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

Presented is a parameterization of the liquid water droplet optical propert ies 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 spectr al resolution investigations. The form of the parameterization is a simple extension of Slingo [1989], and the subdivision of wavelengths into bands i s almost identical. The parameterization scheme is for all of the optical p roperties 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 para meterized single-scattering optical properties are accurate to within 0.5% compared to exact Mie calculations for both band models over the r(eff) ran ge from 5 to 40 mu m. The layer radiative properties, from both two- and fo ur-stream methods, are almost always within 1% accuracy compared to calcula tions using exact optical properties as inputs. Also, it is shown that usin g 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.