Circumscribed halo

From Glossary of Meteorology

circumscribed halo

The descriptive name given to the fully developed 22° tangent arcs for light- source elevation angles of between approximately 30° and 75°.

At these elevation angles, the upper and lower 22° tangent arcs merge to form a kidney-bean- shaped halo circumscribing the halo of 22°. Sometimes the term "circumscribed halo" is misleadingly employed as equivalent to the 22° tangent arcs.