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    Original Research Papers

    Cloud variability, radiative forcing and meridional temperature gradients in a general circulation model

    Authors:

    Peter L. Langen ,

    Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, Copenhagen, DK
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    Rodrigo Caballero

    Meteorology and Climate Center, University College Dublin, Dublin, IE
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    Abstract

    Due to the non-linearity of cloud—radiation interaction in general circulation models (GCMs), the time-mean cloud radiative forcing (CRF) is in general different from the CRF of time-mean clouds. This implies that a change in temporal cloud variability induces a change in radiative forcing even if there is no change in time-mean cloud properties. Here we investigate this variability contribution to CRF quantitatively in the National Center for Atmospheric Research Community Climate Model 3.6 GCM. In a reference run, the variability contribution is found to account for 35% of the global-mean climatological CRF. The variability contribution peaks in the mid-latitudes and is shown to be driven by synoptic eddy activity. In a climate change experiment, where the atmospheric CO2 is quadrupled, the change in cloud variability offsets 40% of the change in CRF due to the change in mean clouds. It is found that almost all of this effect is due to variability in cloud fraction rather than in cloud water content, and it is traced to the non-linearity introduced by the model’s treatment of vertical cloud overlap. This study indicates the possibility of an eddy variability-climate feedback that has not been extensively studied and quantified in the past.

    How to Cite: Langen, P.L. and Caballero, R., 2007. Cloud variability, radiative forcing and meridional temperature gradients in a general circulation model. Tellus A: Dynamic Meteorology and Oceanography, 59(5), pp.641–649. DOI: http://doi.org/10.1111/j.1600-0870.2007.00265.x
      Published on 01 Jan 2007
    Peer Reviewed
     CC BY 4.0
     Accepted on 25 May 2007            Submitted on 6 Nov 2006

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