A smaller ozone hole for 2004
This year’s Antarctic ozone hole was smaller than those of recent years. According to a preliminary analysis of data from NASA’s Earth Probe satellite, the ozone hole reached a maximum area (on 21 September) of about 24 million square kilometres – similar in size to the North American continent.
The largest holes on record occurred in 2000 and 2003 and were about 30 million square kilometres in size. The growth of this year’s ozone hole was more gradual than in 2003 and resembled behaviour seen in the mid-1990s. Unlike the cold conditions of 2003, winter temperatures in the Antarctic stratosphere were near the long-term average. Polar Stratospheric Clouds (PSCs), which precondition the atmosphere and allow the ozone hole to form, were also less extensive than in 2003.
At Davis, the LIDAR detected the first substantial PSC layer of the season in early June, about four weeks later than for the previous year. Cloud sightings were also made by Davis and Mawson expeditioners around this time.
The first signs of ozone depletion over Antarctica began during late August. The lowest ozone values above Davis were reached during mid-September, when measurements by balloon-borne instruments showed a 40% reduction in total ozone compared with mean summer and autumn values.
Temperature disturbances in the upper stratosphere began to appear in early spring. This behaviour is an annual occurrence, although the disturbances were generally more pronounced than the long-term mean. As a result, PSCs quickly disappeared and the size of the ozone hole was in decline by the end of September.
Dr Andrew Klekociuk
Ice, Oceans, Atmosphere and Climate Program,
Australian Antarctic Division