Albedo Feedback, the Meridional Structure of the Effective Heat Diffusivity, and Climatic Sensitivity: Results from Dynamic and Diffusive Models

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  • 1 Geophysical Fluid Dynamics Laboratory/N0AA, Princeton University, Princeton, NJ 08540
  • 2 Department of Atmospheric Sciences, University of California, Los Angeles 90024
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Abstract

The sensitivity of a two-level primitive equation atmospheric model to solar constant perturbations is examined in the presence of surface albedo feedback. The model is simplified to the point that a large number of numerical experiments can be performed and statistically steady states defined with relative case. Exceptionally sensitive equilibrium states are found that are unrelated to the large and small ice-cap instabilities obtained in the simplest diffusive energy balance models. Similar results are produced in a two-level diffusive model closely patterned after the dynamic model, and in a more highly idealized one-level model, by choosing a diffusivity with pronounced meridional structure resembling that of the effective diffusivity of the dynamic model. Sensitive states occur in the diffusive models when the albedo gradient enters the region equatorward of 60° in which the effective heat diffusivity of the atmosphere increases with increasing latitude.

Abstract

The sensitivity of a two-level primitive equation atmospheric model to solar constant perturbations is examined in the presence of surface albedo feedback. The model is simplified to the point that a large number of numerical experiments can be performed and statistically steady states defined with relative case. Exceptionally sensitive equilibrium states are found that are unrelated to the large and small ice-cap instabilities obtained in the simplest diffusive energy balance models. Similar results are produced in a two-level diffusive model closely patterned after the dynamic model, and in a more highly idealized one-level model, by choosing a diffusivity with pronounced meridional structure resembling that of the effective diffusivity of the dynamic model. Sensitive states occur in the diffusive models when the albedo gradient enters the region equatorward of 60° in which the effective heat diffusivity of the atmosphere increases with increasing latitude.

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