9th September 2005
Cirrocumulus
Source: Excerpt from The Book " Weather "
Distribution: Worldwide. Height: Above 16,500 feet. Cause: Saturation of a large airmass at high levels, combined with instability at cloud level. Associated Weather: Increasing cover may indicate an approaching frontal system. Cirrocumulus, like cirrostratus, occurs when a large area of moist air at a high level of the atmosphere reaches saturation and forms ice crystals. What differentiates cirrocumulus from cirrostratus is the presence of instability at cloud level. This gives the cloud its cumuliform appearance.
In isolation, this formation does not normally have any great significance. However, if there is a steady increase in this cloud over a period of time, it may indicate the approach of a frontal system.
Cirrocumulus is one of the most attractive of all clouds, often forming spectacular patterns that may stretch for hundreds of miles across the sky. One dramatic form of cirrocumulus is cirrocumulus undulatus, which appears as a fine, rippled pattern in the sky.
As with other undulatus forms, these ripples are produced by atmospheric waves generated by wind shear. However, in the case of cirrocumulus undulatus, the entire structure has a much finer appearance. This is partly due to the fact that atmospheric waves formed at high altitudes tend to have a shorter wavelength than those formed in the middle layers, but it is also a result of the greater distance between the cloud formation and the observer on the ground.
Acknowledgement due: John W. Zillman, William J. Burroughs,
Bob Crowder, Ted Robertson, Eleanor Vallier-Talbot and Richard Whitaker.
Check out Skyscapes for cloud photos taken from the aircraft.
