WMO Antarctic Ozone Bulletin #8/2000 Issued on 23 November 2000

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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 web page for the Atmospheric Research and Environment Programme (AREP) at www.wmo.ch/web/arep/00/ozbull8.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. Although it was the largest and the deepest ozone hole on record in September, during the past three weeks this year's ozone hole continued the rapid dissipation reported in Bulletin #7. Beginning in late October, it was the smallest of the past decade, and during the past week it has completely dissipated, the earliest since 1991. In contrast, the 1999 ozone hole was very persistent, retaining more than half of its maximum mid-September area into mid-November. This year, on 18 November, satellite data show that what remained of the ozone hole split into two small and roughly equal parts, one that remains over and near the Antarctic continent while the other has drifted northward, touching the southern tip of Africa. Since the split, the air with ozone values characteristic of an ozone hole has diluted with surrounding regions, leaving the two areas with ozone values that are about 20-30% lower than historical norms. These low overhead ozone amounts allow for significantly increased UV at the ground, although they are too high to qualify as an ozone hole. Measurements made at the WMO GAW stations and by satellites indicate that ozone is within about 10% of the pre ozone hole norms over much of Antarctica and most of the Southern Hemisphere.

3. It was reported in Bulletin #5 that when meteorological data are averaged over the years 1995-99, the area with temperatures low enough for polar stratospheric cloud (PSC) formation during October was double that found during any earlier 5 year period (since 1980). It was suggested that this apparent change in meteorological conditions over Antarctica may be responsible for the notable persistence of the ozone hole into November in recent years. Consistent with the rapid dissipation of the ozone hole this year, the area with these low PSC temperatures was somewhat diminished during October, particularly during the latter half. For the first time since 1992, PSC activity this year ceased by November 1. Such 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 was 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 PSC temperatures that initiated the ozone loss processes and its early demise was announced by an early warming.

4. This is the last WMO Antarctic Ozone Bulletin to be issued this year, although a complete summary of the WMO year 2000 Bulletins will be become available during December 2000. Suggestions concerning improving the Bulletins in the future as well as comments on this years Bulletins can be sent to the email address given below.

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 8/2000

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