British Antarctic Survey Ozone Bulletin 11/96 issued 1997 January 10 This bulletin presents total column ozone measurements made using Dobson ozone spectrophotometers. Note that all ozone values are preliminary and are subject to revision from time to time when the instrument constants are re-evaluated. All ozone data is reduced to the Bass-Paur scale as recommended by the WMO. This weeks summary: I have returned from Rothera station, Antarctica, but have not yet collated all data that has been collected whilst I’ve been away. A further bulletin will be issued in late January and a final one in early May. The final spring warming has now taken place, though stratospheric temperatures did not reach the summer maximum until late December. Total ozone values are still a little below the long term mean for the time of year. Whilst in the Antarctic I experienced the effects of the enhanced uv associated with the ozone hole at first hand on November 22nd 1. Data from the British Antarctic Survey (BAS) Halley station (76 deg south, 26 deg west, on the Brunt ice shelf). a) Ozone. Routine ozone measurements from Halley station do not start until towards the end of August because the sun is not high enough to permit measurements. Mean total ozone values fell from an estimated 260 DU in early July to around 130 DU in mid September and then declined more slowly to reach 120 DU in early October. They climbed to around 180 DU by late October, but remained at that level throughout November. The lowest mean daily value seen (104 DU on October 8) is comparable to that of the previous few years. Note that contrary to reports in WMO bulletins this is not the lowest value ever recorded at Halley. Halley preliminary mean daily total ozone, (DU) Dobson No 103: Instrument constants revised 1996 October 11. (0 indicates no data) 1996 August 1 - 1996 November 28 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 164 169 168 165 163 164 192 169 168 169 194 159 150 173 193 167 154 158 138 131 118 118 126 173 145 122 126 126 124 122 140 133 141 122 119 137 144 126 115 110 109 107 123 104 134 129 113 109 118 117 115 117 119 114 139 182 200 156 136 131 143 208 183 180 199 190 153 152 150 162 169 176 211 178 149 148 145 156 160 168 145 189 222 164 157 161 163 170 185 195 195 175 177 168 176 Halley provisional monthly mean total ozone (DU) Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1996/97 166 147 139 170 1995/96 219 160 129 163 253 263 248 247 224 210 1957-72 295 285 300 355 350 320 300 295 285 310 Observations suggest that the instrument constants require further revision for measurements made when the sun is at low altitude. The September monthly mean is the lowest recorded for the month. b) Radiosonde data. Stratospheric temperatures at 100 hPa, near the peak of the ozone layer can be used to reflect changes in ozone amount. Stratospheric clouds, which are crucial to the mechanism of ozone depletion, are likely to be present when the 100 hPa temperature is below -80 deg C and may persist whilst the temperature is below -75 deg C. Data from Halley show that the 100 hPa temperature rose during October from -83 deg C to reach -73 deg C at the end of the month, which is about 8 C deg below the long term mean. The temperature increased slowly through November to reach -70 deg C (some 25 deg C below the long term mean) and the final warming began in early December. The temperature at 100 hPa remained substantially below the long term mean until it peaked at -38 deg C on the 27th. It is now around -42 deg C, about 2 deg C below the long term mean. 2. Data from the Ukrainian Antarctic Research Centre Vernadsky station (65 south, 64 west on the coast of the Antarctic Peninsula, formerly the BAS Faraday station). Routine ozone measurements commence at Vernadsky in early August, but some observations, of lower accuracy, are made in July. Mean total ozone values fell from an estimated 290 DU in early July to 190 DU in early August. The total ozone fell to exceptionally low values, below 140 DU, on August 4th and low values were also recorded around the 7th and 28th. The previous minimum mean daily value recorded during August was 170 DU in 1992. Long period planetary wave activity gave total ozone peaks of around 240 DU in mid August and late September and troughs of around 160 DU in mid September and 210 DU in mid October. Since late September short period planetary waves have been active and day to day variation was around 100 DU until early November when it dropped to around 20 DU. Mean ozone levels rose to around 380 DU in early November, but then dropped to ozone hole levels around 200 DU for the remainder of the month and into December. The final rise started around December 8th and values are now at summer levels, though around 10% down on the long term mean. Vernadsky preliminary mean daily total ozone (DU). Dobson No 31: Instrument constants revised 1996 October 28 1996 August 1 - 1997 January 3 222 211 177 149 185 213 172 188 210 231 226 230 223 241 221 237 240 235 223 236 236 243 232 256 225 204 191 186 185 224 206 229 250 219 190 185 176 182 172 147 176 181 164 154 179 179 158 137 170 178 191 222 190 196 165 175 184 225 279 207 200 247 323 305 285 208 196 160 166 326 346 359 368 217 232 358 353 337 346 344 350 261 285 323 374 381 373 280 246 209 196 179 185 195 178 185 179 179 190 223 232 208 205 189 181 180 176 180 190 204 216 222 226 199 179 202 215 228 233 246 301 305 311 310 327 299 269 256 251 253 263 269 276 288 282 278 280 284 295 310 300 316 313 303 322 310 Vernadsky provisional monthly mean total ozone (DU) Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1996/7 215 203 262 225 270 1995/6 237 194 251 228 298 285 287 278 266 258 1957-72 310 330 345 370 345 320 300 295 310 325 Observations suggest that the instrument constants may still require some further revision. The August monthly mean of 211 DU is the lowest for that month by a substantial margin, the previous lowest was 236 DU in 1992. The November monthly mean is the lowest for that month, though it is comparable to the value over the past few years. The December minimum value of 179 DU is the lowest on record for the month; the previous minimum was recorded in 1990 which had a comparable monthly mean to 1996. 3 Information from other sources was not available at Rothera. A quick look at TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center shows that the 1996 ozone hole is now over. If you use or pass on this data please make acknowledgment to J D Shanklin, British Antarctic Survey. Regards, Jon Shanklin