The contribution of cloud inhomogeneities and droplet concentration to the albedo of broken‐cloud fields

Abstract

AbstractCloud fields from a Large‐Eddy Simulation (LES) combined with a Monte Carlo radiative‐transfer model have been used to examine the behaviour of clouds with regard to the monochromatic albedo of short‐wave solar radiation. the LES cloud fields have an inhomogeneous structure in two dimensions and contain highly irregular concentrations of liquid water. the calculations show that the albedo sensitivity to the cloud‐field orientation becomes notably important for solar zenith angles above 30° for the LES clouds used. Replacing each cloud point with the in‐cloud mean water content, increases the cloud‐field albedo, compared to the original cloud‐field albedo, in many cases by more than 30%. Calculations have also been made with differing droplet concentrations throughout the cloud fields. It is found that changes in the cloud‐field albedo with droplet concentration are influenced by the general degree of inhomogeneity in the cloud structure. the original irregular LES cloud fields are more sensitive to changes in the droplet concentration than their equivalent plane‐parallel clouds with the same total water content and mean vertical water‐content profiles.