British Antarctic Survey Ozone Bulletin 06/96 issued 1996 October 7 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. 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 120 DU in early October (initially a little lower than in 1995, but now similar). The rate of decline has slowed and day to day variation is around 20 DU. Data from our long term record for the station indicate normal values of around 300 DU for the week beginning September 30 (with a range of 260 DU to 340 DU). Halley preliminary mean daily total ozone, (DU) Dobson No 103: Instrument constants revised 1996 March 8. (0 indicates no data) 1996 August 1 - 1996 October 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 183 184 180 177 173 174 202 179 178 179 202 170 158 177 197 167 162 165 145 140 118 126 131 173 145 128 126 126 130 127 140 133 141 128 124 142 144 126 115 113 109 Halley provisional monthly mean total ozone (DU) Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1996/97 178 152 1995/96 219 160 129 163 253 263 248 247 224 210 1957-72 295 285 300 355 350 320 300 295 285 310 The September monthly mean equals the lowest 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 September from winter values of -83 deg C to reach -78 deg C late in the month (close to the long term mean) but have since fallen to -84 deg C. 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 160 DU in mid September. 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. In late September and early October values have generally been higher, around 230 DU, with day to day variation of around 50 DU. Data from BAS long term records for the station indicate normal values of around 350 DU for the week beginning September 30 (with a range of 280 DU to 480 DU). Vernadsky preliminary mean daily total ozone (DU). Dobson No 31: Instrument constants revised 1995 December 14 1996 August 1 - 1996 October 3 (Data from September 13 - 19 are missing due to communication problems) 217 206 172 141 178 207 161 177 200 221 214 218 213 229 211 227 230 225 212 225 227 235 223 251 221 197 184 177 179 217 198 223 245 212 181 176 167 174 164 139 168 172 156 0 0 0 0 0 0 0 185 239 245 300 296 246 252 168 203 287 247 220 185 190 Vernadsky provisional monthly mean total ozone (DU) Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1996/7 206 1995/6 237 194 251 228 298 285 287 278 266 258 1957-72 310 330 345 370 345 320 300 295 310 325 The August monthly mean of 206 DU is the lowest for that month by a substantial margin, the previous lowest was 236 DU in 1992. 3 Information from other sources. TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center show that intermittent ozone reduction events occurred during the first half of August, with depletion becoming more systematic in the second half. Two of the reduction events occurred over the Antarctic Peninsula around August 4th and 8th and are associated with the very low ozone readings made at Vernadsky. The ozone "hole" now covers most of the Antarctic continent but is centred some 5 degrees from the south pole, offset towards the South Atlantic. The hole rotates with a a period of about a month and its shape changes as planetary waves interact; the most recent images show it as triangular. The fringes of the hole touched the tip of South America and the Falkland Islands around September 27th. The circumpolar high ozone belt is located at about 50 deg south. NASA's Earth Probe and ADEOS TOMS images give more detailed resolution and show an increasingly large area at the centre of the ozone hole with values less than 125 DU. UK Met Office analyses of the 100 hPa temperature field show that the area with a temperature below -80 deg C remains elongate, lying from approximately 80 deg south, 160 west to 65 deg south, 10 deg east and is centred at about 80 deg south, 20 deg west. The 100 hPa temperature at the centre of the vortex has fallen below -84 deg C. If you use or pass on this data please make acknowledgement to J D Shanklin, British Antarctic Survey. Regards, Jon Shanklin