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noctilucent cloud |
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noctilucent cloud [¦näk·tə¦lü·sənt ′klau̇d] (meteorology) A cloud of unknown composition which occurs at great heights and high altitudes; photometric measurements have located such clouds between 45 and 54 miles (75 and 90 kilometers); they resemble thin cirrus, but usually with a bluish or silverish color, although sometimes orange to red, standing out against a dark night sky. How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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| Cloud experts have sighted beautiful noctilucent clouds, or silvery blue ice clouds, over Colorado--1,000 kilometers farther south than usual. These so-called noctilucent ice clouds may become visible as far south as Philadelphia in the next century because of greenhouse gases accumulating in Earth's atmosphere, according to calculations by Gary Thomas of the University of Colorado at Boulder and his colleagues. This connection is important because a significant variability in the yearly number of noctilucent ("glow in the dark") clouds, which are a manifestation of PMCs, has been suggested as an indicator of global climate change. |
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