Cirrus undulatus
Ci un
Cirrus undulatus
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Description
The name "undulatus" (Latin: wavy) describes the characteristic wave structure of this cirrus variety. Cirrus undulatus appears as thin, high ice cloud bands or layers displaying a clearly recognizable wave pattern. This wave structure is created by wind shear in the upper troposphere, where differing wind speeds or directions in adjacent air layers shape the cloud structure into parallel, wave-like bands. The clouds consist exclusively of ice crystals and generally appear white to silvery, with the wave pattern appearing particularly striking at low sun angles. Cirrus undulatus is a rather rarely observed variety that indicates pronounced dynamic processes at great altitude.
Identification Features
- Thin, fibrous or sheet-like cirrus clouds with a clearly recognizable wave pattern
- Parallel bands or stripes at regular intervals
- Very high altitude, typically above 6,000 meters
- White to silvery-transparent appearance
- Wave crests and troughs clearly distinguishable by differences in brightness
- Consists exclusively of ice crystals, therefore often with a silky sheen
- Can extend across large portions of the sky
- Distinguished from Cirrocumulus undulatus by the absence of individual cloudlets and its fibrous base structure
Occurrence by genus
Highlighted: all genera with which undulatus occurs.
Meteorological Significance
Cirrus undulatus indicates pronounced wind shear and wave activity in the upper troposphere, suggesting dynamic processes at altitude. Its appearance can be a sign of an approaching warm front or an advancing frontal system, particularly when cloud cover increases and thickens. For aviation, this cloud form is relevant because the underlying wind shear may point to possible turbulence at cruising altitude. As a weather indicator on its own, however, Cirrus undulatus is not very informative and must be assessed in the context of the overall development of cloud cover. When occurring in isolation without further thickening, weather conditions often remain stable for some time.
Facts
- WMO-Code
- Ci un
- Height layer
- High clouds
- Typical height
- 6.0 - 12.0 km
- Genus
- CIRRUS