The formation mechanism of elliptical halos and Bottlinger’s rings has long remained uncertain. The current model for elliptical halos requires multiple scattering from two different populations of ice crystals in a complex mode of motion. New evidence indicates that elliptical halos, and possibly Bottlinger’s rings, are due to refraction through ice crystals shaped like obtuse pyramids. This unusual ice crystal may not have been documented previously.
© 1999 Optical Society of America
Mika Sillanpää, Jarmo Moilanen, Marko Pekkola, Martti Penttinen, and Jari Piikki, "Unusual Pyramidal Ice in the Atmosphere as the Origin of Elliptical Halos," Appl. Opt. 38, 5089-5095 (1999)