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. A decrease in total column ozone (the amount of ozone overhead) can result in an increase of UV-B radiation striking the earth's surface below. In cloudless conditions, the higher the sun is in the sky, the greater are the UV-B levels that impact the biosphere. To help the general public evaluate possible exposure to damaging UV radiation where they live, scientists have defined a parameter called the UV Index that is related to the well known erythemal effects of solar UV on human skin. An international standard UV Index has been established through a joint recommendation from WMO, WHO, UNEP and INCIRP and is used throughout the world in operational weather reports and forecasts to inform the public about their local UV levels. UV Index values of 1-3 are considered to represent low exposure, 4-6 medium, 7-9 high, and 10 and above to be extreme.

3. During the past two weeks the ozone hole has continued to decrease in extent (area) and is now about 2/3 the maximum observed in early September. When compared to the past decade it is now about average. Although smaller, the hole has shifted toward South America, with very low ozone values stretching from the South Pole to the tip of the Antarctic Palmer Peninsula, and near normal (pre-ozone hole) values common on the Australian side of the Antarctic continent. Measurements at the WMO GAW station near the city of Ushuaia, Argentina, have shown the ozone hole has been overhead during 9 of the past 14 days. Measurements also show that the town of San Julian, Argentina, (49 S) 500 km to the north, was also within the hole on 12 and 18 Oct. Satellite measurements show the hole over the Falkland Is., Punta Arenas, Chile, and the Argentine cities of Rio Grande and Rio Gallegos on 12 October. NILU has calculated the UV Index (assuming mid-day sun and clear sky) for this region indicating that except for 15 Oct., the index was over 7 on the days of 11-18 Oct. In fact, on 12 Oct., the UV Index was more than 11 for Rio Grande, Ushuaia, and Punta Arenas, and for the Falkland Is. it was more than 11 on 13 October. The Index was over 9.75 for those locations also on 18 Oct. The extreme values above 11 are typical of the tropics, and values over 7 are considered to be a high exposure. Therefore, during this one week period, people in the southern tip of South America and the Falkland Is. would have been at a higher than normal risk for sunburn wherever there were clear sky conditions at mid-day.

4. The record depth (average deviation from pre-ozone hole norms) reported in Bulletin #5 for the last 10 days of Sept. continued, with the average of the first 10 days of Oct. revealing more than 60% depletion in some areas. However, since that time the depth of the hole has decreased markedly, particularly during the past two days. Using previous years as a guide, the decrease in the intensity of this years ozone hole can be expected to continue in the coming weeks.

5. Variations in the meteorological conditions in the stratosphere affect the extent of the ozone hole, its depth, and its persistence. Temperatures low enough to produce polar stratospheric clouds have abated significantly, and presently cover less area than in the past few years for the same period. This may partially explain the apparent rapid recovery during the past week from the record breaking values reported earlier.

6. 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 6/2000