Climate Dynamics

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Revealing differences in GCM representations of low clouds

Brian Medeiros & Bjorn Stevens


Aquaplanet configurations of four atmospheric general circulation models are compared with standard, Earth-like configurations and observations. The focus here is on tropical, low-level clouds, which have been identified as important for estimates of climate sensitivity. Investigating the distribution of the monthly mean vertical velocity and lower-tropospheric stability, the aquaplanets are seen to capture the core of the distribution of the more Earth-like configurations, whose distributions are, in turn, similar to that of reanalysis data. By conditionally sampling over these distributions, low-cloud regimes are defined, separating shallow cumulus convection from stratocumulus. Within each regime, the GCMs produce similar large-scale environments, yet disparate depictions of the clouds. Aquaplanets lack stratocumulus because of their zonally symmetric boundary conditions, but produce extensive trade-wind regions populated by shallow cumulus clouds just like those in the Earth-like setting. The analysis shows that aquaplanets can be compared with observations, just as well as the Earth-like configuration, with the added ability to focus on particular regimes without complications from geographical or temporal biases.

This paper was published Open Access and "Online First," appearing on the Climate Dynamics web site on 8 November 2009. It appeared in print in January 2011. I think the proper citation is:
B. Medeiros and B. Stevens, “Revealing differences in GCM representations of low clouds,” Climate Dynamics, vol. 36, no. 1, pp. 385–399, 2011. doi:10.1007/s00382-009-0694-5.