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Section C C index 251-259 of 1157 terms
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chemical tracers—See tracer.
chemiluminescence—See luminescence.
chemisorption—Adsorption of a chemical onto a surface in which the strength of the interaction is somewhat stronger than pure physical adsorption, and more like a chemical bond. A bond strength of around 80 kJ mol−1 is often taken to be indicative of a true chemical interaction. In some cases, it is thought that chemical modification of the adsorbed species occurs.
chemosphere—The vaguely defined region of the upper atmosphere in which photochemical reactions take place. It is generally considered to include the stratosphere (or the top thereof) and the mesosphere, and sometimes the lower part of the thermosphere. This entire region is the seat of a number of important photochemical reactions involving atomic oxygen O, molecular oxygen O2, ozone O3, hydroxyl OH, nitrogen N2, sodium Na, and other constituents to a lesser degree. See atmospheric shell.
chergui—An east or southeast desert wind in Morocco (North Africa), especially in the north. It is persistent, very dry and dusty, hot in summer, cold in winter. It blows with high pressure in the Mediterranean and isobars run nearly parallel with the coast. It is said to be most frequent in the 40 days following 11 or 12 July, a period known as the Smaïm. Compare simoom.
Chezy equation—An empirical equation relating the mean velocity of flow to channel characteristics. It is expressed as where C is the Chezy resistance coefficient, Sf the gradient of the total head line, and R the hydraulic radius. For discharge Q, where A is the cross-sectional area. See Manning equation.
chi-square test—A statistical significance test based on frequency of occurrence; it is applicable both to qualitative attributes and quantitative variables. Among its many uses, the most common are tests of hypothesized probabilities or probability distributions (goodness of fit), statistical dependence or independence (association), and common population (homogeneity). The formula for chi square (χ2) depends upon intended use, but is often expressible as a sum of terms of the type (f − h)2/h where f is an observed frequency and h its hypothetical value.
chibli—Same as ghibli.
chichili—See chili.
Chile Current—See Peru/Chile Current.
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