Kennelly–Heaviside layer
（重定向自E region）
The Kennelly–Heaviside layer, named after Arthur E. Kennelly and Oliver Heaviside, also known as the E region or simply the Heaviside layer, is a layer of ionised gas occurring between roughly 90–150 km (56–93 mi) above the ground — 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.