Low ozone concentrations over Macquarie Island during 1997 Part I: trajectory analysis

Ozone concentrations have been decreasing globally for the last 20 years in part due to increasing chlorine concentrations in the stratosphere (WMO 1999). The most dramatic example of these reductions has been identified in the high latitude southern hemisphere, where ozone levels are nearly entirely depleted in the lower stratosphere during September and October each year. This phenomenon, which is commonly referred to as the Antarctic ozone hole, has become a regular feature of the springtime high southern latitudes. While the severity of the Antarctic ozone hole has remained nearly constant during the last decade, significant year to year variability has been observed (WMO 1999). The amount of total ozone over a particular location has natural variations due to both chemical and dynamical processes. In the southern hemisphere, the maximum observed total column ozone occurs during the spring between 45°S and 60°S. This is primarily due to the large-scale transport of ozone rich air from the tropical stratosphere to the southern middle latitudes. This region of higher ozone air in the middle latitudes normally surrounds relatively lower ozone air present in the polar region. Thus there are large meridional gradients in ozone concentrations between the polar and middle latitudes. Indeed, these meridional ozone gradients have recently increased due to anthropogenic ozone loss occurring over Antarctica in spring. In winter, the strong winds of the polar vortex largely inhibit meridional exchange between the middle and high latitudes, and thus prevent the large-scale transport of middle latitude ozone rich air into the high latitudes. During spring, the normally circumAust. Met. Mag. 51 (2002) 85-94