Swedish Ice Halos
Juha Kangas imaged this unusual display on November 25, '12 at Åre, Sweden.

©Juha Kangas, shown with permission

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Horizontal column crystals, Parry crystals and some as yet unidentified ones dominate this display.

Sunlight refracted through horizontal hexagonal columns of ice produced the blindingly bright "gulls wings" upper tangent arc. Above it another V shaped halo - a sunvex Parry arc.

The third 'V' below the upper tangent arc and inside the 22° halo is the mysterious Moilanen arc and this is perhaps one of the finest images of it.

The ice crystals responsible for Moilanen arc formation are not known. It can be simulated - as below - by tracing rays through a prism with two faces inclined 34° to each other. Single ice crystals do not possess such an angle, it is crystallographically highly improbable. Possibly the 34° occurs in some kind of crystal cluster but there is no evidence yet from crystal samples. The sharpness of the arc suggests precise crystal orientation and that argues against complex cluster crystals.

The 34° wedge that produces the Moilanen arc.