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D region

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noun
  1. the lowest region of the ionosphere, in which the D layer develops.
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Origin of D region

First recorded in 1925–30
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

British Dictionary definitions for d region

D region

D layer

noun
  1. the lowest region of the ionosphere, extending from a height of about 60 kilometres to about 90 kilometres: contains a low concentration of free electrons and reflects low-frequency radio wavesSee also ionosphere
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Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

d region in Science

D region

  1. The region of the atmosphere that lies in the upper mesosphere, extending from about 70 to 90 km (43 to 56 mi) above the Earth. The D region is responsible for the daytime absorption of high-frequency radio signals; at night, oxygen ions recombine with free electrons and form oxygen molecules that are transparent to such signals, which bounce off of the E region and back to Earth. Also called D layer Compare E region F region.
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The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.