A technique for estimating polar ozone loss: Results for the northern 1991/92 winter using EASOE data

In this paper we describe a technique for estimating chemical ozone loss in the Arctic vortex. Observed ozone and temperature profiles are combined wi th the model potential vorticity field to produce time series of vortex ave raged ozone mixing ratios on chosen isentropic surfaces. Model-derived radi ative heating rates and observed vertical gradients of ozone are then used to estimate the change in ozone that would occur due to diabatic descent. D iscrepancies with the observed ozone are interpreted as being of chemical o rigin, assuming that there is negligible horizontal transport or mixing of air into the vortex. The technique is illustrated using ozone sonde measure ments collected during the 1991/92 European Arctic Stratospheric Ozone Expe riment (EASOE), meteorological analyses from the European Centre for Medium -range Weather Forecasts (ECMWF) and radiative heating rates extracted from the Global Atmospheric Modelling Programme (UGAMP) 3D General Circulation Model. Our results show that there was photochemical ozone destruction insi de the Arctic vortex in early 1992 with a loss between 475 K and 550 K (aro und 20 km) of 0.32 +/- 0.15 ppmv in the first 20 days of January, equivalen t to a rate of 0.51 +/- 0.24%/day (at the 95% confidence level).