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Abstract

An uncertain representation of convective clouds has emerged as one of
the key barriers to our understanding of climate sensitivity. The large
gap in resolved spatial scales between General Circulation Models (GCMs)
and high resolution models has made a systematic study of convective
clouds across model configurations difficult. It is shown here that the
simulated atmosphere of a GCM in Radiative Convective Equilibrium (RCE)
is sufficiently similar across a range of domain sizes to justify the
use of RCE to study both a GCM and a high resolution model on the same
domain with the goal of improved constraints on the parameterized
clouds. Simulations of RCE with parameterized convection have been
analyzed on domains with areas spanning more than two orders of
magnitude (0.80-204x10(6)km(2)), all having the same grid spacing of
13km. The simulated climates on different domains are qualitatively
similar in their degree of convective organization, the precipitation
rates, and the vertical structure of the clouds and water vapor, with
the similarity increasing as the domain size increases. Sea surface
temperature perturbation experiments are used to estimate the climate
feedback parameter for the differently configured experiments, and the
cloud radiative effect is computed to examine the role which clouds play
in the response. Despite the similar climate states between the domains
the feedback parameter varies by more than a factor of two; the
hydrological sensitivity parameter is better behaved, varying by a
factor of 1.4. The sensitivity of the climate feedback parameter to
domain size is related foremost to a nonsystematic response of low-level
clouds as well as an increasingly negative longwave feedback on larger
domains.