Atmospheric
Optics
Circumscribed Halo
Imaged by Marion Glas during the recent intense halo display over The Netherlands.
The inner circular halo is the familiar 22° halo. A faint parhelic circle cuts across it and the sun.
The outer baggy halo is the circumscribed. It is tangent to the 22° halo directly above and below the sun
Image ©Marion Glas
At sunrise there are symmetrical upper and lower tangent arcs. As the sun climbs the upper one's wings increasingly droop low over the 22° halo.
Come 29° and the tangent arcs fuse into the circumscribed halo. It tightens around the 22° halo and at high sun the two can be hard to distinguish.
Singly oriented column crystals make it.
