Evidence for Arctic ozone depletion in late February and early March 1994

Significant chemical ozone (O 3 ) loss in the 1993–94 Arctic winter occurred mainly during an unusually late cold spell of ∼10 days in late Feb/early Mar. Over the 30 d period studied (including the cold spell), observed vortex‐averaged O 3 at 465 K (∼40 hPa) decreased by ∼10%. New three‐dimensional, diabatic trajectory calculations show that this observed decrease represents only about half of the net chemical loss (∼20%) during the 30 day period. The resupply of lower stratospheric O 3 by transport in Feb 1994 was considerably greater than in 1993, when transport masked only about a quarter of the chemical loss in Feb/Mar. The net estimated chemical loss over 30 days in 1994 was comparable to that over the same 30 days in 1993, but mainly occurred at a faster rate during the brief cold spell. These results highlight the impact of Arctic interannual variability on the relative roles of chemistry and dynamics in O 3 evolution during recent Arctic winters.