THE INFLUENCE OF CLIMATE-CHANGE AND THE TIMING OF STRATOSPHERIC WARMINGS ON ARCTIC OZONE DEPLETION

Satellite data are presented showing the timing of sudden warmings in the lower stratosphere during the winters 1979-1992. A three-dimension al dynamical-radiative-photochemical model is used to establish how Ar ctic ozone depletion will respond to a doubling of CO2 according to th e timing of the warmings. In a series of idealized experiments the tim ing of the warmings is varied by specifying different geopotential wav e amplitudes at the 316-mbar model lower boundary. Results from a ''tr ansient climate change experiment'' show that the chosen wave amplitud es are appropriate for both the current and the doubled CO2 atmosphere . For doubled CO2 the experiments show that any significant risk of an Arctic ozone hole will be confined to those years with only a late st ratospheric warming. In all other years the results suggest that sprin gtime total ozone over the Acetic is more likely to increase by a smal l amount due to a combination of slower homogeneous chemistry and chan ges in transport. The predictions obtained from the idealized studies are then tested by prescribing at the model lower boundary the observe d geopotential wave amplitudes from two specific years with late winte r warmings. Doubling CO2 amounts produced no significant increase in o zone depletion with the 1989 wave amplitudes, but with 1990 wave ampli tudes, an Arctic ozone hole occurred with minimum column of 187 Dobson Units. This contrasting response is attributed to the large midwinter pulse in the 1989 wave amplitudes compared to the less dramatic and s horter timescale fluctuations in the 1990 wave amplitudes. It is concl uded that under doubled CO2 conditions an Arctic ozone hole is likely to occur in years with late stratospheric warmings following winters i n which there were no significant pulses in the upper tropospheric pla netary wave amplitudes.