Two- and four-stream optical properties for water clouds and solar wavelengths

Presented is a parameterization of the liquid water droplet optical properties for the solar spectrum. Two models are provided: a 4-band model for use in general circulation models and a 31-band model for use in higher spectral resolution investigations. The form of the parameterization is a simple extension of Slingo [1989], and the subdivision of wavelengths into bands is almost identical. The parameterization scheme is for all of the optical properties needed to perform 2- and 4-stream calculations. The 4-band model has the same spectral divisions as Slingo [1989], whereas the 31-band model has finer resolution of the absorbing bands in the near infrared. The parameterized single-scattering optical properties are accurate to within 0.5% compared to exact Mie calculations for both band models over the reff range from 5 to 40 μm. The layer radiative properties, from both two- and four-stream methods, are almost always within 1% accuracy compared to calculations using exact optical properties as inputs. Also, it is shown that using the Henyey-Greenstein phase function to obtain the higher-order moments, used in four-stream calculations, results in substantial error in the layer radiative properties compared to using exact Mie inputs.