Tradition has made the long, flat cloud-streak near the horizon the type form of stratus cloud. But if that same cloud-streak were overhead it would appear merely as a low cloud covering more or less of the sky. When a fog lifts, it forms a stratus cloud; and if it floats away toward the observer’s horizon it becomes a long gray cloud streak. In the first case one is looking at the under side of the surface; in the second, at the edge. The components of a stratus cloud may be fog, smoke or dust—or even all three.
Qualifying Descriptive Terms.—Usage in the matter of descriptive terms is not uniform. The following have been suggested.[1]
Fibrous, characteristic of streaks of falling rain or snow seen from a distance.
Smooth, characteristic of sheet-like clouds.
Flocculent, scaly, flaky, in small tufts (floccus, a tuft of wool).
Waved, or in rolls, characteristic of waves and windrows observable In billow clouds.
Round-topped, characteristic of the summits of clouds produced by rising currents.
Down-bulged, or round-holed, characteristic of the lower sides of clouds produced by down-draughts.
Ragged, characteristic of forming and of evaporating clouds in turbulent wind.
Recording Cloud Conditions.—The International Cloud Committee recommends the following instructions for the guidance of observers:
Kind or character.—Clouds may be designated by name, or by symbol, as Ci-St, for cirro-stratus. Where doubt exists, the number of the picture in the classification scheme should be designated.
Direction.—If the clouds are high the motion may be observed best by noting their position relative to a fixed object—a tree, or a flag-pole. Where the movement of the cloud is very slow, a rest for the head and shoulders may be necessary. The direction is best observed when clouds are near the zenith. The movement and direction of horizon clouds are apt to be decep- tive, giving to the observer an imperfect perspective. When possible, a nephoscope should be used if the direction is doubtful.
- ↑ C. F. Brooks, Monthly Weather Review, Sept., 1920. Seven terms noted above are used for form; five—transparent, semi-transparent, medium, dense, and very dense—describe density; three—coarse, medium, and fine—indicate the degree of fineness. These terms, while they do not alter the International Cloud Committee’s classification, add very materially to its clearness.
