The Kennelly-Heaviside Layer is also known as the E region or just as Heaviside Layer (after Oliver Heaviside). It is a layer of ionised gas occurring at 90-150km in altitude, one of several layers in the Earth's ionosphere. It reflects medium-frequency radio waves, and because of this reflection radio waves can be propagated beyond the horizon.

Propagation is affected by time of day. During the daytime the solar wind presses this layer closer to the Earth, thereby limiting how far it can reflect radio waves. On the night side of the Earth, the solar wind drags the ionosphere further away, thereby greatly increasing the range which radio waves can travel by reflection, called skywave. The extend of the effect is further influenced by the season (because of the differing distance between Earth and the Sun), and the amount of sunspot activity.

History

Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (1861-1949) and the British physicist Oliver Heaviside (1850-1925). However, it was not until 1924 that its existence was detected by Edward V. Appleton.

Cultural impact

The "Heaviside Layer" is used as a symbol for heaven (in the afterlife sense) in Andrew Lloyd Webber's musical Cats. This reference is based on a quote found in a letter written by T. S. Eliot, whose book Old Possum's Book of Practical Cats forms the basis of the musical.