Technical Note: Optical properties of desert dust with non-spherical particles: data incorporated to OPAC

Abstract

Abstract. Mineral desert dust particles in general are no spheres and assuming spherical particles, instead of more realistic shapes, has significant effects on modeled optical dust properties and so on the belonging remote sensing procedures for desert dust and the derived radiative forcing. Thus in a new version of the data base OPAC (Optical Properties of Aerosols and Clouds; Hess et al., 1998), the optical properties of the mineral particles are modeled describing the particles as spheroids with size dependent aspect ratio distributions, but with the size distributions and the spectral refractive indices not changed against the previous version of OPAC. The spheroid assumption strongly improves the scattering functions, but pays regard to the limited knowledge on particle shapes in an actual case. The relative deviations of the phase functions of non-spherical mineral particles from those of spherical particles are up to +60% at scattering angles of about 130° and up to −60% in the backscatter region, but the deviations are generally small for optical properties that are independent of the scattering angle. The improved version of OPAC (4.0) is freely available under