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Section S S index 901-909 of 1376 terms
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standard pressure—1. A pressure of one atmosphere, in SI units, 101 325 N m−2. In older works standard pressure sometimes means the arbitrary reference pressure in the expression for potential temperature; but this use of standard pressure should be avoided, given the widespread use of standard pressure in many fields of science to mean a pressure of one atmosphere. Compare standard temperature. In meteorology, the arbitrarily selected atmospheric pressure of 1000 mb to which adiabatic processes are referred for definitions of potential temperature, equivalent potential temperature, etc. Other pressures may be used as standard for specific purposes.
standard project flood—The discharge expected to result from the most severe combination of meteorological and hydrological conditions that are reasonably characteristic of the geographic region involved.
standard propagation—The propagation of radio energy over a smooth spherical earth of uniform dielectric constant and conductivity under conditions of standard refraction in the atmosphere, that is, an atmosphere in which the refractive index decreases uniformly with height at a rate of approximately 40 N-units per kilometer. Standard propagation leads to ray curvature due to refraction with a value approximately one- fourth that of the earth's curvature, giving a radio horizon that is about 15% farther than the distance to the geometric horizon. This is equivalent to straight-line propagation over a fictitious earth with radius of four-thirds the radius of the actual earth. See effective earth radius, superstandard propagation, substandard propagation, standard atmosphere.
standard refraction—See standard propagation.
standard seawater—Same as normal water.
standard target—A radar target of known radar cross section used to calibrate a radar or monitor its performance. Metal spheres or corner reflectors of known dimensions are examples.
standard temperature and pressure—(Abbreviated STP; also called normal temperature and pressure.) A phrase used in physics to indicate a temperature of 0°C and a pressure of one standard atmosphere.
standard temperature—In physics, usually the ice point (0°C); less frequently, the temperature of maximum water density (4°C). In meteorology, this has no generally accepted meaning, except that it may refer to the temperature at zero pressure altitude in the standard atmosphere (15°C).
standard time of observation—A time specified in the manual on the Global Observing System for making meteorological observations.
standard visibility—Same as meteorological range.
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