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/ozbull3.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 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 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.

3. The purpose of this bulletin is to continue to update the descriptions in the two previous WMO Ozone Bulletins, and to compare the current conditions with previous years. The low temperatures found over and near Antarctica during Winter activate chemical processes that in the presence of sunlight, result in rapid ozone depletion and result in the ozone hole. During August, much of Antarctica was still in darkness, limiting the area for rapid ozone loss. The sunlit area has increased significantly during August, and the low values characteristic of the ozone hole have emerged during early September. However, the rapid changes that are observed at a single location are not simply a result of chemical ozone loss occurring overhead. These localised changes also result from atmospheric circulation that continually moves air with differing ozone content from place to place. Therefore, it is expected that along with the steady march of lower and lower ozone within the polar vortex, localised increases will also be observed that reflect these atmospheric motions.

4. Preliminary ground-based measurements during the past two weeks from five Antarctic GAW stations reporting overhead ozone amounts all show substantial decreases when compared to the pre-ozone hole norms (WMO Scientific Assessment of Ozone Depletion: 1998). Dumont d'Urville, Marambio, Mirny, and Syowa observed 30% below norms, while King George Island and Vernadsky found 10%. Since 1 Sept. Dumont d'Urville, King George Island and Marambio have measurements that are 30% below norms while Mirny and Syowa have recorded very low values, 50% below the norms. The four GAW stations not on the Antarctic continent and reported in the last bulletin have seen a recovery in ozone to near normal values.

5. The latest TOMS satellite observations in the sunlit portion of Antarctica show an average decrease of about 35% below norms. A large crescent shaped area contains exceptionally low ozone for so early in the season and nearly circles the continent. Values 50% below norms constitute a substantial area within the crescent, consistent with the ground-based measurements reported from Mirny and Syowa. Although ozone decreases of this magnitude are common during each ozone hole season, it is remarkable to find these low values so early in Sept., perhaps one or two weeks earlier than in any previous year. This results in a larger than usual ozone hole for early Sept. Satellite ozone measurements averaged over the month of August show ozone was also exceptionally low outside the vortex region. Comparing latitude bands between the Antarctic vortex and latitude 50 S with all earlier satellite data, shows this years is the lowest on record for the month of August, 10% to 20% below the norms. Ozone further north is typical of recent years and near historical norms.

6. The extremely low temperatures that produce the polar stratospheric clouds that prime the atmosphere for ozone depletion continued throughout the period but with decreased frequency. As expected, temperatures are gradually warming at most levels and will continue to warm until the vortex dissipates in a few months and the ozone hole completely mixes into air from other latitudes.

7. The chemically primed vortex region has now begun the ozone loss process in earnest, and with an intensity exceeding all previous years. However, prevailing meteorological conditions in the stratosphere, particularly during the Austral Spring, strongly influence the overall extent of ozone loss and may substantially limit the total seasonal depletion.

END of WMO Antarctic Ozone Bulletin 3/2000