No abstract

Abstract.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 $1ingo [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 $1ingo [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 tee range from 5 to 40 •m. 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.

Abstract. Recent studies indicate that interstellar grains are composites of very small individual particles of silicates and carbon glued together into an aggregate. Using the discrete dipole approximation (DDA), we calculate the extinction, scattering and absorption efficiencies for composite grains assumed to be made of a host silicate sphere with embedded graphite inclusions. In particular, we study the extinction as a function of inclusion size and volume fraction. Using the extinction efficiencies of these composite grains, we evaluate the interstellar extinction curve in the wavelength region of 0.55 µm−0.20 µm.

No abstract

Parameterizations of the shortwave optical properties of ammonium sulfate [(NH 4) 2 SO 4 ], ammonium bisulfate (NH 4 HSO 4), and sulfuric acid (H 2 SO 4) are provided as functions of relative humidity for high and low spectral resolution band models. The optical property parameterization is simple in form and in its dependence on relative humidity. The growth of the aerosol particles is based on equilibrium saturation theory, and the optical properties are computed from Mie theory. The optical properties necessary for the most commonly used radiative transfer methods are provided. Results show that when relative humidity effects are included in the backscatter fraction the radiative forcing is found to be a more sensitive function of near infrared wavelengths compared to visible wavelengths. For increasing relative humidity, sulfuric acid is found to have a larger effect on radiative forcing compared to the forcing by ammonium sulfate or ammonium bisulfate. Also, as relative humidity increases, forcing increases to higher values for smaller mode size distributions compared to forcing by larger mode distributions. These parameterizations will enable climate forcing studies to be performed with radiative transfer schemes that more accurately represent sulfate influences on the radiation balance.