MLS observations of Arctic ozone loss in 1996–97

The Microwave Limb Sounder (MLS) observed ozone (O 3 ) loss in the Arctic vortex beginning in January 1997 at 585 K (∼25 hPa) and in February 1997 at 465 K (∼50 hPa). Minimum vortex‐averaged O 3 mixing ratios observed in 1997 were higher than those in 1996, which were the lowest ever recorded by MLS. The vertical extent of O 3 loss and maximum local O 3 decreases were larger, but the decrease filled the vortex less completely, in 1997 than in 1996. Unusually low high‐latitude column O 3 above 100 hPa in April 1997 resulted mainly from dynamical effects of the unusually persistent lower stratospheric vortex and winter‐like temperature patterns. Column O 3 above 100 hPa averaged in comparable regions of the vortex showed a stronger decreasing trend in 1996–97 than in 1995–96, consistent with the larger vertical extent and maximum local values of lower stratospheric O 3 loss. Chemical O 3 loss resulted in an ∼10% observed decrease in column O 3 between late January and early April 1997.