Evidence of the mid-latitude impact of Antarctic ozone depletion

Abstract

THE 1987 Antarctic Airborne Ozone Expedition established that the springtime depletion of Antarctic ozone^1,2 is due to photochemical destruction³ following a preconditioning phase involving heterogeneous reactions on polar stratospheric clouds⁴. Ozone destruction is concentrated in the cold Antarctic stratospheric vortex of winter and early spring, where these clouds occur. Nevertheless, ozone data reveal a secular decline into mid-latitudes^5,6. Modelling studies^6,7 suggest a 'dilution effect' whereby ozone-poor air is transported into mid-latitudes when the vortex breaks up in late spring (the 'final warming'). The extent to which the effect penetrates into middle latitudes is clouded by statistical uncertainty in trend analyses and by the difficulty of separating photochemical and dynamical effects on seasonal timescales. Here we analyse record low ozone values found over Australia and New Zealand during December 1987⁵ following the record low Antarctic values of October 1987⁵. In fact, there was a sudden decline of ozone amounts in mid-month; this rules out photochemical effects as a cause and allows us to investigate the underlying processes on a 'case study' basis. Using data from ozonesondes, radiosondes, the Nimbus-7 total ozone mapping spectrometer (TOMS), and meteorological analyses from the National Meteorological Center (Washington), we argue that these low values resulted from transport of ozone-poor air from higher latitudes. It therefore seems that the chemical destruction of ozone over Antarctica in early spring is having an impact on lower latitudes.