WMO Antarctic Ozone Bulletin #2/2001 Issued on 7 September 2001

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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: Minimum temperatures measured in the lower stratospheric remain low over Antarctica, but are about 3-4 C warmer than during the same period last year. The area with temperatures low enough to form polar stratospheric clouds (PSCs) remain virtually identical to early September last year, at 20-25 million square kilometres (million km2), about 2/3 the size of the polar vortex. The PSCs activate chemical processes, that in the presence of sunlight, result in rapid ozone depletion. During August, much of Antarctica remains in total darkness, limiting the area for rapid ozone loss. By early September, the sunlit area has increased, and the ozone hole is now clearly evident. Also during this period, the temperatures are increasing from their very low wintertime levels, and it is expected that the area with PSCs will continue to decrease.

3. Observed ozone changes: Two measurement programmes provide ozone data over Antarctica, both independently recording the ozone changes that occur each year. One is the WMO Global Atmosphere Watch network of ground based stations, and the other source of data is provided by instruments on satellites. Near real-time ground-based data are sent directly to WMO, and nearly global coverage of daily satellite measurements provide complimentary views of the rapidly changing conditions that are currently underway. Averaged ground-based measurements from 1964-76 are used to infer changes in current ozone amounts from pre-ozone-hole conditions. Ground-based measurements averaged during the first week in September were well below these pre-ozone-hole norms at Dumont d'Urville (20%), Mirny (25%), Rothera Island (20%), and Syowa (35%). The Argentine city of Ushuaia at the southern tip of South America also recorded low values, about 10% below the norms, while Comodoro Rivadavia was near normal. Satellite measurements also shows that present values range from 20% to 40% below norms.

4. Ozone hole characteristic: By early September, ozone loss is sufficient to identify the area with ozone values characteristic of the ozone hole. Last year, the size of the ozone hole was reported as the largest on record, at about 28 million km2 during the second week of September. This year the area reached about 24 million km2 on 4 September and appears to be increasing at nearly the same rate as last year. The shape of the early September ozone hole is more circular than last year, indicating a more stable vortex this year. A measure of the amount of ozone loss can be expressed in millions of tons (MT) of ozone and estimated from the daily ozone data available. This "ozone mass deficit" is calculated within the area more than 10% below pre-ozone-hole norms and provides a means of measuring the progress of the depletion and for comparing ozone holes from different years. Last years ozone hole reached its maximum of 57 MT by the second week in September, a value higher than all previous years. This year the ozone mass deficit has reached 53 MT during the first week of September, and judging from past years, it can be expected to continue to increase until at least mid-September.

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 2/2001

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