| Section E | E index | 441-449 of 498 terms |
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excessive precipitation—Precipitation (generally in the form of rain) of an unusually high rate. The expression is usually used qualitatively, but several meteorological services have adopted quantitative limits. In general, formulas for determining criteria for excessive precipitation take the following form:  where R is the amount of rainfall in t minutes, and a and b are constants. For longer storm periods, the expressions used are often of the type  where T is the time in hours.
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excited state—Configurations of an atom or molecule that contain more energy than the ground state. Excited electronic or vibrational states usually occur following the absorption of radiation of the correct frequency, and are lost by processes such as emission of the radiation (fluorescence) or by reaction. Many electronically excited states are more reactive than the ground state, for example, the first excited state of atomic oxygen, O(1D).
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exhalation—1. In soil science, the process by which radioactive gases escape from the surface layers of soil or loose rock where they are formed by decay of radioactive salts. The exhalation of radioactive gases, notably radon and thoron, increases with soil temperature and so normally exhibits a single daily maximum around midday. Decreases of atmospheric pressure normally increase the exhalation, and freezing of the surface soil layers usually greatly reduces it. 2. The streaming forth of volcanic gases; also the escape of gases from a magnetic field.
Israël, 1951: Compendium of Meteorology, 155–158.
American Geological Institute, 1997: Glossary of Geology, 4th ed., J. A. Jackson, Ed., p. 221.
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exhaust trail—(Or engine exhaust trail.) A condensation trail that forms when the water vapor from fuel combustion of the aircraft engine is mixed with and saturates (or supersaturates) the air in the wake of the aircraft. Exhaust trails are of more common occurrence and of longer duration than aerodynamic trails.
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