Recovery of stratospheric ozone in calculations by the Center for Climate System Research/National Institute for Environmental Studies chemistry-climate model under the CCMVal-REF2 scenario and a no-climate-change run

Return times to 1980 values of ozone and the halogen concentrations in the future atmosphere were examined using the outputs of the Center for Climate System Research/National Institute for Environmental Studies chemistry-climate model (CCM). The CCM calculation for the future atmosphere was performed for the period of 1975-2100 under a future scenario of time-varying halogens, greenhouse gases, and sea surface temperatures for chemistry-climate model validation (CCMVal-REF2 scenario). A sensitivity test of a no-climate-change run for the future atmosphere was also performed, in which the concentrations of CO2, CH4, and N2O were fixed at those for 1975, and the sea surface temperature was fixed at that for the 1970-1979 mean, while the halogen concentrations were changed following the REF2 scenario. A comparison of the return time to 1980 values in these two runs was made. The return times of the halogen concentrations and column ozone in the extratropics for the REF2 run are earlier than those for the no-climate-change run, influenced by an enhancement of the meridional circulation and stratospheric cooling in the atmosphere. In the tropics, the column ozone of the REF2 run shows a second decrease after 2050, influenced by a stronger upward motion in the future atmosphere than in the present atmosphere. Trends in the zonal mean ozone concentration, zonal mean temperature, zonal mean zonal wind, Eliassen-Palm (EP) flux, EP flux divergence, vertical component of the residual mean meridional circulation, and chemical forcing to the ozone concentration are examined in the periods of 2000-2050 and 2051-2100. These trends in the dynamical and chemical factors explain the earlier return times of halogens and ozone in the extratropics of the REF2 run than in the no-climate-change run. In the no-climate-change run, a better correlation between the return time of column ozone to the 1980 level and that of the lower stratospheric halogen concentration is calculated for the Southern Hemisphere corresponding to the facts that the ozone concentrations in the Southern Hemisphere lower stratosphere are more controlled by chlorine and bromine chemistries than those in the Northern Hemisphere.