| Section S | S index | 991-999 of 1376 terms |
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steppe climate—(Also called semiarid climate.) The type of climate in which precipitation is very slight but sufficient for the growth of short, sparse grass. This is typical of the steppe regions of south-central Eurasia. In his 1936 climatic classification, W. Köppen assigns maximum values of annual precipitation to separate this dry climate from the rainy climates as follows. For precipitation chiefly in the winter,  For precipitation evenly distributed during the year,  For precipitation chiefly in the summer,  In the above, p is the mean annual precipitation in inches, and t the mean annual temperature in degrees Fahrenheit. (For minimum values of precipitation, see formulas under desert climate.) This scheme was modified by Bailey to  where R is the precipitation falling during the six colder months. In Köppen's system the steppe climate is designated letter code BS. The semiarid climate of Thornthwaite (1931) corresponds closely to the steppe climate.
Köppen, W. P., and R. Geiger, 1930–1939: Handbuch der Klimatologie, Berlin: Gebruder Borntraeger, 6 vols
Thornthwaite, C. W., 1931: The climates of North America according to a new classification. Geogr. Rev., 21, 633–655.
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steppe—An area of grass-covered and generally treeless plains, with a semiarid climate, which forms a broad belt over southeastern Europe and the southwestern part of the former Soviet Union.
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stepped leader—The initial leader of a lightning discharge; an intermittently advancing column of high ionization and charge that establishes the channel for a first return stroke. The peculiar characteristic of this type of leader is its stepwise growth at intervals of about 50– 100 μs. The velocity of growth during the brief intervals of advance, each only about 1 μs in duration, is quite high (about 5 × 107 m s−1), but the long stationary phases reduce its effective speed to only about 5 × 105 m s−1. To help explain its mode of advance, the concept of a pilot streamer was originally suggested, but has been supplanted by analogy to recent work on long laboratory sparks.
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steradian—The SI unit of solid angle that, having its vertex in the center of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere. There are 4π steradians in a sphere.
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stereographic image—(Or stereo image.) A depiction of a three-dimensional object that results from stereoscopic viewing. A stereo image is obtained by simultaneously viewing a cloud, for example, from satellites at different locations from which the height of the cloud may be determined.
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stereographic projection—A type of conformal map in which features on a sphere are projected onto a plane tangent to the sphere. The source of projecting rays is a point diametrically opposite the tangent point. See conformal map.
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stereoscopic image—Two pictures taken with a spatial or time separation that are then arranged to be viewed simultaneously. When so viewed they provide the sense of a three-dimensional scene using the innate capability of the human visual system to detect three dimensions.
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