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Supralateral Arcs

The supralateral arc touches the 46° halo at both sides and changes its shape according to solar elevation. It can also touch the circumzenithal arc. It is formed by columnar ice rcystals. Like the circumzenithal arc supralateral arcs only occur below a solar elevation of 32°.

Supralateral arcs are sometimes hard to distinguish from the 46° halo. One possible criterion is colour. Supralateral arcs are much brighter and much more colourful than the 46° halo, which is six times fainter than the 22° halo. The 46° halo never changes its shape. The supralateral arc is never totally circular. The 46° only touches the circumzenithal arc at solar elevations between 15 and 27°.

Supralateral arcs can only be found above the plane of the parhelic circle. Below, the equivalent arcs are called infralateral arcs. They are as colourful as the supralateral arc, but yet rarer in higher latitudes because of their proximity to the horizon. Infralateral arcs equally change their shape with solar elevation.

Simulation of infralateral arcs and the supralateral arc at a solar elevation of 22°. Crystal concentration must be extremely hight to produce such a display. The simulation also shows an upper and a lower tangent arc, the parhelic circle and some very rare halos. Simulation with HaloSim 3.6 by © Les Cowley and Mike Schroeder shown with permission.


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