Uncertainty of SW Cloud Radiative Effect in Atmospheric Models Due to the Parameterization of Liquid Cloud Optical Properties

Clouds are largely responsible for the spread of climate models predictions. Here we focus on uncertainties in cloud shortwave radiative effect due to parameterization liquid single scattering properties (SSPs) from water content (LWC) and droplet number concentration (N), named optical properties. Uncertainties arise not accounting size distribution (DSD)—which affects estimation effective radius (reff) modulates reff-dependency SSPs—and averaging SSPs over wide spectral bands. To assess these a series reff-dependent parameterizations corresponding various DSDs methods derived implemented code. Combined with DSD-dependent reff they used compute bulk (reflectance, transmittance, absorptance) clouds (defined terms LWC N), including homogeneous cloud, more realistic case studies, outputs model. The results show that forcing can vary up 20% depending assumed DSD. Likewise, differences obtained heating rates. is main source uncertainty, while contributes around total uncertainty. Spectral less an issue, except atmospheric absorption. Overall, global by 6 W m−2 DSD shape, which about 13% best observational estimate.