Ci compared with Cs

(Section 2.3.1.6.2)

Cirrus is distinguished from Cirrostratus by:

• Discontinuous structure or, if they are in patches or bands, the small horizontal extent or the narrowness of their continuous parts
• Sometimes being thick enough to mask the Sun or Moon (Cirrostratus is always thin enough to show the disc of the Sun or Moon)
• Absence of undulations
• Possible mamma, usually in the species spissatus
• Absence of a corona
• Only having, at best, a partial circular halo

Cirrus near the horizon may be difficult to distinguish from Cirrostratus, owing to the effect of perspective.