The atmospheric circulation response to climate change-like thermal forcings in a simple model

The expected global temperature changes due to increased greenhouse gases, as well as observed stratospheric polar cooling due to ozone depletion, will likely drive changes in the atmospheric circulation. Observations, as well as climate change simulations from the Intergovernmental Panel on Climate Change 4th Assessment Report (IPCC AR4), indicate that these changes may include a poleward shift of the storm tracks and a widening of the Hadley cell. We use a simple dry dynamical model and impose idealized thermal forcings at the surface, the tropical troposphere, and the polar stratosphere in order to understand how these temperature changes and corresponding changes in the meridional temperature gradient affect the atmospheric circulation. We find that enhanced warming in the tropical troposphere drives a poleward shift of the storm tracks in both hemispheres as well as an expanded Hadley circulation. Polar stratospheric cooling enhances the poleward shift of the jets, although the tropospheric response is sensitive to the location of the forcing in the stratosphere. Warming at the polar surface, on the other hand, causes an equatorward retreat of the storm track. Transient simulations are used to interpret the mechanisms behind these changes.