E1 layer

E layer

A highly ionized part of the ionosphere with an ionization of around 10⁵ free electrons/cm³. It is found at heights of 60 to 90 miles (100 to 150 km). Its height varies between summers and winters as well as days and nights. It is most pronounced in the daytime but does not entirely disappear at night. It reflects electromagnetic waves from 100 kHz to 20 MHz back to the earth. There is some evidence to indicate a second layer above the normal E layer, the E₂ layer, which is located at about 90 miles (150 km). The E layer plays an important role in the quality of radio communications; radio waves bounce off the E layer. Also called the E1 layer, the Kennelly-Heaviside layer, and the Heaviside layer—the latter after its discoverer. See Heaviside layer.

An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved