23°-parryform arcs (EE69)

The upper 23° parry arc is a concave arc that sits like a hat on the 23° ring . It can only form at a sun elevation of about 15°. Between a sun elevation of 30° and 55°, the upper 23° parry arc is most intense. As the sun elevation increases, the arc dissolves. The lower 23° parry arc is visible only from a sun elevation of about 47°. In general, the 23° parry arcs do not touch the 23° ring. The upper arc touches it at a sun elevation of about 47.6°. In the scientific literature these arcs are called 23° plate arcs.