How to differentiate the circumhorizon arc from the infralateral arc?
At a solar height > 60°, the two lateral infralateral arcs combine into a lower arc, which is very difficult to distinguish from the circumhorizontal arc when only a lower fragment is present. The following distinguishing features aid in identification.
Circumhorizontal Arc
- Halo is often brightly colored and frequently wide and diffuse
- Arc runs parallel to the horizon
- is most often seen in individual cirrus clouds
Infralateral arch
- Bow is narrower and clearly defined
- runs slightly V-shaped upward directly from the apex below the sun
- is more often seen in homogeneous cirrostratus
- Circumscribed halo is present and the 22° ring is not visible or significantly weaker than the circumscribed halo
The top two photos show the circumhorizontal arc and the right part of the infralateral arc. The picture was taken on 28.06.2014 by Alexander Haußmann in Dresden. To enhance the halo types, the photos were edited using the USM method.