Aerial Halos &
|A 46° halo or infralateral arc at bottom left.|
|The sun elevation was about 25° and the angle of the cross at the antisolar (sub anthelic) point is consistent with Parry oriented columns forming an antisolar arc.
The halos around the sun show that randomly oriented crystals and singly oriented columns were also present. Crystals and halos were changing very quickly as the jet went through the ice crystal layer.
Much more on antisolar arcs here and here.
|Just 4 seconds earlier the glory was bright with a complete first ring and distorted partial second ring.|
The brightness variation along the subparhelic circle and the bright sub 120° parhelia suggest the presence of plate crystals with a triangular aspect, i.e. alternate vertical faces long and short.
|Glories are formed by water droplets rather than ice crystals. Supercooled water droplets can exist at 26,000 feet but they are not in equilibrium with ice crystals and cannot long co-exist. The droplets have a higher vapour pressure and evaporate with the moisture condensing as ice.
The glory is therefore puzzling. It could be formed by droplets in a lower cloud layer. Far less probable are ice spheres. The latter are never likely to be sufficiently smooth to allow the surface waves necessary for glory formation.
A thanks to Philip Laven for comments on glory formation by ice.
|The subparhelic circle. At far left a cross formed by the Parry antisolar arc. The aircraft shadow tells that the halo forming layer was not far below the airplane and that the photo was taken from its nose. A very faint glory colours the antisolar point. At right is a rare 120° subparhelion.|