Cirrus castellanus
Ci cas
Cirrus castellanus
© Wetterkurs.ch
Description
The name "castellanus" (Latin: castle-like, from castellum = small castle) describes the tower- or battlement-like protrusions that rise from a common base. Cirrus castellanus appears as a high, delicate ice cloud with clearly visible vertical, turret-shaped upward bulges. These convective forms develop through local convective instability at great altitude, typically above 6,000 metres. In contrast to ordinary cirrus, which tends to appear fibrous and horizontally spread, Cirrus castellanus displays distinct vertical structures reminiscent of the battlements of a medieval castle. The cloud consists entirely of ice crystals and can produce fall streaks (virga) under suitable conditions.
Identification Features
- Turret- or battlement-shaped vertical upward bulges rising from a common, often narrow base
- Located at great altitude (typically above 6,000 m), therefore appearing white and delicate
- Vertical extent of the turrets is greater than their width
- Composed of ice crystals, therefore appearing partly fibrous at the edges
- Frequently associated with fall streaks (virga) at the base
- Distinguished from flat cirrus by its pronounced vertical development
- Often occurs in rows or bands, with the turrets resembling a castle wall
- Can easily be confused with Cirrocumulus castellanus, but has less regular individual elements
Occurrence by genus
Highlighted: all genera with which castellanus occurs.
Meteorological Significance
Cirrus castellanus is an important indicator of instability in the upper troposphere. The presence of convective upward bulges at this altitude points to moisture and unstable stratification, which can be interpreted as a precursor to the development of thunderstorms in the following 12 to 36 hours. Observed particularly in the morning, Cirrus castellanus is considered one of the most reliable early warning signs of summertime convective development. It indicates that the atmosphere in the middle and upper layers possesses sufficient energy and moisture for the formation of cumulonimbus clouds. In combination with other signs of instability, such as Altocumulus castellanus, the likelihood of impending shower or thunderstorm activity increases considerably.
Facts
- WMO-Code
- Ci cas
- Height layer
- High clouds
- Typical height
- 6.0 - 12.0 km
- Genus
- CIRRUS