| 单词 | d region |
| 释义 | D regionnounthe lowest region of the ionosphere, in which the D layer develops. Origin of D regionFirst recorded in 1925–30 Words nearby D regiondredging machine, Dred Scott decision, dree, dreg, dreggy, D region, dregs, Dreibund, dreich, dreidel, dreigh Dictionary.com UnabridgedBased on the Random House Unabridged Dictionary, © Random House, Inc. 2020 British Dictionary definitions for D regionD region D layernounthe 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 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 Scientific definitions for D regionD region 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. The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved. |
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