Is the polar amplification of surface air temperature driven by tropical forcing?

We examine whether changes in tropical convection can trigger the polar amplification of surface air temperature in the Northern Hemisphere winter between the periods of 1958-1977 (P1) and 1982-2001 (P2). This question was tested with an idealized general circulation model by perturbing the P1 climatological state with the P2-P1 tropical convective heating, estimated from ERA-40 precipitation data. It is shown that the circulation response closely resembles the observed P2-P1 pattern. Moreover, the adiabatic warming and horizontal temperature advection associated with this circulation response compares well with the observations. In analogy to water vapor transport, we also examined the passive tracer transport associated with this circulation. The tracer evolution shows reasonably good agreement with the observed trend in downward infrared-radiation (IR) in the Western Hemisphere. An ensemble of 50 model runs with their initial field randomly taken from the ERA-40 daily data exhibits essentially the identical circulation response and the dynamical warming, suggesting that this mechanism is insensitive to initial background flow.