Hess, M., P. Koepke, and I. Schult (1998)

Hess, M., P. Koepke, and I. Schult (1998): Optical Properties of Aerosols and Clouds: The software package OPAC, Bull. Am. Met. Soc., 79, 831-844. (PDF)


The software package OPAC (Optical Properties of Aerosols and Clouds) is described. It easily provides optical properties in the solar and terrestrial spectral range of atmospheric particulate matter. Microphysical and optical properties of 6 water clouds, three ice clouds and 10 aerosol components, which are considered as typical cases, are stored in ASCII files. The optical properties are the extinction, scattering and absorption coefficients, the single scattering albedo, the asymmetry parameter and the phase function. They are calculated on the basis of the microphysical data (size distribution and spectral refractive index) under the assumption of spherical particles in case of aerosols and cloud droplets and assuming hexagonal columns in case of cirrus cl ouds. Data are given for up to 61 wavelengths between 0.25 m and 40. m and up to 8 values of the relative humidity. The software package also allows calculation of derived optical properties like mass extinction coefficients and Angstrom coefficients.

Real aerosol in the atmosphere always is a mixture of different components. Thus, in OPAC it is made possible to get optical properties of any mixtures of the basic components and to calculate optical depths on the base of exponential aerosol height profile s. Typical mixtures of aerosol components as well as typical height profiles are proposed as default values; but mixtures and profiles for the description of individual cases may also simply be achieved.