Definition
An older name for the E layer of the ionosphere, a region of electrically charged particles roughly 60 to 90 miles above the Earth's surface that reflects medium and high frequency radio waves back toward the ground, allowing long-distance radio communication beyond line of sight.
Plain English
A layer of the upper atmosphere that acts like a mirror for certain radio waves, bouncing them back to Earth so signals can travel much farther than they otherwise could.
Context Anchor
Seen in discussions of radio wave travel, long-range radio communication, and why some lower-frequency signals may behave differently at night or over long distances.
Derivation
Named after Arthur Kennelly (American engineer) and Oliver Heaviside (British physicist), who independently proposed in 1902 that a conducting layer must exist in the upper atmosphere to explain how radio signals could travel around the curve of the Earth. Knowing the names are people, not technical concepts, removes the mystery from the term.
Why Pilots Care
It determines the usable range of HF radio transmissions for oceanic, polar, and remote-area flights where VHF and satellite coverage may be limited.
Analogy
Think of it like a high, invisible ceiling that does not stop all radio signals, but can bend some of them back toward the ground.
Grounding Statement
Far above the airplane, sunlight and other energy can charge thin air enough that some radio waves are bent back toward Earth.
Intuition Check
Do not picture this as a solid layer or a weather cloud. It is a thin region of charged air that affects some radio waves, not all radio communication.
Example Sentence 1
The textbook noted that the Kennelly-Heaviside Layer is now more commonly called the E layer of the ionosphere.
Example Sentence 2
Solar flares can disturb the Kennelly-Heaviside Layer and cause temporary loss of HF communications.