We have developed a single-column model (SCM) to investigate the sensitivity of cloud-radiation interactions to the choice of cloud parameterization. The SCM is a diagnostic model resembling a single vertical column of a 3-dimensional general circulation model (GCM). The SCM includes physical parameterizations which 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 by the Atmospheric Radiation Measurement (ARM) Program.
Model results from a control simulation are first evaluated against
in situ observations taken at the ARM Southern Great Plains (SGP) site. Model shortwave and longwave radiative fluxes, cloud amount, and precipitation are compared to both surface and satellite measurements. Additionally, the vertical profile of model-produced cloud amounts and optical thicknesses are analyzed using available observations from the
ARM SGP site. These results from the SCM control simulation compare reasonably well with the ARM SGP observations. A significant improvement (compared to ARM observations) in the SCM radiative fluxes and cloud amount is noted when the model temperature and
humidity profiles are relaxed towards observed profiles.
The SCM is then used to determine the sensitivity of the surface and TOA radiative flux budget to various cloud parameterizations. 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). Preliminary results show that various components of the surface and TOA radiative budget are sensitive to both the inclusion of cloud liquid water and the method used to specify the effective cloud droplet