Group Cirrus.
Under the general head of cirrus we have found nine distinct forms—
1. Cirro-nebula (Ley) (Plates [2] and [3]). Cirrus veil.
Characterized by comparative absence of structure and by the formation of halo. Ci. Na.
2. Cirro-filum (Ley) (Plate [7]). Thread cirrus.
Built up of fine long threads, straight, curved, or crossing, but free from hazy curling or flocculent structures. Ci. F.
3. Cirrus excelsus (Plate [5]). High cirrus.
Characterized by great altitude, thinness, irregular branching structure. Ci. Ex.
4. Cirrus ventosus (Plate [6]). Windy cirrus.
Characterized by curving branches leaning forward in the direction of movement, and other long curving streamers lagging behind and below. Fluffy parts are usually present, and mark the origins of the long curling fibres. Ci. V.
5. Cirrus nebulosus (Plate [9]). Hazy cirrus.
Characterized by the absence of sharply defined lines, fibres, or streamers; all parts of the cloud being hazy, and suggestive of other varieties of cirrus out of focus. Ci. Neb.
6. Cirrus caudatus (Plate [8]). Tailed cirrus.
Characterized by small hazy or fluffy heads behind or below which hang long streamers, which taper away more or less to a point. The tails are sharply defined, and so are the edges of the heads. Ci. Ca.
7. Cirrus vittatus (Plates [12] and [13]). Ribbon cirrus.
Characterized by formation in long bands of cloud, sometimes made of parallel long fibres with cirrus haze linking them together, sometimes consisting of a long bundle of fibres, from which others diverge at an angle as shown in the plate. Ci. Vt.
8. Cirrus inconstans (Plate [10]). Change cirrus.
Characterized by a peculiar ragged, wavy appearance. It is generally only the beginning or the end of a mass of cirro-stratus or cirro-cumulus, but occasionally it vanishes shortly after its appearance, without reaching the further stage. Ci. In.
9. Cirrus communis (Plate [11]). Type cirrus or common cirrus.
Characterized by short irregularly curling fibres collected together in considerable patches. No definite arrangement into any of the forms already described. Ci. Com.