title: Influence of crystal tilt on solar irradiance of cirrus clouds.
abstract: The single and multiple scattering and absorption properties of hexagonal ice columns with different degrees of particle orientation are modeled in the solar spectral range by means of a ray-tracing single-scattering code and a Monte Carlo radiative-transfer code. The scattering properties are most sensitive to particle orientation for the solar zenith angles of 50 degrees (asymmetry parameter) and 90 degrees (single-scattering albedo). Provided that the ice columns are horizontally oriented, the usual assumption of random orientation leads to an overestimation (underestimation) of the reflected (transmitted) solar broadband radiation at high Sun elevation and to an underestimation (overestimation) at medium solar zenith angles. The orientation effect is more (less) pronounced in scattering and transmission (absorption) for smaller ice crystals.
authors.affiliation: Max Planck Institute for Meteorology, Bundesstrasse 55, 20146 Hamburg, Germany. klotzsche@dkrz.de
authors.forename: Susann
authors.initials: S
authors.lastname: Klotzsche
authors.forename: Andreas
authors.initials: A
authors.lastname: Macke