Evidence for Arctic Ozone Depletion in Late February and early March 1994

Significant chemical ozone (O3 ) loss in the 1993-94 Arctic winter occurred mainly during an unusually late cold spell of approximately 10 days in late Feb/early Mar. Over the 30 d period studied (including the cold spell), observed vortex-averaged O3 at 465 K (approximately 40 hPa) decreased by approximately 10%. New three-dimensional, diabatic trajectory calculations show that this observed decrease represents only about half of the net chemical loss (approximately 20%) during the 30 day period. The resupply of lower stratospheric O3 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 O3 evolution during recent Arctic winters.