Climate Change and Cloud Feedback: The Possible Radiative Effects of Latitudinal Redistribution

Gerald L. Potter Lawrence Livermore Laboratory, University of California, Livermore, CA 94550

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Huch W. Ellsaesser Lawrence Livermore Laboratory, University of California, Livermore, CA 94550

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Michael C. MacCracken Lawrence Livermore Laboratory, University of California, Livermore, CA 94550

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Connee S. Mitchell Lawrence Livermore Laboratory, University of California, Livermore, CA 94550

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Abstract

The sensitivity of outgoing longwave flux to changes in cloud cover (∂F/∂Ac) as defined by Cess (1976) must be evaluated carefully to avoid discrepancies arising from the interchange of averaging conventions. In a recent zonal atmospheric model experiment the global value of ∂F/∂Ac was different in sign than in other calculations. This difference in behavior was traced to a latitudinal redistribution of cloud amount and height that occurred in the doubled CO2 experiment. However, when ∂F/∂Ac was evaluated at individual latitudes and then weighted globally, the value of this parameter was consistent with those found by Cess (1976) and Budyko (1974).

Abstract

The sensitivity of outgoing longwave flux to changes in cloud cover (∂F/∂Ac) as defined by Cess (1976) must be evaluated carefully to avoid discrepancies arising from the interchange of averaging conventions. In a recent zonal atmospheric model experiment the global value of ∂F/∂Ac was different in sign than in other calculations. This difference in behavior was traced to a latitudinal redistribution of cloud amount and height that occurred in the doubled CO2 experiment. However, when ∂F/∂Ac was evaluated at individual latitudes and then weighted globally, the value of this parameter was consistent with those found by Cess (1976) and Budyko (1974).

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