Also found in: Dictionary, Thesaurus.
The lower layer of the ionosphere, it has the best concentrations of ions—about 106/cm3. Its height is around 100 miles (160 km). Its height varies in summers and winters as well as during the days and nights. It affects daytime radio wave propagation and reflects waves from 1.5 to above 30 MHz. See F layer.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved