Three-dimensional chemical model simulations of the ozone layer: 1979-2015

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. Simulations commence on 1 March in each of the years 1979, 1994, 1999, 2004, 2009 and 2014, and 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.