Evaluation of cloud-radiation sensitivities to alternative cloud and convection schemes

We have developed a single-column model (SCM) to investigate the sensitivity of cloud-radiation interactions to the choice of cloud and cumulus convection parameterizations. The SCM is a diagnostic model resembling a single vertical column of a 3-dimensional general circulation model (GCM). The SCM includes physical parameterizations that are currently used in modern GCMs. Due to the one-dimensionality of the SCM, the horizontal advection of heat, moisture and momentum are supplied to the model from either observations or 3-dimensional numerical analyses. The SCM results presented in this paper were produced using horizontal advective terms derived from observations taken at the Atmospheric Radiation Measurement (ARM) Program's Southern Great Plains (SGP) site.

Model results from the SCM control simulation compare reasonably well with the ARM SGP observations. The sensitivity of the modeled cloud fields and the surface and TOA radiative flux budget to various cloud parameterizations will be examined. The cloud parameterizations differ with regard to the inclusion of cloud liquid water as an interactive variable, the specification of the effective cloud droplet radius, and the parameterization of the cloud optical properties (both solar and terrestrial). During periods of convective activity, the experiments are carried out using alternative cumulus convection parameterizations. The effect of the cumulus parameterization on the modeled cloud fields and the radiative flux budget will also be discussed.