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Section S S index 831-839 of 1376 terms
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sporadic E-layer—A narrow layer of enhanced electron and ion density in the lower ionosphere. Most sporadic E-layers are thought to be formed by the action of dynamo forces on metallic positive ions deposited by incoming meteors.
spot wind—In air navigation, wind direction and speed, either observed or forecast if so specified, at a designated altitude over a fixed location. Compare track wind, sector wind.
SPOT—Abbreviation for Satellite pour l'Observation de la Terre.
spotting—See map plotting.
spout—See waterspout.
spray electrification—A process of charge separation associated with the mechanical disruption of liquid drops and believed to be based on the electrical double layer at the air–water interface. Spray electrification is the common explanation for the electric field generation in the vicinity of waterfalls.
spread-F—Term derived from ionospheric sounding when the echo from the F-region of the ionosphere becomes blurred, with multiple echoes occurring over a range of distances and frequencies. Spread-F is basically caused by the existence of many small-scale irregularities in electron density within the echoing region, instead of the normal smooth variation of electron density with height.
spread skill correlation—The correlation between the spread of an ensemble forecast and the skill of the ensemble mean. Even in a perfect model, the spread skill correlation may be rather low since the spread is an estimate of the expected value of the difference between the ensemble mean and the verification, not an estimate of this difference in individual cases. See ensemble spread.
spread—1. (Also called variability.) The general departure of individual values from central tendency. Spread is reflected geometrically in the probability curve as the width of the region over which the probability density is appreciable. See scatter, variance. 2. Popular contraction for dewpoint spread.
spring crust—A type of snow crust, formed when loose firn is recemented by a decrease in temperature. It is most common in late winter and spring.
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