British Antarctic Survey Ozone Bulletin 03/96 issued 1996 September 14 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 south, 26 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. The measurements suggest that values were steady at around 180 DU until early September, (a little lower than in 1995), and are now generally starting to drop. Data from our long term record for the station indicate normal values of around 300 DU for this period (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 September 12 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 Halley provisional monthly mean total ozone (DU) Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1996/97 178 1995/96 219 160 129 163 253 263 248 247 224 210 1957-72 295 285 300 355 350 320 300 295 285 310 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 is presently close to the long term mean, at around -81 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). Preliminary ozone values from Vernadsky show mean total ozone values generally around 220 DU during August, but with exceptionally low values below 140 DU on August 4th and also with low values around the 7th and 28th. Day to day variation is around 20 DU. Data from BAS long term records for the station indicate normal values of around 330 DU for this period (with a range of 280 DU to 380 DU). The previous minimum mean daily value recorded during the month was 170 DU in 1992. The August monthly mean of 206 DU is the lowest for that month by a substantial margin, the previous lowest was 236 DU, also in 1992. Early September saw an initial rise to 270 DU followed by a rapid fall to 175 DU by September 5th. Vernadsky preliminary mean daily total ozone (DU). Dobson No 31: Instrument constants revised 1995 December 14 1996 August 1 - 1996 September 5 217 206 172 141 178 207 161 177 200 221 214 218 213 229 211 227 230 225 212 225 227 235 223 251 221 197 184 177 179 217 198 223 245 212 181 176 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 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 and is centred close to the south pole, but offset towards South America. It is slightly elongated in shape and is rotating with a period of about a month. The circumpolar high ozone belt is located at about 50 deg south. NASA's Earth Probe TOMS images give more detailed resolution and the solar elevation now allows the sensor to image the continent north of 80 deg south. These images show that the main region of ozone depletion is currently located near 70 deg south, 110 deg west. There is some evidence that the centre of the 'hole', which is not yet sunlit, has less ozone depletion than the margins. The relatively high total ozone value at Halley on September 9 may correspond to an incursion of this air over the station. UK Met Office analyses of the 100 hPa temperature field show that the area with the temperature below -80 deg C is very elongate, lying from approximately 70 deg south, 110 west to 70 deg south, 40 east and is centred at about 80 deg south. On the opposite side of the continent the spring warming has already reached the coastal fringe of Antarctica at 130 deg east where the 100 hPa temperature is just above -50 deg C. If you use or pass on this data please make acknowledgement to J D Shanklin, British Antarctic Survey. Regards, Jon Shanklin j.shanklin@bas.ac.uk British Antarctic Survey, Cambridge, England