Infralateral tangent arcs
From AMS Glossary
Reference: Tape, W., 1994: Atmospheric Halos. Antarctic Research Series, Vol. 64, Amer. Geophys. Union, 144 pp.
Two or one colored ice halo arcs approximately 46° below the sun.These arcs are produced by refraction of rays passing through hexagonal columnar ice crystals, the principal axes of which are horizontal but randomly directed in azimuth. Rays enter a near-vertical basal face and leave through a prism face (90° effective prism angle). Rays passing in the opposite direction can form a supralateral arc.
(term edited 5 Oct 2015)