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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z | |
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First Edition Preface Second Edition Preface Acknowledgments
Section A A index 21-29 of 917 terms
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abscissa—The horizontal coordinate in a two-dimensional system of rectangular Cartesian coordinates; usually denoted by x; also, the horizontal axis of any graph.
absolute altitude—The true vertical distance above the terrain. Compare true altitude.
absolute angular momentum—The angular momentum as measured in an absolute coordinate system; hence, the vector product of the position vector of a particle into the absolute momentum of the particle. In the atmosphere the absolute angular momentum M per unit mass of air is equal to the sum of the angular momentum relative to the earth and the angular momentum due to the rotation of the earth: where r is the distance from the center of the earth to the particle, u the relative eastward component of velocity, φ the latitude, and Ω the angular rotation rate of the earth. Since the earth's atmosphere is shallow, the variable r is often replaced by the constant a, defined as the radius of the earth. The absolute angular momentum per unit mass is then approximated by See angular-momentum balance, conservation of angular momentum.
absolute annual range of temperature—The difference between the highest and lowest temperature observed at a location.
absolute cavity radiometer—A combined electrical substitution and cavity radiometer where the electrical substitution inequivalence, efficiency of the cavity, the area of the entrance aperture, radiative and conductive losses, and other energy exchanges are accounted for such that the electrically substituted heating can be absolutely equated to the radiant heating of the detector. Most currently existing absolute cavity radiometers are designed for the measurement of direct solar irradiance. The World Radiation Reference (WRR) scale for solar irradiance observations used in many meteorological and climatological applications is defined by a group of well-characterized absolute cavity radiometers maintained by the World Radiation Center (WRC) in Davos, Switzerland.
absolute coordinate system—(Or absolute reference frame.) The inertial coordinate system that has its origin on the axis of the earth and is fixed with respect to the stars. Thus, any mechanical quantities in meteorology defined with respect to this frame take into account the rotation of the earth. See Coriolis force, absolute vorticity.
absolute drought—In British climatology, a drought period of at least 15 days during which no measurable daily precipitation has fallen. In the United States similar criteria have been used to define a dry spell (which, in turn, has a different definition in Great Britain). Ordinarily, these criteria are applied regardless of the season of the year.
absolute extremes—Highest or lowest temperature observed over the whole period of observation.
absolute humidity—Same as vapor density.
absolute instability—1. The state of a column of air in the atmosphere when it has a superadiabatic lapse rate of temperature (i.e., greater than the dry-adiabatic lapse rate). An air parcel displaced vertically would be accelerated in the direction of the displacement. The kinetic energy of the parcel would consequently increase with increasing distance from its level of origin. See parcel method, conditional instability, absolute stability. 2. (Also called mechanical instability.) The state of a column of air in the atmosphere when its lapse rate of temperature is greater than the autoconvective lapse rate. In such a column the air density would increase with elevation. See also autoconvection.
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