British Antarctic Survey
The elliptically shaped ozone hole continues to develop, with central values now below 125 DU. Ozone values over the Antarctic Peninsula increased to near normal when the ozone hole rotated away from the Peninsula, but have now dropped again. Ozone values over Weddell Sea areas continue to decline and are now 55% below normal. The edge of the ozone hole clipped the tip of South America and the Falkland Islands on September 23 and 24.
1. Data from the British Antarctic Survey (BAS) Halley station (76-deg south, 26-deg west, on the Brunt ice shelf).
a) Ozone. A few observations made using moonlight suggest that total ozone values fell from an estimated 300 DU in early July to around 200 DU in mid August. Low accuracy measurements on the zenith sky (which may need a correction of 5 - 10%) commenced in late August, when the solar elevation became high enough. These suggest that values rose to around 240 DU towards the end of August but have now fallen to 130 DU. Day to day variation is around 15 DU. Ozone values are comparable to those of the past few years, but well below the long-term mean, with depletion at around 55%. The rate of decline is also comparable to that of the past few years.
Halley preliminary mean daily total ozone, (DU)
Dobson No 103: Instrument constants revised 1997 May 2 and minor revision 1997 September 26.
(0 indicates no data)
1997 August 1 - 1997 September 25
Halley provisional monthly mean total ozone (DU)
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 mean 100 hPa temperature increased substantially towards the end of August, from close to the long term norm of -83 deg C, to -78 deg C, near the upper limit of the long term range. The temperature then returned to near normal and has now risen from around -83 deg C in mid September to around -78 deg C. Stratospheric clouds have been observed from the station on August 1, 3, 6, 7, 8, 10, 13, 14 and 15. The display on August 10 was particularly vivid.
Data from the British Antarctic Survey (BAS) Rothera station (68-deg south, 68-deg west on Adelaide Island).
a) Ozone. Ozone measurements from Rothera are made using a SAOZ (Systeme d'Automatique Observations Zenithales) spectrometer. This is a research instrument, but the daily ozone values are available. These show that running mean ozone values rose from around 230 DU at the beginning of August to 290 DU mid month and then declined to around 210 DU by mid September. A rapid rise then pushed the running mean above 300 DU, with the daily mean reaching 359 DU on September 18. Day to day variation is currently around 80 DU.
Rothera preliminary mean daily total ozone, (DU)
(0 indicates no data or data not available)
1997 August 1 - 1997 September 22
Routine ozone measurements commence at Vernadsky in early August, but some observations, of lower accuracy, are made in July. Running mean total ozone values fell from an estimated 350 DU in early July to 240 DU in early August, then rose to over 300 DU by the end of the month (close to the long term mean). The running mean fell back to around 210 DU in the first half of September, before dramatically rising to near normal (340 DU) just after mid month. Day to day variation is currently around 100 DU. Particularly low values were recorded on August 2nd, when the station was affected by one of the ozone reduction events associated with the forming ozone hole, and on September 13th when the centre of the ozone hole passed near the station. Six days later values rose to 375 DU when the circumpolar high ozone belt was over the station.
Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 August 15
1997 August 1 - 1997 September 20
Vernadsky provisional monthly mean total ozone (DU)
TOVS satellite images from the US NCEP/NWS/NOAA Climate Prediction Center and EP/TOMS images from the US NASA/GSFC show the developing ozone hole. Intermittent ozone reduction events occurred during late July and early August. The ozone "hole" is still deepening and remains relatively elongate. Minimum values at the centre of the hole lie below 125 DU, but ozone values are relatively high over the continental edge at around 70-deg east. The normal circumpolar high ozone belt is present, with prominent highs over the southern Atlantic and Pacific oceans. UK Met Office analyses show that the elongated polar vortex is centred approximately on 87-deg south, 160-deg west, and aligned in a gentle 'S' shape roughly 60-deg south, 30-deg west to 65-deg south, 150-deg east on September 26. The analyses and the radiosonde profiles from Halley and Neumayer show that a strong warming event occurred over the Weddell Sea area at the end of August as the centre of the vortex displaced towards the Pacific. The edge of the ozone hole passed over the tip of South America and the Falkland Islands on September 13/14 and just clipped the area on September 23/24.
Further information is available on the BAS ozone web page, which contains earlier bulletins, data, graphs and general ozone information. The url is:
http://www.nbs.ac.uk/public/icd/jds/ozone
Note that all ozone values in this bulletin are preliminary and are subject to revision from time to time when the instrument constants are re-evaluated. Final data will be archived with WOUDC, Toronto in due course, but preliminary data back to 1973 are available from BAS on request. All Dobson ozone data is reduced to the Bass-Paur scale as recommended by the WMO. If you use or pass on this data please make acknowledgement to J D Shanklin, British Antarctic Survey.