Halos - Imaged by Franck Schwitter at 2000m plus in Crans Montana, Switzerland.
Diamond dust, ice crystals glinting and swirling all around in the cold air, produces some of the very finest displays. Those seen near ski resorts are often artificial, produced by wind-blown crystals from snow machines. These halos were fully natural as no machines were operating.
The lower circle is a 22 degree halo topped by a "gull's wing" upper tangent arc made by horizontal column crystals. The same crystals made the large downward curving arc at top - a supralateral arc. Touching the supralateral and curving upwards is a brightly coloured circumzenithal arc made in this display by plate crystals.
Supralateral and circumzenithal arcs are broader with more apparent colour because the rays forming them pass between crystal faces tilted 90° to each other. Compared to the smaller 60° face inclination of sundog and 22 degree rays, the colours are spread wider apart in the sky.
Image ©Franck Schwitter, shown with permission.