LOCALIZED RAPID OZONE LOSS IN THE NORTHERN WINTER STRATOSPHERE - AN ANALYSIS OF UARS OBSERVATIONS

Observations of low-ozone air pockets forming during northern winter i n the middle stratosphere outside the polar vortex provide an opportun ity to test models of the photochemistry of ozone at several altitudes , as the trajectories of the associated air parcels are well defined b y Lagrangian transport codes over the periods of interest, and vertica l profiles of key species, including ozone, are available from instrum ents aboard the Upper Atmosphere Research Satellite (UARS). We find th at a Lagrangian photochemical model, where the chemistry within an iso lated parcel of air is simulated as it travels along a specified traje ctory, does reproduce the observed formation of low-ozone pockets in t he 6-10 mbar altitude range within the measurement uncertainties but o verestimates the ozone loss rate at higher altitudes. The rapid ozone loss localized in these pockets is due to the isolation of air at high latitudes (and high solar zenith angles). Thus the low ozone levels a re due to a decrease in the odd oxygen production rate and not to an i ncrease in the loss rate by reaction with halogen species, as in the ' 'classical'' ozone hole.