No abstract

A stratospheric-chemistry model coupled to a general-circulation model is used to investigate chemistryclimate coupling processes and their influence on ozone. Simulations commence on 1 March in each of the years 2014, 2024, 2034, 2044 and 2054, and consist of a 4-month spin-up period, followed by a I-year integration.Projected values of halogen amounts and greenhouse gases are imposed on the model. During the period 2 0 1 4 54, ozone generally increases but by 2054 has still not returned to 1980 conditions. In Antarctica, spring ozone recovers temporarily in the 2024 integration but the ozone hole deepens significantly again in the 2034 and 2044 integrations before finally disappearing in the 2054 integration. The results suggest that the deepening of the Antarctic ozone hole in the model in 2034 and 2044, despite a reduction in halogen loading, is due to enhanced cooling due to increased greenhouse gases. Model-predicted temperature and ultraviolet (UV) changes are also investigated. It is found that recovery of ozone during the period of the simulations gives rise to reduced stratospheric temperature decreases and UV levels are still slightly higher in general than in previous calculations for 1980.

One-year simulations of stratospheric chemistry are performed in a general-circulation model (GCM). A fairly comprehensive description of stratospheric chemistry is included in a state-of-the-art GCM which has been extended to the middle mesosphere. The predicted ozone concentration is used in the model radiation scheme, thereby coupling the dynamical and chemical processes. consist of a 4 month spin-up period, followed by a 1-year integration. Past and projected values of halogen amounts and greenhouse gases (GHGs) are imposed on the model. The results for 1979-80 and 1994-95 are generally in good agreement with observations, indicating in the latter case a deep Antarctic ozone hole and some Arctic ozone loss. For the 1979 simulation only a very shallow ozone hole was simulated, in agreement with observations. In about the year 2005, the Antarctic ozone hole reaches its maximum size and globally averaged ozone reaches its minimum, depending on the month. Tropical ozone continues to decrease until about 2010. Results in the Arctic are dominated by interannual variability, but minimum ozone may not be attained until the year 2010. The results suggest that the increase in GHGs is delaying the onset of ozone recovery. Relative to 1980 conditions, the model changes in ozone result in small predicted increases in surface ultraviolet radiation in the Arctic and mid-latitude summer but large increases in the tropics and in the Antarctic summer.