Fraunhofer Diffraction by Ice Crystals Suspended in the Atmosphere

Fraunhofer diffraction has been explicitly formulated for a finite hexagonal cylinder and a spheroid in any arbitrary orientation. The diffracted intensity was computed for hexagonal cylinders and spheroids oriented randomly in a three dimensional space and in a horizontal plane. The diffraction by hexagonal cylinders in 3D random orientation can be well approximated by that of spheroids of the same aspect ratio. For horizontal orien-tation, the diffracted intensity is a function not only of the scattering angle but also of the azimuth angle, and the diffraction patterns for hexagonal cylinders and spheroids are quite different from each other. The diffraction patterns of hexagonal cylinders in horizontal orientation strongly depend on the source elevation, showing patterns highly anisotropic with respect to the azimuth angle at low source elevations. Applications to optical phenomena due to ice crystals in the atmosphere are also discussed. 1