Tracks in the Sky
~ Rare ice halo arcs criss-cross in a magnificent diamond dust display at Sollefteå northern Sweden. Images by Sofia Andersson on Nov 23,'15. There are at least 10 halos in this image alone. More below and in the previous OPOD.
All images ©Sofia Andersson, shown with permission
Subhelic arcs are more complicated. Singly oriented columns produce them. Sun rays enter an end face, reflect twice and exit through the other end face.
Helic arcs originate from external reflections from the side faces of Parry oriented crystals.
All the arcs labelled in the HaloSim ray tracing at right were visible.
The red polygon roughly outlines the area in the image above.
Helic, Wegener, supralateral and 46° arcs almost intersect. Below that a bright subhelic arc crosses a rare parry supralateral arc. At right blaze Parry and upper tangent arcs.