World Meteorological Organization

1. The Secretariat of the World Meteorological Organization (WMO) distributes Bulletins providing information on the state of the ozone layer above the Antarctic during the period August-December each year. Bulletins are distributed via the WMO-Global Telecommunication System (GTS) and are also available on the internet through the WMO web page for the Atmospheric Research and Environment Programme (AREP) at www.wmo.ch/web/arep/00/ozbull2.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. 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, 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 Bay), Uruguay (King George Isl.), and USA (South Pole). Satellite ozone data are also used and provided by NASA - Total Ozone Mapping Spectrophotometer (TOMS) and by the 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 size 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.

1. The purpose of this bulletin is to update the description found in WMO Ozone Bulletin #1/2000 of the early conditions over Antarctica that were based upon data prior to 11 August 2000, and to compare these current conditions with previous years. As discussed in the last bulletin, low temperatures activate chemical processes that in the presence of sunlight, result in the rapid ozone depletion that annually produces the "ozone hole". During August, much of Antarctica is still in darkness, limiting the area possible for ozone measurements by those ground-based and satellite instruments that require sunlight. However, with the increased sunlit area since the last bulletin, more ozone data have become available around the perimeter of the continent. During the last two week period, near real-time ground-based data have been sent directly to WMO, which, along with analysis of daily satellite images and of meteorological parameters, describe the evolving conditions affecting ozone loss over Antarctica. To better understand these evolving conditions, a historical perspective is added by comparing current conditions with those of previous years. Averaged ground-based data from 1964-76 (WMO Scientific Assessment of Ozone Depletion: 1998) are used to infer changes in current ozone amounts from pre-ozone hole conditions, and data from more recent years are also compared.
2. Preliminary ground-based measurements during August 16-22 from the four Antarctic GAW stations reporting overhead ozone amounts all show substantial decreases when compared to the pre-ozone hole period (1964-76), with Dumont d'Urville 20% below, Mirny 35% below, and both Syowa and Vernadsky reporting 25% below. Both Syowa and Vernadsky have ozone records extending back more than 25 years that indicate the Syowa weekly average is the second lowest on record while for Vernadsky this year is the lowest. There are presently four GAW stations not on the Antarctic continent but poleward of 45 S latitude that are also reporting preliminary data during this season. Of these, Comodoro Rividavia (46 S) and San Julian (49 S) are 15% below their 1964-76 norms, Kerguelen Island (49 S) is 5% above its norm, while Ushuaia (55 S) has recorded 20% below, the lowest in its 6 year record of measurements.
3. The latest satellite observations in the sunlit portion of the Antarctica perimeter, show an average decrease of about 30% in the total amount of ozone overhead when compared to the 1964-76 norms. This is double the 15% reported two weeks ago and unusual for this early period. The low temperatures that prime the atmosphere for ozone depletion continued throughout the period, and temperatures at and below -93 C can be found at 20 km altitude each day during the period. Temperatures low enough for PSC formation continued to cover more than 60% of the vortex area. The lowest temperatures for the season have apparently been reached, and gradual warming is now expected. This will result in a corresponding decrease in PSC formation.
4. The vortex region remains chemically primed for the expected ozone loss that is already well underway. The amount and extent of loss has appeared earlier than in previous years. The sunlit region surrounding Antarctica continues to have considerably less ozone than normal, and has been demonstrated with both ground-based and satellite measurements. However, prevailing meteorological conditions in the stratosphere, particularly during the Austral Spring, strongly influence the extent and intensity of ozone loss and may substantially reduce the total seasonal depletion.

END of WMO Antarctic Ozone Bulletin 2/2000