British Antarctic Survey Ozone Bulletin 09/96 issued 1996 October 28 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: Minimum ozone levels are now passed and the ozone hole is shrinking in size and filling. The centre of the hole still has total ozone values below 150 DU, but most coastal stations are seeing regular warming events as the hole rotates. 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 are now climbing and have reached 160 DU, which is higher than at the same time in 1995, but still only half the value of the long term mean. Day to day variation has increased to around 40 DU. The lowest mean daily value seen (104 DU on October 8) is comparable to that of the previous few years. Data from our long term record for the station indicate normal values of around 310 DU for the week beginning October 21 (with a range of 260 DU to 350 DU). Halley preliminary mean daily total ozone, (DU) Dobson No 103: Instrument constants revised 1996 October 11. (0 indicates no data) 1996 August 1 - 1996 October 24 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 164 169 168 165 163 164 192 169 168 169 194 159 150 173 193 167 154 158 138 131 118 118 126 173 145 122 126 126 124 122 140 133 141 122 119 137 144 126 115 110 109 107 123 104 134 129 113 109 118 117 115 117 119 114 139 182 200 156 136 132 Halley provisional monthly mean total ozone (DU) Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1996/97 166 147 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 -74 deg C late in the month, which is about 6 C deg 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). No new data has been received this week due to communications problems. 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. 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. Day to day variation is around 60 DU. Data from BAS long term records for the station indicate normal values of around 350 DU for the week beginning October 21 (with a range of 280 DU to 450 DU). Vernadsky preliminary mean daily total ozone (DU). Dobson No 31: Instrument constants revised 1996 October 14 1996 August 1 - 1996 October 10 222 211 177 146 183 212 166 182 205 226 219 223 217 234 215 232 235 230 217 230 232 240 228 255 224 202 188 182 183 222 203 228 250 217 186 181 172 179 169 142 173 177 161 150 176 176 156 133 165 175 190 244 249 305 301 251 257 173 208 292 250 225 189 195 162 174 183 228 291 209 201 Vernadsky provisional monthly mean total ozone (DU) Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1996/7 211 203 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 will require some further revision when enough direct sun observations have been obtained. 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. 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. Depletion continued throughout September, reaching a maximum extent in early October, when the "hole" covered the entire Antarctic continent. The ozone "hole" is shrinking, but still covers much of the Antarctic continent. It is centred some 5 degrees from the south pole, offset towards the Indian Ocean. The hole is now rotating with a period of about two weeks and its shape changes as planetary waves interact; the most recent images (Oct 27) show it as very elongated, with the axis of elongation pointing towards South Africa. The fringes of the hole clipped the tip of South America around October 17th. The circumpolar high ozone belt is centred at about 60 deg south. Coastal stations such as Halley, Scott Base, Syowa and Vernadsky are seeing these higher ozone values from time to time as the hole rotates. NASA's Earth Probe and ADEOS TOMS images give more detailed resolution and show that ozone values near the centre of the ozone hole are now between 150 and 125 DU. UK Met Office analyses of the 100 hPa temperature field (to Oct 28) show that the hole is centred at about 80 deg south, 40 deg east. The region has warmed but a sizeable area at the centre of the polar vortex still has 100 hPa temperatures between -75 and -80 deg C. Particularly strong temperature gradients exist over the base of the Antarctic Peninsula and Weddell Sea and over Wilkes Land. If you use or pass on this data please make acknowledgement to J D Shanklin, British Antarctic Survey. Regards, Jon Shanklin