| Section A | A index | 591-599 of 917 terms |
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anthelic arcs—A group of halos, each of which passes through the anthelion. Four mechanisms have been proposed for producing arcs of various shapes that nevertheless pass through the anthelion. Each of the four predicted shapes has been documented photographically. Each mechanism involves refraction and internal reflection in columnar ice crystals, but they differ in the particular crystal faces involved.
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anthelion—A luminous white spot that appears on the parhelic circle 180° in azimuth away from the sun. The origin of anthelion is not settled. The brightness of this spot may be due partly to the superposition of the parhelic circle and of the anthelic arcs, which intersect the parhelic circle at this point. Other candidate mechanisms giving light to anthelion have been suggested.
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anthropogenic climate change—Climate change that occurs as a result of human activities.
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anthropogenic emissions—Emissions to the atmosphere of gases as a result of human activity. The term is often used to describe, but is not restricted to, the exhaust from combustion events.
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anthropogenic heat—Heat released to the atmosphere as a result of human activities, often involving combustion of fuels. Sources include industrial plants, space heating and cooling, human metabolism, and vehicle exhausts. In cities this source typically contributes 15–50 W m−2 to the local heat balance, and several hundred W m−2 in the center of large cities in cold climates and industrial areas. Compare urban heat island.
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anthropogenic—Human-induced or resulting from human activities; often used to refer to environmental changes, global or local in scale.
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