Solar radiative transfer for stratiform clouds with horizontal variations in liquid-water path and droplet effective radius

Effects of horizontal variations in liquid-water path (LWP) and droplet effective radius (r(e)) on solar radiative-transfer properties of stratiform clouds are addressed. To this end, a broadband Monte Carlo solar radiation code and in situ aircraft observations of cloud properties collected in the Radiation, Aerosol and Cloud Experiment are used. The experiments confirm that the radiative impact of cloud horizontal inhomogeneity is dominated by variations in LWP, which make cloud short-wave albedo smaller than that for a corresponding plane-parallel horizontally homogeneous cloud. When horizontal variations in r(e) are accounted for, however, the impact due to horizontal variations in LWP is usually reduced. When r(e) and LWP are highly correlated, as is typically the case, the impact on albedo due to LWP variations alone can be reduced easily by 30% when variations in re are included. Uncertainty factors involved in the calculations are also discussed.