| Section S | S index | 511-519 of 1376 terms |
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small-craft warning—A warning, for marine interests, of impending winds up to 28 knots (32 mph). After 1 January 1958, the storm-warning signals for this condition became 1) one triangular red pennant by day and 2) a red lantern over a white lantern by night. See storm warning.
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small hail—Hail with a diameter less than 0.64 cm (0.25 in.). See ice pellets.
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small-ion combination—Either of two processes by which small ions disappear. The first of these processes is the union of a small ion and a neutral Aitken nucleus to form a new large ion; the second is the neutralization of a large ion by the small ion. The rate at which these processes occur is expressed by the magnitude of the combination coefficient for each process.
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small ion—(Also called light ion, fast ion.) An atmospheric ion of the type that has the greatest mobility and hence, collectively, is the principal agent of atmospheric conduction. The exact physical nature of the small ion has never been fully clarified, but much evidence indicates that each is a singly charged atmospheric molecule (or, rarely, an atom) about which a few other neutral molecules are held by the electrical attraction of the central ionized molecule. Estimates of the number of satellite molecules are as high as twelve. When freshly formed by any of several atmospheric ionization processes, small ions are probably singly charged molecules, but after a number of collisions with neutral molecules they acquire (actually, in a fraction of a second) their cluster of satellites. Even with these satellites clustering about the central charged molecules, the ion mobility of the resulting complex is of the order of 104 times greater than that of large ions. Negative small ions exhibit slightly greater mobilities than positive small ions, 1.9×10−4 m s−1 per volt cm−1 being typical of negative, and 1.4×10−4 m s−1 per volt m−1 being typical of positive small ions in dry air at sea level. Small ions may disappear either by direct recombination with oppositely charged small ions or by combination with neutral Aitken nuclei to form new large ions, or by combination with large ions of opposite sign. The concentration of small ions near sea level is typically about 5×10−4 of each sign per m3, both over the oceans and over land. This concentration increases with altitude, and at 18 km it is about 10−3 per m3.
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smaze—(Rare.) A combination of smoke and haze; or, a very light smoke condition that resembles haze.
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