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: Although the temperatures low enough to form polar stratospheric clouds (PSCs) are no longer present, the polar vortex remains strong and exceptionally large (near 30 million square km), rather circular, and still covering the Antarctic continent. Such a strong persistent vortex is uncommon, although not without precedent. Meteorological conditions, such as the size and strength of the vortex, strongly influence the size, depth and persistence of the Antarctic ozone hole.

3. Observed ozone changes: Ground-based and satellite column ozone measurements during mid-November have continued to show a gradual increase in ozone from the minimum values reported early in October, although column ozone still generally remains more than 35% below pre-ozone hole norms over most of the Antarctic continent. In all previous years, the area with more than 50% depletion decreased to under 2 million km2 by the second week in November. This occurs as the polar vortex weakens and the hole fills in with ozone rich air from further north. However, this year a persistent pocket of air with more than 50% depletion continues to cover an area of 5-8 million km2, about half of the size of the present ozone hole. Ozone measurements made from balloons flown from the Antarctic continent during mid-November also confirm that the stratospheric ozone layer is only gradually recovering. Neumayer and Syowa stations on the edge of the continent are still well within the ozone hole as is the South Pole station with 50% depeletion. However, near normal ozone values, are currently being reported from some Antarctic stations, including Vernadsky and Marambio, and the South American stations of Ushuaia and Comodoro Rivadavia in Argentina.

4. Ozone hole characteristics: The area of the ozone hole has not decreased substantially in the past two weeks, having increased briefly then decreased again to about 12 million km2. This is almost 50% of the peak area of 25 million km2 in mid September. To remain so large this late in the year is most unusual, possibly exceeding all previous years. In previous 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 ozone data available from satellites and ground stations with the pre-ozone hole norms. The ozone mass deficit has decreased by 30% of its maximum value of 54 Mt from 20% two weeks ago. This contrasts with the ozone hole of 2000 which was the largest on record, but had completely disappeared by mid-November. With a vortex that is still strong, rather circular and remaining over the Antarctic continent, there is no sign that it will dissipate soon. The duration of the very low ozone values over Antarctica has a great influence on UV levels experienced in and near Antarctica. This is explained by increased UV intensity from the sun when it moves higher in the sky, as the Spring season progresses. UV is being continuously monitored in and near Antarctica by the NSF UV Monitoring Network.

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). UV data is provided by the U.S. National Science Foundation's UV Monitoring Network. 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 7/2001