Seasonality of polar surface warming amplification in climate simulations

The IPCC AR4 global warming climate simulations reveal a pronounced seasonality of polar warming amplification with maximum warming amplification in winter and minimum in summer. In this paper, we study the relative importance of surface albedo feedback (SAF), changes in cloud radiative forcing (CRF), changes in surface sensible and latent heat fluxes, changes in heat storage, and changes in the clear-sky downward infrared radiation in causing the strong seasonality of polar warming amplification by calculating partial temperature changes due to each of these processes using the surface energy budget equation. The main thermodynamic factor for a small polar warming amplification in summer is that the positive SAF is largely cancelled out by the negative surface CRF feedback in summer. The positive SAF is relatively much weaker in winter compared to its amplitude in summer, therefore does not contribute to the pronounced polar warming amplification in winter. The seasonal cycle of polar surface warming amplification, in terms of both spatial patterns and temporal amplitude, closely follows the seasonal cycle of the warming due to changes in clear-sky downward longwave radiation alone, indicating the importance of the atmospheric processes, such as water vapor feedback and dynamical feedbacks associated with the enhancement of poleward moist static energy transport, in causing the pronounced seasonality of polar warming amplification. Citation: Lu, J., and M. Cai (2009), Seasonality of polar surface warming amplification in climate simulations, Geophys. Res. Lett., 36, L16704, doi:10.1029/2009GL040133.