Klotzsche, Susann (2004) Einfluss der Kristallorientierungen auf die solaren Strahlungsflüsse von Cirruswolken. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 78 pp.

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Abstract

The present work describes the influence of the orientation of hexagonal ice crystals on its single scattering and on multiple scattering of solar radiation in cirrus clouds. Scattering phase function and single scattering albedo were calculated with a Ray-Tracing model, the radiance flux density and the radiance of ice clouds by means of a Monte-Carlo radiative transfer model. A total of 13 wavelenghts (0.2 μm > ,\ > 4.0 μm), 10 maximum tilt angles of the crystals around the horizontal axis, 5 crystal size distributions, 6 optical thickness (0.5 > T > 12.0) and 10 solar zenith angles 80 have been considered. The effect of particle orientation is strongest pronounced for Θ0 = 0° and Θ0 = 40°. For a typical optical thickness T = 2 and solar zenith angle of 40° the differences in the solar broadband fluxes are as large as 125.4 m-2 for reflected radiance flux density and as large as 129.9 wm-2 for the transmitted flux. The absorption is less affected by crystal orientation. For hexagonal plates these effects are smaller than for hexagonal columns. The radiance flux density is stronger influenced by crystal orientation for smaller crystals. This sensitivity can also be observed in the transmitted and the reflected radiance. As an application, the tilt angle can be infered from the shape of halo components. This work gives detailed geometrical explanations for the dependence of single and multiple scattering on crystal shape and orientation. The choice of crystal orientation has a similar effect on the radiative properties of cirrus clouds as crystal shape and size distribution.

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