EVIDENCE OF SUBSTANTIAL OZONE DEPLETION IN WINTER 1995 96 OVER NORTHERN NORWAY/

In winter 1995/96, the stratospheric ozone layer over most of the Euro pean Arctic was exposed to extremely low temperatures and strong PSCs. At the same time, total ozone monitoring instruments at Tromso and An doya, Northern Norway, observed values up to 50% below the long-term a verage values of the Dobson instrument at Tromso. The deviation increa sed systematically with time of the year, reaching a maximum in early March. Measurements with the ozone DIAL system at the ALO-MAR facility at Andoya showed significant reduction Of ozone mixing ratios in the 430 to 580 K potential temperature region. A maximum reduction of almo st 50% occurred at about 500 K between early January and early March. Comparison with 3D model calculations revealed large reductions with r espect to passive tracer ozone profiles in the 400 tb 600. K region, r eaching a maximum of about 60% by the end of March at the 475 K level. The 3D chemical model showed ozone depletion in the same altitude reg ion as the measurements but seemed to underestimate the depletion syst ematically. The comparison also indicated ozone depletion of up to 30% in the 475 to 675 K region in extra-vortex air which remained close t o the vortex edge during a period in mid-March.