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Cloud Art: Cloud Classification
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Howard based his organizational model of clouds on the system of classification introduced by Swedish botanist Carl von Linne. The Linnean system employs a binomial nomenclature designated by a pair of Latin names; one that defines the cloud genus and the second that indicates cloud species. The names Howard chose for his three major types of clouds conveyed a sense of the outward characteristics:
Cirrus
(from Latin for "fiber" or "hair")
In Howard's words: "parallel, flexuous, or diverging fibres, extensive in any or in all directions"
Cumulus
(from the Latin for "heap" or "pile")
"convex or conical heaps, increasing upwards from a horizontal base"
Stratus
(adapted from the Latin stratum for "layer" or "sheet")
"a widely extended continuous horizontal sheet, increasing from below upwards"
(Cumulo-, Cirro-, or Stratus-) Nimbus
(from the Latin for "cloud")
...which Howard considered to be a rainy combination of the three major types— "The rain cloud. A cloud or system of clouds from which rain is falling..."
His intermediate types also included:
Cirro-Cumulus
"Small, well defined roundish masses, in close horizontal arrangement or contact"
Cirro-Stratus
"Horizontal or slightly inclined masses attenuated towards a part or the whole of their circumference, bent downward, or undulated, separate or in groups consisting of small clouds having these characteristics"
Cumulo-Stratus
"The cirro-stratus blended with the cumulus, and either appearing intermixed with the heaps of the latter or super-adding a wide spread structure to its base "
There were a number of attempts to modify this simple classification over the years, but the naming of clouds given to us by Howard has remained largely intact. The first true change to Howard's list was "stratocumulus", replacing the cumulo-stratus. The ultimate acceptance of stratocumulus as "a layer of cloud not flat enough to be called pure stratus by rising into lumps too irregular and not sufficiently rocky to be called true cumulus" occurred in the late 19th century.1
The present-day classification adopted by the World Meteorological Organization is as follows:
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High Clouds (bases above 6 km)
- Cirrus (Howard, 1803)
- Cirrocumulus (Howard, 1803)
- Cirrostratus (Howard, 1803)
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Middle Clouds (bases between 2 and 6 km)
- Altocumulus (Renou, 1870)
- Altostratus (Renou, 1870)
- Nimbostratus (International Commission for the Study of Clouds, 1930)
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Low Clouds (bases below 2 km)
- Stratocumulus (Kaemtz, 1841)
- Stratus (Howard, 1803)
- Cumulus (Howard, 1803)
and the final cloud type extending through all ranges of altitudes is
- Cumulonimbus (Weilbach, 1880)
1 Stephens, G. L., 2003: The Useful Pursuit of Clouds, American Scientist, vol. 91, pp. 442-449.
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