Editing Ionosphere (section)

===E layer===
{{main|Kennelly–Heaviside layer}}

The [[Kennelly–Heaviside layer|E layer]] is the middle layer, {{convert|90|to|150|km|mi|sigfig=2|abbr=on}} above the surface of the Earth. Ionization is due to soft X-ray (1–10&nbsp;nm) and far ultraviolet (UV) solar radiation ionization of molecular [[oxygen]] (O{{sub|2}}). Normally, at oblique incidence, this layer can only reflect radio waves having frequencies lower than about 10&nbsp;MHz and may contribute a bit to absorption on frequencies above. However, during intense [[sporadic E]] events, the E{{sub|s}} layer can reflect frequencies up to 50&nbsp;MHz and higher. The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. At night the E layer weakens because the primary source of ionization is no longer present. After sunset an increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer.

This region is also known as the [[Kennelly–Heaviside layer]] or simply the Heaviside layer. Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer [[Arthur Edwin Kennelly]] (1861–1939) and the British physicist [[Oliver Heaviside]] (1850–1925). In 1924 its existence was detected by [[Edward V. Appleton]] and [[Miles Aylmer Fulton Barnett|Miles Barnett]].