WMO Antarctic Ozone Bulletin #1/2001 Issued on 23 August 2001

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2. The purpose of this first Antarctic bulletin for the year 2001 is to describe the early meteorological conditions found this year near and over Antarctica, that set the stage for the annual development of the ozone hole. It is low temperatures that activate chemical processes which in the presence of sunlight, result in the rapid ozone depletion that annually produces the "ozone hole". Temperatures must be sufficiently low to form polar stratospheric clouds (PSCs) to initiate these chemical conditions. Threshold temperatures of -78 C can produce PSCs, while lower temperatures (below -85 C) can further accelerate the chemical processing. The Antarctic polar vortex (the polar night jet) is a region with high velocity winds in the stratosphere that generally circle the Antarctic continent. This vortex region (the vortex and the area poleward) includes the lowest temperatures and the largest ozone losses that occur anywhere in the world. During August, satellite measurements of ozone distributions near Antarctica also provide some insights into the development of ozone loss, but only in the sunlit regions where the losses occur.

3. The processes that prime the atmosphere for ozone depletion are well underway. Meteorological data show that minimum temperatures this winter have not been as low as the year 2000, although the area with temperatures low enough to form PSCs has been about 25 million square kilometres since mid July, much like last year. This represents about 75 % of the total area presently within the vortex. As expected, the lowest temperatures for the season have been reached, and a gradual warming is occurring as the sun rises over Antarctica. It appears that the conditions necessary for ozone depletion over Antarctica are now in place, with temperatures sufficiently low to have chemically primed the vortex regions for ozone loss.

4. Preliminary ground-based measurements during the last two weeks from the four Antarctic WMO/GAW stations reporting overhead ozone amounts all show substantial decreases when compared to the pre-ozone hole period (1964-76). Dumont d'Urville has measured values 10% below, Mirny and Syowa both reported 20% below, and Vernadsky 15% below. The stations Mirny, Syowa, and Vernadsky have reported a few days 30% below norms, values usually considered within the ozone hole. The city of Ushuaia, Argentina, on the southern tip of South America has measured values averaging 15% below norms for the past two weeks, while Comodoro Rivadavia, a mid-latitude Argentine city has reported values 5-10% below pre-ozone hole norms. On the opposite side of the pole, the Australian mid-latitude station at Macquarie Island reports near normal values.

5. Much of the perimeter of the Antarctic continent is now sunlit during part of the day. The latest observations from this sunlit ring, shows an average decrease of about 25% in the total amount of ozone overhead, when compared to the pre-ozone hole period of 1964-76. In the coming weeks, chemical ozone loss is expected to continue, comparable to that of previous years. Prevailing meteorological conditions in the stratosphere will strongly influence the geographic extent and the duration of the period of intense ozone loss.


Questions regarding the scientific content of this bulletin should be addressed to


END of WMO Antarctic Ozone Bulletin 1/2001


