| Section S | S index | 1251-1259 of 1376 terms |
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superior air—An exceptionally dry mass of air formed by subsidence and usually found aloft but occasionally reaching the earth's surface during extreme subsidence processes. It is often found above tropical maritime air, bounded by the trade-wind inversion.
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superior mirage—A mirage in which the image or images are displaced upward from the position of the object. If only a single image of distant objects is seen, then the term looming is often applied: A horizontal surface appears to curve upward with increasing distance and terminate in a relatively distant optical horizon. The looming might be accompanied by either stooping or towering. The superior mirage is most striking when it exhibits three or more images. The upper and lower images are always erect, while a single middle image will be inverted. No matter the number, images will alternate between erect and inverted, although sometimes a pair will appear back to back and might be interpreted as a single image. Although textbooks sometimes suggest that what is seen is an object and an even number of images, all are images, and have positions and magnifications that differ from that of the object. What is seen is dependent upon both the distance to objects and the height of the eye. A change of either can produce markedly different image characteristics. Superior mirages occur over a surface when (molecular number) density decreases with height, but are always most striking when temperature increases with height. Then, what is seen (for a particular distance and observing height) depends critically on the shape of the temperature (and thus, the refractive index) profile. Everything from stooping to towering to multiple images is a possible result of fairly simple profiles. A common profile, a lifted temperature inversion, can not only produce the three-image mirage but, since internal gravity waves often occur on such an inversion, the resulting periodic horizontal inhomogeneity can also produce a higher number of images. Such lifted inversions are common over, but hardly confined to, enclosed bodies of water on warm afternoons when the warmer air from the surrounding land flows over the colder water. Compare inferior mirage, sinking.
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supernumerary rainbows—(Or supernumerary bows.) A series of fine weakly colored bows that can frequently be seen just inside the primary rainbow. When formed in rain showers, where there is a broad distribution of drop sizes, these bows are mainly seen near the top of the rainbow arch, but fade toward the vertical portions of the primary bow. They owe their name (beyond the prescribed number) to the fact that an explanation of rainbows based upon a treatment of light as a series of rays is incapable of accounting for them. However, when light is treated as a wave, the supernumerary bows become higher-order interference maxima, for which the primary bow is but the first maximum. In this sense, the supernumerary bows are as much a part of the primary bow as are, say, its colors.
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superposed-epoch method—A technique used to study the relationship between two time series, where one series records the occurrence or nonoccurrence of a discrete event of particular interest and the other consists of data for a hypothetically related variable. Relationships are established or rejected by comparison of variable behavior before or after the occurrence of like events. As a meteorological example, the method might be used to examine the influence of sunspot maxima (discrete events) on cloud cover (the variable).
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supersaturation—1. In meteorology, the condition existing in a given portion of the atmosphere (or other space) when the relative humidity is greater than 100%, that is, when it contains more water vapor than is needed to produce saturation with respect to a plane surface of pure water or pure ice. Such supersaturation does develop because frequently there is no “plane surface of pure water (or ice)” available. In the absence of water surfaces and in the absence of condensation nuclei or any wettable surfaces, phase change from vapor to liquid cannot occur due to the free energy barrier imposed by the surface free energy of the embryonic droplets that would then have to form by spontaneous nucleation. Humid air, purified of all foreign nuclei, can be expanded in cloud chambers to relative humidities of the order of 400% without any condensation taking place. Cloud condensation occurs in our atmosphere at relative humidities near 100% only because nature provides an abundance of condensation nuclei. 2. In physical chemistry, the condition existing in a solution when it contains more solute than is needed to cause saturation. Thermodynamically, this type of supersaturation is closely allied to supersaturation of a vapor since the solute cannot crystallize out in solutions free from impurities or seed crystals of the solute.
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supersonic—Referring usually to an object moving faster than the speed of sound in the gas or liquid surrounding it.
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superstandard propagation—The propagation of radio waves under conditions of superstandard refraction (superrefraction) in the atmosphere; that is, refraction by an atmosphere or section of the atmosphere in which the refractive index decreases with height at a rate of greater than 40 N-units per kilometer. Superstandard propagation produces greater than normal downward bending of radio waves as they travel through the atmosphere, giving extended radio horizons and increased radar coverage. It is caused primarily by propagation through layers near the earth's surface in which the dewpoint temperature is rapidly decreasing or the temperature is increasing with height. Such conditions are commonly observed near coastlines when a layer of warm dry air overlies a cool moist layer adjacent to the ocean surface. A layer in which the downward bending is greater than the curvature of the earth is a radio duct. Frequently, the general term, anomalous propagation, is used for superstandard propagation. See standard propagation, substandard propagation.
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supertyphoon—A typhoon with maximum sustained 1-min mean surface winds of 67 m s−1(130 knots) or greater.
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