Dr. Christopher M. Godfrey Atmospheric Halos University of North Carolina at Asheville Columnar and Plate Ice Crystals Complex Display at South Pole Image © Marko Riikonen ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 Good/Bad Crystals for Halo Formation 22° and 46° Halos Crystals collected during a superb Crystals from a mediocre halo South Pole display on 17 January display 16 days earlier. They have 1986. Apart from a few small air large inclusions and their faces are bubble inclusions, the crystals imperfect. (Photographs from really are like their hexagonal plate Atmospheric Halos by Walter Tape) and column ideals. Source: http://www.atoptics.co.uk/halo/xtalreal.htm ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 22º Halo Sundog (Parhelion) © S. Hudson ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 1 Ice Crystal Phenomena Halos and Sundog 22º Halo 46º Halo Parhelic Circle Sundog © S. Hudson ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 © C. Godfrey 22º Halo and Sundogs Sundog 22º Halo (parhelion) Parhelic Circle Sun Sundog Sundog © S. Hudson ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 © E. Godfrey 22º Halo Upper Tangent Arc Parhelic Parhelic Circle Circle Positioned at top of 22° halo Diamond dust was falling when the photo was taken Sun Sundog (parhelion) © C. Godfrey ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 2 Circumzenithal Arc Upper Tangent Arc with Circumzenithal Arc Circumzenithal Arc You are looking almost straight up with the sun at the bottom of the image Formed by refraction through hexagonal plate crystals Supralateral Arc The supralateral arc is more common than, and is often 22º Halo mistaken for, the 46° halo Sun is below 32° elevation © C. Godfrey © S. Hudson ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 Sundog, parhelic circle, 22° halo, and a dim More information upper tangent arc Image © Jim Hoida (http://apod.nasa.gov/apod/ap060923.html) For more great images and explanations, visit © C. Godfrey http://www.atoptics.co.uk/halosim.htm ATMS 455: Physical Meteorology – Spring 2021 ATMS 455: Physical Meteorology – Spring 2021 3.