Robustness of the Simulated Tropospheric Response to Ozone Depletion

Abstract

AbstractRecent studies have shown large intermodel differences in the magnitude of the simulated response of the Southern Hemisphere tropospheric circulation to ozone depletion. This inconsistency may be a result of different model dynamics, different ozone forcing, or statistical uncertainty. Here the summertime tropospheric response to ozone depletion is analyzed in an array of climate model simulations with incrementally increasing complexity. This allows the sensitivity of the response to a range of factors to be carefully tested, including the choice of model, the prescribed sea surface temperatures and greenhouse gas concentrations, the inclusion of a coupled ocean, the temporal resolution of the prescribed ozone concentrations, and the inclusion of interactive chemistry. A consistent poleward shift of the extratropical jet is found in all simulations. All simulations also show a strengthening of the extratropical jet and a widening of the southern edge of the Hadley cell, but the magnitude of these responses is much less consistent. However, in all simulations statistical uncertainty due to interannual variability is found to be large relative to the size of the response, despite considering long (100 yr) annually repeating simulations. It is therefore proposed that interannual variability is a dominant cause of intermodel differences in past studies, which have generally analyzed shorter, transient simulations.