Scattering of Polarized Laser Light by Water Droplet, Mixed-Phase and Ice Crystal Clouds. Part I: Angular Scattering Patterns

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  • 1 Department of Meteorology, University of Utah, Salt Lake City 84112
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Abstract

Laboratory studies of the angular scattering and depolarizing behavior of water, ice and mixed-phase clouds are described in Parts I and II of this report. In Part I, we present the theoretical background and experimental apparatus for determining the angular scattering pattern in the laboratory. The experimental results obtained with vertically and horizontally polarized laser light (0.6328 μm) are given in the form of normalized scattering phase functions to facilitate their comparison to theoretical predictions. Close agreement between Mie theory and experiment is found for water clouds when the measured cloud droplet size distribution is input into the computations. For ice crystal clouds containing small (<50 μm), randomly oriented particles, the agreement with theory using either the spherical or long cylinder shape approximation is less noteworthy due to the presence of more intense side-scattering and the absence of cloudbows in the experimental ice data. The scattering behavior of mixed-phase clouds, an important group of atmospheric clouds, is shown to be highly sensitive to the differences in the relative scattering efficiencies of the water and ice particles as a function of the scattering angle. Also considered are the effects of ice crystal size and shape on the angular scattering patterns. Finally, normalized phase function values for a representative ice crystal cloud are presented in tabulated form.

Abstract

Laboratory studies of the angular scattering and depolarizing behavior of water, ice and mixed-phase clouds are described in Parts I and II of this report. In Part I, we present the theoretical background and experimental apparatus for determining the angular scattering pattern in the laboratory. The experimental results obtained with vertically and horizontally polarized laser light (0.6328 μm) are given in the form of normalized scattering phase functions to facilitate their comparison to theoretical predictions. Close agreement between Mie theory and experiment is found for water clouds when the measured cloud droplet size distribution is input into the computations. For ice crystal clouds containing small (<50 μm), randomly oriented particles, the agreement with theory using either the spherical or long cylinder shape approximation is less noteworthy due to the presence of more intense side-scattering and the absence of cloudbows in the experimental ice data. The scattering behavior of mixed-phase clouds, an important group of atmospheric clouds, is shown to be highly sensitive to the differences in the relative scattering efficiencies of the water and ice particles as a function of the scattering angle. Also considered are the effects of ice crystal size and shape on the angular scattering patterns. Finally, normalized phase function values for a representative ice crystal cloud are presented in tabulated form.

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