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absolute instrument—An instrument the calibration of which can be determined by means of simple physical measurements on the instrument. Compare secondary instrument.
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absolute momentum—(Also called absolute linear momentum.) The (linear) momentum of a particle as measured in an absolute coordinate system; hence, in meteorology, the sum of the (vector) momentum of the particle relative to the earth and the (vector) momentum of the particle due to the earth's rotation.
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absolute monthly maximum temperature—Highest daily maximum temperature observed during a given calendar month over a specified period of years.
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absolute monthly minimum temperature—Lowest daily minimum temperature observed during a given calendar month over a specified period of years.
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Absolute Radiation Scale—[Abbreviated ARS; also referred to as the World Radiation Reference (WRR).] A radiation scale for measurement of solar exitance (irradiance). Prior to 1956, the Ångström Scale (ÅS) (1905) and Smithsonian Scale (SS) (1913) were used. Each scale was calibrated against a different radiation detector (i.e., the Ångström compensation pyrheliometer and water-stirred pyrheliometer, respectively), and yielded slightly different values for the irradiance, with the ÅS reading roughly 3.5% lower than the SS. The International Pyrheliometric Scale (IPS), defined in 1956, represented a numerical compromise between these two scales. In 1975, the IPS was replaced by the Absolute Radiation Scale (ARS). The ARS is calibrated against six absolute cavity radiometers maintained at the World Radiation Center in Davos, Switzerland. The variation among the six radiometers is about 0.3%. The IPS was found to give measured irradiance levels that were about 2%–3% percent lower than the more precise ARS.
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absolute refractive index—(Or absolute index of refraction.) See refractive index.
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