A component of the Earth’s ionosphere, at an altitude of 110 km; also known as the Heaviside layer after the English physicist Oliver Heaviside (1850–1925). It is used as a reflective surface by radio operators. Electron densities in the E layer show diurnal variation, being greater during daytime. Absorption of radio waves by the denser daytime E layer can be a problem. Localized patches of sporadic E ionization which commonly appear at the same atmospheric level during the summer months can also disrupt short-wave radio communication.