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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 61-69 of 917 terms
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absorptivity—The fraction of incident radiation that is absorbed by matter. Absorptivity may be a function of wavelength and/or direction, and is related to the emissivity of the region by Kirchhoff's law. The absorptivity is identically equal to unity for blackbodies and is independent of wavelength for gray bodies.
abstraction—1. The part of precipitation that does not become direct runoff. 2. The draining of water from a stream into another stream having a more rapid corroding action.
ACC—Abbreviation for Antarctic Circumpolar Current.
accelerated erosion—Erosion increased by human agency to beyond the normal geologic rate.
acceleration of gravity—See gravity.
acceleration—The rate of change with time of the velocity vector of a particle. If u is the vector velocity, the acceleration may be written as Du/Dt, where D/Dt is the material (or total) derivative. For most purposes in hydrodynamics where Eulerian coordinates are employed, the acceleration is decomposed as follows: where ∂u/∂t is called the local acceleration, and u · ∇u is called the convective acceleration.
accelerometer—An instrument that measures acceleration.
acceptance capacity—Quantity of pollutants that a water body can accept without the pollution exceeding a specified level.
acceptance region—A range of values of a sample statistic used to test a hypothesis. In the testing procedure, the sampling region is divided into an acceptance region and a rejection region. If the sample statistic lies within the acceptance region, the null hypothesis (a hypothesis usually based on conventional theory) is provisionally accepted. If the sample statistic lies in the rejection region, the alternative hypothesis that contradicts the null hypothesis is accepted. See significance test.
accessory cloud—A cloud form that is dependent, for its formation and continuation, upon the existence of one of the major cloud genera. It is often an appendage of the parent cloud (as mamma, incus, tuba, arcus), but it also may be an immediately adjacent cloudy mass (as pannus, pileus, velum). See cloud classification.
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