The effect of stratospheric ozone depletion on the phase of the Antarctic Oscillation

The effect of stratospheric ozone loss on Southern Hemispheric extratropica l circulation is explored using an atmosphere-only model. The main troposph eric response is a sudden shift in the leading mode of month-to-month varia bility, the Antarctic Oscillation, during November and December towards its high phase. Therefore, this change consists of a shift in atmospheric mass from high-latitudes poleward of 60 degreesS to a midlatitude band centred on 45 degreesS. This response provides a plausible explanation for the incr ease in westerly circulation at 60 degreesS observed since the early 1980's . There is also a strong response in January-March but this may be unrealis tic as the observed lower stratospheric temperature changes are poorly simu lated in that season.