| Section A | A index | 661-669 of 917 terms |
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aquifer test—A test to determine hydrologic properties of the aquifer involving the withdrawal of measured quantities of water from, or addition of water to, a well and the measurement of resulting changes in head in the aquifer both during and after the period of discharge or additions.
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aquifer—A layer of saturated geologic materials that could yield water to springs or wells.
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aquifuge—A geologic formation that has no interconnected openings and hence cannot receive or transmit water.
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aquitard—A geologic formation that is not permeable enough to yield significant quantities of water to wells, but on a regional scale can contribute significant water to the underlying or overlaying aquifers.
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aracaty—Northeast wind of Ceará, Brazil.
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Arago distance—The angular distance from the antisolar point to the Arago point. The Arago distance is sensitive to the presence of foreign scattering particles in the atmosphere since these increase the contribution of the negative (horizontal) component of skylight polarization and hence shift the location of the point where the negative component is just equalled by the positive component. Thus the Arago distance is a useful measure of atmospheric turbidity. Its value is generally close to 20°, and is a function of solar elevation angle and of the wavelength of the light with which polarization is studied.
Sekera, Z., 1951: Compendium of Meteorology, 79–90.
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Arago point—One of the three commonly detectable points along the vertical circle through the sun at which the degree of polarization of skylight goes to zero; a neutral point. The Arago point, so named for its discoverer, is customarily located at about 20° above the antisolar point, but it lies at higher elevations in turbid air. The latter property makes the Arago distance a useful measure of atmospheric turbidity. Measurements of the location of this neutral point are typically more easily carried out than measurements of the Babinet point and the Brewster point, both of which lie so close to the sun (about 20° above and below the sun, respectively) that glare problems become serious.
Neuberger, H., 1951: Introduction to Physical Meteorology, 196–204.
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