Dependence of model‐simulated response to ozone depletion on stratospheric polar vortex climatology. Issue 12 (28th June 2017) - Lin, Pu
Abstract: We contrast the responses to ozone depletion in two climate models: Community Atmospheric Model version 3 (CAM3) and Geophysical Fuild Dynamics Laboratory (GFDL) AM3. Although both models are forced with identical ozone concentration changes, the stratospheric cooling simulated in CAM3 is 30% stronger than in AM3 in annual mean, and twice as strong in December. We find that this difference originates from the dynamical response to ozone depletion, and its strength can be linked to the timing of the climatological springtime polar vortex breakdown. This mechanism is further supported by a variant of the AM3 simulation in which the southern stratospheric zonal wind climatology is nudged to be CAM3‐like. Given that the delayed breakdown of the southern polar vortex is a common bias among many climate models, previous model‐based assessments of the forced responses to ozone depletion may have been somewhat overestimated. Key Points: Models forced with identical ozone depletion can yield different lower stratospheric cooling The difference is due to a dynamical feedback dependent on the polar vortex climatology Biases in the polar vortex climatology may lead to incorrect response to ozone depletion