D region

Save This Word!

the lowest region of the ionosphere, in which the D layer develops.
Were you ready for a quiz on this topic? Well, here it is! See how well you can differentiate between the uses of "was" vs. "were" in this quiz.
Question 1 of 7
“Was” is used for the indicative past tense of “to be,” and “were” is only used for the subjunctive past tense.

Origin of D region

First recorded in 1925–30
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

How to use D region in a sentence

British Dictionary definitions for D region

D region

D layer

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
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 region

D 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.