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 web page for the Atmospheric Research and Environment Programme (AREP) at www.wmo.ch/web/arep/00/ozbull6.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. During the past two weeks the ozone hole has continued to decrease in area and is now about 30% of the record breaking size observed in early September. A slow decrease in size is normal after reaching a maximum usually during the month of September, but this year the decrease is rapid. When compared to other years, the ozone hole this year is the smallest of the past decade for the late October period. As the ozone hole rapidly dissipates through dilution with surrounding regions, the occurrence of very low ozone values and the resulting high UV Index over populated regions becomes less probable. Indeed, the low ozone and high UV Index values reported in this Bulletin two weeks ago for the southern tip of South America and the Falkland Islands have abated as the ozone hole weakened and moved over the South Atlantic Ocean.

3. Although not under the ozone hole during the past two weeks, the WMO Global Atmosphere Watch (GAW) stations at Ushuaia, San Julian and Comodoro Rivadavia, Argentina have reported average ozone values 10% to 15% below the 1964-76 pre-ozone hole norms, with lower ozone values during the first week. As the ozone hole moved eastward over the South Atlantic Ocean, ozone has recovered over South America and presently is near the early norms. A shift of the hole toward South America started in early October and resulted in the very low ozone values we reported for a few populated areas in mid October. Satellite images show that beginning 28 October, the ozone hole drifted off of the South Pole and now covers not more than 1/3 of the Antarctic continent. The somewhat elongated ozone hole now extends over a limited part of the South Atlantic Ocean where elevated UV Index levels have occurred intermittently.

4. Meteorological conditions in the lower stratosphere are known to strongly affect the intensity of the development of the ozone hole and the timing of its ultimate complete dissipation. This year is no exception, as the early and very strong development of the ozone hole was preceded by an unusually large and persistent area with the extremely low temperatures that initiate the ozone loss processes. The rapid decrease in size and the early dissipation of the exceptionally large area with more than 50% ozone depletion, may have resulted from mitigating meteorological conditions. In these Bulletins we have repeatedly pointed out the importance of temperature changes in the lower stratosphere, particularly for the Antarctic, where a measured cooling trend is evident since the early 1980s. Lower temperatures can extend or intensify the ozone loss period even as the chemicals that result in ozone destruction decrease. However, for this year, temperatures low enough to produce polar stratospheric clouds have currently all but completely disappeared, therefore a further decrease in the intensity of ozone loss within the ozone hole is expected in the coming weeks, as the dissipation of the ozone hole progresses.

5. Bulletins are based upon 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). The ERA-15 and daily T106 meteorological fields of ECMWF 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. If this bulletin is quoted, due credit should be given.

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 7/2000