Ac compared with Ci
(Section 2.3.4.6.1)Altocumulus is distinguished from Cirrus by:
- Absence of a mainly fibrous or silky appearance
- Presence of cloud elements in the form of laminae, rolls, etc
- Possible shading throughout that never occurs with Cirrus
- Usually being partly shaded, compared to Cirrus, which does not usually have shading
- Possibility of cloud elements arranged in undulations
- Possible virga
- Usual presence of a corona
Altocumulus sometimes produces descending trails of fibrous appearance (ice crystal virga). The cloud is identified as Altocumulus and not as Cirrus, as long as the cloud has a part without a fibrous appearance or a silky sheen.