This bulletin summarises total column ozone measurements made at British Antarctic Survey stations during 1995/96 using a Dobson ozone spectrophotometer. Further details can be found at http://www.nbs.ac.uk/public/icd/ozone_pub.
Faraday station was run by the British Antarctic Survey until 1996 February 6, when it was handed over to the Ukrainian Antarctic Research Centre and became Vernadsky station.
Preliminary mean daily ozone values dropped from values of around 280 Dobson Units (DU) at the beginning of August to around 175 DU at the end of September (50% depletion). Individual daily values dropped as low as 132 DU. The first week of October saw a major spring warming event, with a rise in mean total ozone to over 300 DU as the circumpolar high ozone belt moved across the station. Mean values then fell back to around 190 DU in mid October before rising again to over 300 DU in a second warming event at the end of October. Mean values dropped back again to 200 DU in early November before slowly rising to around 315 DU in the final warming event of the year in mid December. Values slowly declined from the December peak to around 260 DU at the end of April.
Generally values in the 95/96 season were a little above those reached in 1993 and 1994 during the first half of the season and below during the second half. The final spring warming was much later than in either year. Values were significantly below those of the long term mean throughout the season.
Faraday provisional monthly mean total ozone (DU)
Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1995/6 237 194 251 228 298 285 287 278 266 258 1957-72 310 330 345 370 345 320 300 295 310 325
Many of the monthly means are either the lowest or near the lowest on record. The yearly mean is the lowest on record.
Preliminary mean daily ozone values dropped slowly from around 240 DU at the beginning of August to around 200 DU in early September, but fell rapidly to a minimum of 120 DU at the end of September (60% depletion). The decline then halted and ozone values rose slowly, reaching around 200 DU in early December. Finally, a more rapid spring warming took place, reaching a maximum of just over 300 DU in mid December. Values slowly declined from this peak, reaching 215 DU in mid April.
The early part of the season was similar to 1993, however the final spring warming was later and reached a lower peak value. Values after the peak were lower than in 1993. Throughout the season the running mean daily values were never higher than the reference period extreme minimum.
Halley provisional monthly mean total ozone (DU)
Period Aug Sep Oct Nov Dec Jan Feb Mar Apr Year 1995/96 219 160 129 163 253 263 248 247 224 210 1957-72 295 285 300 355 350 320 300 295 285 310
Many of the monthly means are either the lowest or near the lowest on record. All the monthly means from January onwards and the yearly mean are the lowest on record.
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 -70 deg C. In the 1995/96 season the 100 hPa temperature remained at winter values (below -80 deg C), until early October. It then rose slowly, reaching -75 deg C in mid November, before rising more rapidly to peak at -40 deg C in late December. During the late summer and autumn slow cooling took place, with the temperature reaching -60 deg C by the end of April. Almost throughout the season the lower stratospheric temperature was below the long term mean. The departure is particularly marked from mid October to mid December and from mid January to mid February. The season until mid November was similar to 1993, but the spring warming was later in 1995.
TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center showed that ozone depletion intensified during September, with the ozone "hole" covering most of the Antarctic continent and centred close to the south pole. Ozone values at Halley and Faraday were a little above those of last year, because the centre of the hole was further away from the BAS stations than in 1994. During October the hole became more elongated, but changed little in total area. The hole started to fill and became much more elongated in early November, but become more circular again later in the month. The axis of elongation rotated around the Antarctic continent with a period of about a month. This rotation of the "hole" gave rise to the larger day to day variation in ozone amount seen at Faraday, which was sometimes inside and sometimes outside the ozone hole. The edge of the hole clipped the tip of South America and the Falkland Islands between October 12 and 14.
If you use or pass on this data please make acknowledgement to J D Shanklin, British Antarctic Survey.
Regards, Jon Shanklin (firstname.lastname@example.org)