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 virtually disappeared during the past week. However, compared over the past decade, the PSC area during the past three months has been unusually large, particularly during the month of October. The vortex in early November has an area of more than 30 million square km (km2) and remains somewhat circular, still covering the Antarctic continent. The year to year natural variations in the meteorological conditions within and around the Antarctic vortex contribute considerably to the changes in size, depth and persistence of the ozone hole.

3. Observed ozone changes: As expected, ground-based and satellite column ozone measurements during late October and early November have shown a gradual increase in ozone from the lowest values earlier in October, but they still generally remain 40-60% below pre-ozone hole norms over much of the continent. The excursion of low ozone values over the southern tip of South America reported in the last Bulletin was brief, with normal ozone amounts currently being reported from Ushuaia and Comodoro Rivadavia, Argentina. Nevertheless, the zonal average ozone reported by satellite shows that mid and high latitude values during the month of October were among the lowest on record. Ozone measurements made from balloons flown from the Antarctic continent during October and early November show that the stratospheric ozone layer that was severely depleted during the past two months is beginning to recover. This appears to be due to mixing of ozone rich air from further north that is beginning to fill in the hole, and can be seen as layers with higher ozone interspersed within the highly depleted layers. This has been observed from Marambio, Neumayer and Syowa stations all located on the edge of the continent. Two stations deep within Antarctica, Belgrano, and South Pole, show some ozone recovery from October lows, but still measure more than 90% of the ozone destroyed throughout a 5 km layer in late October and early November.

4. Ozone hole characteristics: The area of the ozone hole has decreased to about 13 million km2, 50% of its peak area 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. The ozone mass deficit, a measure of the depth of the ozone hole, has decreased by about 20% from its maximum value of 54 Mt that was reached in September and again in October. This also confirms that the ozone recovery period has begun. The ozone hole last year was reported as the largest on record and its ozone mass deficit briefly peaked above all previous years, but its recovery period was well underway by mid-October and it dissipated early. This year the ozone hole also has been large and deep when compared to previous years, and there is still no indication that it will dissipate early.

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 6/2001