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American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
(General Physics) the highest region of the ionosphere, extending from a height of about 150 kilometres to about 1000 kilometres. It contains the highest proportion of free electrons and is the most useful region for long-range radio transmission. Also called: Appleton layer See also ionosphere
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014
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|Noun||1.||F region - the highest region of the ionosphere (from 90 to 600 miles up) which contains the highest concentration of free electrons and is most useful for long-range radio transmission|
ionosphere - the outer region of the Earth's atmosphere; contains a high concentration of free electrons
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