Past and future conditions for polar stratospheric cloud formation simulated by the Canadian Middle Atmosphere Model P. Hitchcock, T. G. Shepherd, and C. McLandress Department of Physics, University of Toronto, Toronto, ON, Canada
Abstract. We analyze here the polar stratospheric temperatures in an ensemble of three
150-year integrations of the Canadian Middle Atmosphere Model (CMAM), an
interactive chemistry-climate model which simulates ozone depletion and
recovery, as well as climate change. A key motivation is to understand possible
mechanisms for the observed trend in the extent of conditions favourable for
polar stratospheric cloud (PSC) formation in the Arctic winter lower
We find that in the Antarctic winter lower stratosphere, the low temperature
extremes required for PSC formation increase in the model as ozone is depleted,
but remain steady through the twenty-first century as the warming from ozone
recovery roughly balances the cooling from climate change. Thus, ozone depletion
itself plays a major role in the Antarctic trends in low temperature extremes.
The model trend in low temperature extremes in the Arctic through the latter
half of the twentieth century is weaker and less statistically robust than the
observed trend. It is not projected to continue into the future. Ozone depletion
in the Arctic is weaker in the CMAM than in observations, which may account for
the weak past trend in low temperature extremes. In the future, radiative
cooling in the Arctic winter due to climate change is more than compensated by
an increase in dynamically driven downwelling over the pole.
Citation: Hitchcock, P., Shepherd, T. G., and McLandress, C.: Past and future conditions for polar stratospheric cloud formation simulated by the Canadian Middle Atmosphere Model, Atmos. Chem. Phys., 9, 483-495, doi:10.5194/acp-9-483-2009, 2009.