Cirrus
Ci
Cirrus
© Wetterkurs.ch
Description
Cirrus (lat. curl of hair, tuft of feathers) is a high cloud genus consisting of fine, white threads, streaks, or narrow bands. These delicate clouds are composed exclusively of ice crystals and often appear in the sky like faint brushstrokes. Cirrus clouds typically form at altitudes between 6,000 and 12,000 metres, where temperatures are well below freezing. Due to their thin, transparent structure, they allow sunlight to pass through largely unimpeded and cast no appreciable shadow on the Earth's surface. They are among the most frequently observed clouds and occur worldwide in all climate zones.
Identification Features
- Delicate, fibrous, or hair-like structure in the sky
- Pure white colouring, often with a silky sheen
- Located at high altitude, clearly above other cloud layers
- Composed exclusively of ice crystals
- Appear as fine streaks, tufts, or hook-shaped formations
- Cast no shadow on the ground
- Allow the blue sky to show through clearly
- Can be shaped by strong upper-level winds into long, drawn-out bands
Species of this genus
Highlighted: all species that occur with Cirrus.
Meteorological Significance
Cirrus clouds are often harbingers of an approaching change in weather, particularly when they thicken and progressively cover the sky. In such cases, they frequently herald a warm front that may bring precipitation within 12 to 36 hours. Isolated, slowly drifting cirrus clouds against an otherwise clear sky, however, are indicative of stable fair weather. The direction of movement of cirrus clouds provides insight into wind conditions in the upper troposphere and can indicate the position of the jet stream. Cirrus clouds also play a role in the Earth's radiation budget, as they partially trap outgoing longwave thermal radiation and thus contribute to a slight warming effect.
Facts
- WMO-Code
- Ci
- Height layer
- High clouds
- Typical height
- 6.0 - 12.0 km
- Genus
- CIRRUS