fluctus
flu
Cumulus fluctus
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Description
The name "fluctus" (Latin for wave) describes a rare and short-lived cloud formation that appears in the sky like breaking ocean waves. Fluctus is a supplementary feature and can occur with various cloud genera such as cirrus, altocumulus, stratocumulus, stratus, and cumulus. The characteristic wave-like structures are caused by Kelvin-Helmholtz instabilities at the interface between two air layers with different flow velocities. Since these formations typically last only a few minutes, they are considered a particularly rare sight in the sky.
Identification Features
- Wave-like, breaking structures resembling ocean waves
- Appear in regular, parallel patterns
- Very short-lived, often visible for only 1 to 3 minutes
- Form at the top of a cloud layer
- Crests of the waves "break" in one direction
- Can occur at various altitudes
- Appear under conditions of strong vertical wind shear
Related genera
fluctus is not a distinct cloud type, but a supplementary feature that is given in addition to the genus name. It can occur with the following genera: Ci, Ac, As, Sc, Cu.
Meteorological Significance
Fluctus clouds are direct visual evidence of Kelvin-Helmholtz instabilities in the atmosphere and indicate significant wind shear between different air layers. For aviation, they are an important indicator of possible turbulence (clear air turbulence) at the corresponding altitudes. From a meteorological perspective, they have no direct weather forecasting significance in themselves, but rather document atmospheric flow dynamics. However, their occurrence can indicate unstable flow conditions that may be accompanied by changes in weather.
Facts
- WMO-Code
- flu
- Height layer
- High clouds
- Genus
- CIRRUS