Ozone and water vapour in the austral polar stratospheric vortex and sub-vortex,

In-situ measurements of ozone and water vapour, in the Antarctic lower stratosphere, were made as part of the APE-GAIA mission in September and October 1999. The measurements show a distinct difference above and be- low the 415 K isentrope. Above 415 K, the chemically per- turbed region of low ozone and water vapour is clearly evi- dent. Below 415 K, but still above the tropopause, no sharp meridional gradients in ozone and water vapour were ob- served. The observations are consistent with analyses of po- tential vorticity from the European Centre for Medium Range Weather Forecasting, which show smaller radial gradients at 380 K than at 450 K potential temperature. Ozone loss in the chemically perturbed region above 415 K averages 5 ppbv per day for mid-September to mid-October. Apparent ozone loss rates in the sub-vortex region are greater, at 7 ppbv per day. The data support, therefore, the existence of a sub- vortex region in which meridional transport is more efficient than in the vortex above. The low ozone mixing ratios in the sub-vortex region may be due to in-situ chemical destruction of ozone or transport of ozone-poor air out of the bottom of the vortex. The aircraft data we use cannot distinguish be- tween these two processes.