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Climate Dynamics

, Volume 29, Issue 2–3, pp 305–317 | Cite as

Polar amplification as a preferred response in an idealized aquaplanet GCM

  • Peter L. LangenEmail author
  • Vladimir A. Alexeev
Article

Abstract

An aquaplanet atmospheric general circulation model (GCM) coupled to a mixed layer ocean is analyzed in terms of its polar amplified surface temperature response to a 2×CO2-like steady forcing and in terms of the phase space trajectory of the relaxation of a free perturbation to equilibrium. In earlier studies concerned with linear stability analysis of the same system we have shown that the least stable mode of the linearized surface budget operator has a polar amplified shape. We demonstrate that this shape of the least stable mode is responsible for the polar amplified shape of the response to a uniform forcing and for the manner in which the system relaxes back to equilibrium. Based on GCM and simple energy balance model results it is argued that the decay time-scale of this mode is determined by the sensitivity of the net top-of-atmosphere radiation to surface temperature while its shape (and thus the degree of polar amplification in a climate change experiment) is determined by the sensitivity of poleward heat transports to low- and high-latitude temperatures by the faster time-scale atmospheric dynamics. This implies that the underlying mechanisms for the polar amplification may be obscured when studying feedbacks during the slow evolution of climate change or considering only the new equilibrium state after introduction of a steady forcing.

Keywords

General Circulation Model Heat Transport Outgoing Longwave Radiation Stable Mode Energy Balance Model 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

This research is supported by the Carlsberg Foundation and National Science Foundation Agreement No. ARC-0327664. This work was supported in part by a grant of HPC resources from the Arctic Region Supercomputing Center at the University of Alaska Fairbanks as part of the Department of Defense High Performance Computing Modernization Program. The suggestions by two anonymous reviewers substantially improved both the content and the clarity of the manuscript.

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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Ice and Climate Research, Niels Bohr InstituteUniversity of CopenhagenCopenhagen ODenmark
  2. 2.International Arctic Research CenterUniversity of Alaska FairbanksFairbanksUSA

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