World Meteorological Organization

1. The Secretariat of the World Meteorological Organization (WMO) distributes Bulletins providing current Antarctic ozone hole conditions during August-December each year. Bulletins are distributed via the WMO-Global Telecommunication System (GTS) and are also available through the Atmospheric Research and Environment Programme web page at www.wmo.ch/web/arep/ozone.html . In addition to the National Meteorological Services, the information in these Bulletins should be made available to the national bodies representing their countries with UNEP and that support or implement the Vienna Convention for the Protection of the Ozone Layer and its Montreal Protocol.

2. Meteorological conditions: The area with temperatures low enough to form polar stratospheric clouds (PSCs) in the lower stratosphere has remained high, averaging more than 15 million square kilometres (million km2) during the past few weeks. This is nearly 1/2 of the vortex area, and about 2/3 the present size of the ozone hole. Compared over the past decade, the PSC area this year is exceptionally large for mid to late October, and the vortex has been very circular, an indication of its persistent strength. However, since mid October there is some indication that the vortex is beginning to weaken, with the vortex that was centred on the pole now less circular and extended somewhat toward the southern tip of South America and the South Atlantic Ocean.

3. Observed ozone changes: Ground-based column ozone measurements during mid October have averaged 40-60% below the pre-ozone-hole norms at Arrival Heights, Belgrano, Halley, King George Island, Marambio, Mirny, Syowa and Vernadsky stations. The Argentine city of Ushuaia has remained about 20% below norms except for a brief period early this week when the ozone hole was overhead. Dumont d'Urville, and Kerguelen Island stations have also remained generally outside the ozone hole. Ozone measurements made from balloons flown from the Antarctic continent during mid October show that the stratospheric ozone below 20 km altitude has been severely depleted during the past two months, a situation similar to recent years. Two stations deep within the Antarctic continent, Belgrano, and South Pole, continue to show more than 95% of the ozone destroyed throughout a 5 km layer, while Marambio, Neumayer and Syowa stations on the edge of the continent have measured similar depletions, but with somewhat less vertical extent.

4. Ozone hole characteristics: The area of the ozone hole has decreased 10-15% after reaching its peak of 25 million km2 in mid September. In the last two Bulletins the "ozone mass deficit" was described as the mass of ozone destroyed in the Antarctic ozone hole region, expressed in millions of tons (Mt) of ozone and estimated by comparison of the daily column ozone data available from satellites and ground stations with the pre-ozone hole norms. Last year the maximum ozone deficit of 57 Mt was reached by the second week in September, the highest value on record. This deficit quickly decreased to less than 40 Mt by 1 October and remained below 30 Mt after 20 October. This year the ozone mass deficit reached its maximum of about 54 Mt both in mid September and again in mid October. The average ozone mass deficit for the month of September was 50 Mt and increased slightly during the first three weeks of October to 51 Mt. These averages are the largest on record and can be considered as a measure of the depth of the 2001ozone hole. Although the area of the ozone hole has decreased since its peak size in mid September, the ozone mass deficit has not had a corresponding decrease.

5. Acknowledgements: These Bulletins use provisional data from the WMO Global Atmosphere Watch (GAW) stations operated within or near Antarctica by: Argentina (Comodoro Rivadavia, San Julian, Sobral, Ushuaia), Argentina/Finland (Marambio), Argentina/Italy/Spain (Belgrano), Australia (Macquarie Island), France (Dumont D'Urville and Kerguelen Island), Germany (Neumayer), Japan (Syowa), New Zealand (Arrival Heights), Russia (Mirny), Ukraine (Vernadsky), UK (Halley, Rothera), Uruguay (King George Island), and USA (South Pole). Satellite ozone data are also used and provided by NASA - Total Ozone Mapping Spectrophotometer (TOMS) and by the National Oceanic and Atmospheric Administration (NOAA) - TIROS Operational Vertical Sounder (TOVS). Potential vorticity maps are provided by ECMWF and their ERA-15 and daily T106 meteorological fields are analysed by the Norwegian Institute for Air Research (NILU) Kjeller, Norway, to provide vortex extent and extreme temperature information. Ozone data analyses are prepared in collaboration with the WMO World Ozone and Ultraviolet Data Centre in Toronto, Canada through the co-operation and support of the Meteorological Service of Canada (MSC). Graphics support has been provided to WMO by NOAA Aeronomy Laboratory in Boulder, Colorado, USA. Supporting graphics can be found at http://exp-studies.tor.ec.gc.ca/cgi-bin/selectMap (MSC) and http://www.nilu.no/projects/nadir/o3hole (NILU).

Questions regarding the scientific content of this Bulletin should be addressed to

Dr. Michael Proffitt, Senior Scientific Officer of WMO: e-mail proffitt@wmo.ch

END of WMO Antarctic Ozone Bulletin 5/2001