernadsky station (formerly the BAS Faraday station) show that ozone values dropped from around 250 DU at the beginning of August to around 200 DU, but then briefly recovered to near normal values at the end of the month. They have now dropped to around 140 DU (40% of the normal value). The temperature at 100 hPa, near the centre of the ozone layer, is near -80°C over much of the continent and the Antarctic stratosphere is still cold enough for Type I stratospheric clouds to form and persist. The coldest area is centred over the Filchner Ice Shelf. Stratospheric clouds have been sighted from Vernadsky, Rothera and Halley. A mini ozone hole, with central values below 200 DU, periodically formed to the east of the Antarctic Peninsula over the Weddell Sea during July. This mini ozone hole probably formed due to processing of ozone through PSCs, which were far enough north to be sunlit. The feature was particularly marked on July 10 and again on July 20.

 

Ozone values over the Arctic are normally at their lowest in September and this year is no exception as can be see from the TOMS images. Although the values are low, they are low because of stratospheric dynamics and not chemistry. The temperature in the Arctic ozone layer is above -55°C, far too warm for stratospheric clouds to form. Hence there is no chemical depletion taking place and no ozone hole above the Arctic.



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

 

  1. Ozone. Ozone measurements in the first half of August were made using moonlight and are of very low accuracy. Ozone amounts have dropped from around 200 DU at the end of August (30% depletion) to 120 DU at the end of September (60% depletion).


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


2000 August 1 - 2000 September 28

0 0 0 0 0 0 0 0 0 201

151 174 182 0 0 165 153 149 0 0

0 0 0 0 0 0 255 188 165 180 179

189 184 196 192 199 206 183 167 152 170

172 165 167 155 138 143 152 129 127 123

135 134 129 129 120 110 121 114


Halley provisional monthly mean total ozone (DU)


Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
2000/01 179
1999/00 205 172 143 172 254 281 258 250 256 221
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
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. Radiosonde data. The mean 100 hPa temperature is close to the normal winter value of around -81 deg C.

  • Stratospheric clouds, which are instrumental in the mechanism of ozone depletion, were observed from the station on July 10, 12, August 2 and 22.
    •



    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 lowest values are around 105 DU once the 15% correction is applied to the measurements given below. 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.

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


      2000 July 1 - 2000 September 27


      273 249 276 0 0 288 236 205 144 173

      225 279 264 245 225 232 243 225 201 246

      225 178 213 201 225 233 245 0 242 220 246

      232 211 228 203 228 240 231 246 246 286

      298 252 226 217 238 0 0 0 188 196

      179 175 184 220 193 232 262 287 273 258 202

      195 208 193 184 187 162 127 111 114 108

      138 128 121 115 0 0 124 111 94 92

      104 119 101 98 111 120 110


      Rothera provisional monthly mean total ozone (DU)


      Period Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
      2000/01 231 230
      1999/00 274 243 157 175 229 289 282 265 264 290 282 293
      1998/99 288 239 159 166 252 264 270 279 267 277 300 287
      1997/98 270 280 267 263

    3. 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 23, 26, July 10, August 21 and 22.

     

    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. During August mean total ozone values oscillated within 50 DU of 250 DU (25% depletion). Values briefly rose to near normal (320 DU) at the end of the month, but declined to 150 DU (55% depletion) by mid September and 140 DU (60% depletion) by the end of the month

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


      2000 August 1 - 2000 September 27


      255 245 265 236 248 263 252 246 246 286

      277 255 213 213 229 252 245 205 214 207

      198 192 204 238 196 219 258 291 316 298 242

      239 237 213 209 195 177 148 141 142 147

      164 138 130 145 141 164 160 133 119 118

      120 158 134 139 149 148 131


      Vernadsky provisional monthly mean total ozone (DU)


      Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year
      2000/01 242
      1999/00 249 189 202 283 297 292 271 262 293 260
      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
      1957-72 310 330 345 370 345 320 300 295 310 325

    3. Radiosonde data. Radiosonde flights from Marambio show that the 100 hPa temperature is generally below -70 deg C and within the range of historic variation.

      Stratospheric clouds were seen from Vernadsky on June 19, July 8, 17, 18, 21, 26, and August 4.



    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. TOVS and TOMS currently have significantly different calibrations, with TOVS reading some 50 DU higher than TOMS. TOMS values are close to ground-based values. BAS have made a 2000/2001 ozone hole movie from TOMS images, which is on our web page and will generally be updated every week. NOAA analyses show that the 50 hPa temperature has remained below the normal during the winter, though a rise to normal (-82 deg C) occurred in the second half of August. Subsequently the atmosphere cooled and conditions are still suitable for Type I PSC formation.



    Further information is available on the BAS ozone web page, which contains earlier bulletins, data, graphs and general ozone information. It is often updated several times a week. The email ozone bulletins will be issued less frequently this year so for the latest information see: 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.