On the response of a three-dimensional general circulation model to imposed changes in the ozone distribution

A series of idealized ozone perturbations has been studied with the French community general circulation model Arpege. The perturbations are uniform 50% and 75% reductions and an ozone hole type reduction concentrated in the lower part of the stratosphere and the upper part of the troposphere. We compare the radiative drive, the temperature response under the fixed dynamical heating approximation, and the full dynamical response. In all experiments the main effect of the dynamics is a weakening of the diabatic meridional circulation and an associated latitudinal smoothing of the temperature response. The weakening of the diabatic meridional circulation is in agreement with a reduction of the wave forcing, associated with an extended tongue of low refractive index close to the tropopause. While the fixed dynamical heating approximation in general represents the pattern of the temperature response well, the strength of the response is altered when allowing dynamical effects. In the lower stratosphere this adjustment is 25%-50% of the fixed dynamical heating response. The mean zonal wind is very stable to uniform reductions, but the strength of the winter stratospheric jet increases drastically in the hole type experiment. The ozone perturbations decrease the variability in the winter hemisphere, which in the control experiment and the uniform reduction experiments is of oscillatory nature with a timescale of 50 to 100 days.