The 46° Halo and Its Arcs
Robert G. Greenler 1,
James R. Mueller 2,
Werner Hahn 3, and
A. James Mallmann 4
1 Professor of physics at the University of Wisconsin-Milwaukee, Milwaukee 53201
2 Graduate student in applied mathematics at the California Institute of Technology, Pasadena 91109
3 IBM Corporation, Rochester, Minnesota 55901
4 Associate professor of physics at the Milwaukee School of Engineering, Milwaukee 53201
Ice crystals in the form of right hexagonal prisms have faces that form 90° prisms. Light rays were traced through these prism faces by computer calculation, and the light patterns that would be produced in the sky for a particular distribution of crystal orientations were simulated. Crystals with random orientations produce a 46° halo. Hexagonal plate crystals with nearly horizontal end faces produce circumzenithal and circumhorizontal arcs. Hexagonal column crystals with horizontal axes produce supralateral and infralateral arcs. Plate crystals spinning about a horizontal axis that is a face diagonal of the crystal produce a series of arcs touching the 46° halo. Each of these effects was simulated for several elevations of the sun.
