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Section S S index 201-209 of 1376 terms
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secondary ice crystal—An ice crystal formed by a process other than homogeneous or heterogeneous nucleation, as by shatter of a drop freezing on accretion, or breakup of an ice particle on evaporation. See ice multiplication.
secondary instrument—An instrument with calibration determined by comparison with an absolute instrument.
secondary low—Same as secondary cyclone.
secondary pollutants—Pollutants that are formed in the atmosphere as a result of chemical reactions. Secondary pollutants are often photochemical oxidants such as ozone or nitrogen dioxide, or components of acid rain such as sulfuric acid or nitric acid.
secondary rainbow—Distinguished from other rainbows by its angular radius, color order, and brightness. The bow is seen between about 50° and 54° from the antisolar point (shadow of the observer's head) or, equivalently, between 130° and 134° from a light source (such as the sun). Reds are found to the inside of the bow (closest to the primary bow) with the blues to the outside. The secondary bow is usually dimmer than the primary bow. Any theory of the bow that approximates the behavior of light as a ray attributes the secondary bow to light that has undergone two internal reflections. The losses accompanying the additional reflection account for the bow being fainter than the primary bow. This may mean that the bow has insufficient contrast to be distinguished from the background. It is sometimes incorrectly asserted that the extra reflection, by itself, is responsible for the reversal of colors from those of the primary bow. See also rainbow, supernumerary rainbows; compare primary rainbow.
secondary scattering—See multiple scattering.
sector scan—A radar scanning procedure in which the antenna sweeps through an interval of azimuth less than the full 360° at a fixed elevation angle. Often the azimuth extent of a sector scan may be only a few degrees in order to concentrate the observations on a particular storm or region of a storm.
sector wind—The average observed or computed wind (direction and speed) at flight level for a given sector of an air route. Sectors for over-ocean flights usually consist of 10 degrees of longitude. Compare track wind, spot wind.
sectorized image—Satellite imagery that is reformatted into subsections covering specified geographic areas.
secular trend—Same as secular variation.
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