Infralateral arc (or lower lateral tangent arc)

(Section 3.2.3.1.10)

This is a rare pair of coloured arcs just outside and tangential to the 46° halo, and is always found below the level of the parhelic circle. The shape changes with the elevation of the light source. With increasing Sun elevation, the contact points at the 46° halo move downward along the 46° halo. Later, the infralateral arcs form a common arc. At a Sun elevation of 68°, this arc touches the 46° halo vertically below the Sun. When the Sun gets still higher, the vertex of the arc lies some degrees below the 46° halo. An infralateral arc can be as bright and colourful as a circumzenithal arc.