British Antarctic Survey
The ozone hole continues to develop, with central values now below 150 DU. Ozone values over the Antarctic Peninsula and the Weddell Sea areas continue to decline and are now 40 - 50% below normal. The edge of the ozone hole passed over the tip of South America and the Falkland Islands on September 13 and 14.
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 150 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 45 - 50%. 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.
(0 indicates no data)
1997 August 1 - 1997 September 18
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 maximum temperature occurred a few days after the ozone peak. The temperature has now returned to near normal. 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 the mean ozone values rose from around 230 DU at the beginning of August to 290 DU mid month and have since declined to around 210 DU. Day to day variation is around 40 DU.
Rothera preliminary mean daily total ozone, (DU)
(0 indicates no data or data not available)
1997 August 1 - 1997 September 15
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 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). Values have now fallen to around 200 DU, a depletion of about 40%. Day to day variation is around 40 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.
Vernadsky preliminary mean daily total ozone (DU).
Dobson No 31: Instrument constants revised 1997 August 15
1997 August 1 - 1997 September 13
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 deepening and remains relatively elongate. Minimum values lie below 150 DU. The normal circumpolar high ozone belt is present, with a prominent high over the southern Atlantic ocean. UK Met Office analyses also show that the polar vortex is elongated, centred on 85-deg south, 0-deg west, and aligned roughly 70-deg south, 20-deg east to 70-deg south, 160-deg west on September 18. The analyses and the radiosonde profiles from Halley and Neumayer show a strong warming event 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 and 14.
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.