Towards understanding the extratropical atmospheric circulation response to anthropogenic forcing

Climate change experiments run on IPCC-class numerical models consistently suggest that increasing concentrations of greenhouse gases will lead to a poleward shift of the mid-latitude jets and their associated eddy fluxes of heat and potential vorticity. Experiments run on idealized models suggest that the poleward contraction of the jets can be traced to the effects of increased latent heating and thus locally enhanced warming in the tropical troposphere. In this work we provide new insights into the dynamics of the circulation response to tropical tropospheric heating using transient experiments in an idealized general circulation model. It is argued that the response of the mid-latitude jets to anthropogenic forcing can be interpreted in the context of: 1) the effect of tropical heating on the meridional slope of lower tropospheric isentropic surfaces; 2) a diffusive eddy response to the resulting changes in the isentropic slope; and 3) barotropic changes in the flow that are driven by the meridional shift in lower tropospheric wave generation.