Supralateral arc

EE 21

Crystal orientation:
main axes horizontal
Path of light:
3-2 / 3-1
ca. once in a year
Picture supralateral arc
The supralateral arc dominates the picture. Below of the parhelic arc the
infralateral arc is visible too. There is also a upper tangent arc.
Photo: Dipl.-Ing. Inge Fuhrberg, Saalbach/Hinterglemm, 01/31/96


A supralateral arc changes its appearance subject to the sun elevation. When the sun is lower than 15°, the supralateral arc touches the 46°-halo at its sides. When the sun is on the horizon, the contact points to the 46°-halo are at the same elevation like the sun. At sun elevations between 15 and 27 the supralateral arc almost overlaps with the 46°-halo, so that they are very difficult to be distinguished. In fact a lot of observations of the 46°-halo seem to have really been observations of the supralateral arc. Only at sun elevations between 27° and 32° the supralateral arc is significantly higher in the sky than the 46°-halo. A circumzenithal arc can also give a hint how to distinguish the supralateral arc from the 46°-halo, as it touches the supralateral arc at all sun elevations. At sun elevations between 15° and 27°, however, this is also valid for the 46°-halo. Another possibility how to distinguish the two halos from one another can he provided by the greater colourfulness of the supralateral arc. In most cases the 46°-halo is just white or has a faint reddish inner rim. The supralateral arc, however, is much more colourful. Blue and green are also visible well. It can even become as colourful and bright as a rainbow.

The diagram shows a computer simulation of the supralateral arc and of the infralateral arc at different sun elevations for a better orientation the 46°-halo, the 22°-halo and the parhelic circle are also drawn in. The supralateral arc is the arc which touches the 46°-halo at its sides and at its upper part. At sun elevations of more than 32° the supralateral arc cannot form. Thus, the diagram only shows the infralateral arc for sun elevations of 40° and more. The infralateral arc touches the 46°-halo at its lower side parts. Diagram taken from: R. Greenler; Rainbows, Halos and Glories; Cambridge University Press, 1980.


A supralateral arc is caused by column-shaped ice crystals which are floating in the air. The light enters the vertical base face of the crystal and leaves a prism face. As the tangent arcs to the 22°-halo are also caused by column-shaped ice crystals, the appearing of a bright tanqent arc may be a hint for the arc above the 22°-halo being a supralateral arc and not a 46°-halo.

Characteristics of 46°-halo and supralateral arc

Halos visible 46°-halo Supralateral arc 46°-halo and supralateral arc
Common properties
These features normally are appropriate to identify the halo in the 46°-region. If the halo still cannot be determined exactly by these properties, then also check the criteria for the corresponding sun elevation
  • Halo is poorly coloured (in most cases just red, orange and white are visible)
  • No tangent arcs to the 22°-halo visible, or they are significantly fainter than the 22°-halo
  • No infralateral arc visible
  • Halo is colourful (blue and green are also visible)
  • Tangent arcs are visible, but no 22°-halo, or 22°-halo is very much fainter than the tangent arcs
  • Supralateral arc always touches the circumzenithal arc (Keep in mind that at sun elevations between 15° and 27° also the 46°-halo touches the CZA)
  • Infralateral arc is visible
  • 22°-halo and tangent arcs are of similar brightness or both are well recognizable
  • Halo in the 46°-region has two sections which are significantly different; colourful and colourless or brighter and fainter parts
  • Good displays show up both halos simultaneously
  • Infralateral arc may be visible
Sun elevation less than 15°
Supralateral arc touches 46°-halo at its sides. If the sun is near the horizon, contact arcs are at the same elevation like the sun.
  • Gap between 46°-halo and circumzenithal arc
  • Only the upper part of the halo is visible
  • Halo is visible at both sides only, but symmetrically
  • Very colourful or bright section at both sides of the 46°-halo
Sun elevation between 15° and 27°
Identification of both halos results difficult as both halos overlap
  • Touches circumzenithal arc
  • Touches circumzenithal arc
  • Halos are very similar to each other; use also “Common properties”
Sonnenhöhe 27 bis 32°
Halos don't touch themselve.
  • Gap between 46°-halo and circumzenithal arc
  • Distance from sun is more than 46°
  • Bright and colourful section of a halo above 46°-halo
  • Two separate halos can be distinguished well
Sun elevation more than 32°
Supralateral arc does not exist at sun elevations of more than 32°
  • Halo in 46°-region is always a 46°-halo
  • Not possible
  • Not possible