Ionosphere

[ahy-on-uh-sfeer] /aɪˈɒn əˌsfɪər/

noun
1.
the region of the earth’s atmosphere between the stratosphere and the exosphere, consisting of several ionized layers and extending from about 50 to 250 miles (80 to 400 km) above the surface of the earth.
/aɪˈɒnəˌsfɪə/
noun
1.
a region of the earth’s atmosphere, extending from about 60 kilometres to 1000 km above the earth’s surface, in which there is a high concentration of free electrons formed as a result of ionizing radiation entering the atmosphere from space See also D region, E region, F region
n.

1926, from ion + sphere. Coined by Scottish radar pioneer Robert A. Watson-Watt (1892-1973). So called because it contains many ions.
ionosphere
(ī-ŏn’ə-sfîr’)
A region of the Earth’s upper atmosphere, extending from a height of 70 km (43 mi) to 400 km (248 mi) and containing atoms that have been ionized by radiation from the Sun. The ionosphere lies mostly in the lower thermosphere and is subdivided into three regions, the D region (70 km to 90 km; 43 to 56 mi), the E region (90 km to 150 km; 56 to 93 mi), and the F region (150 km to 400 km; 93 to 248 mi). The concentration of ionized atoms is lowest in the D region, intermediate in the E region, and highest in the F region. The ionosphere is useful for radio transmission because radio waves, which normally propagate in straight lines, are reflected off the ionized gas particles, thereby being transmitted long distances across the Earth’s curved surface. See more at D region, E region, F region.

ionosphere [(eye-on-uh-sfeer)]

A region of the atmosphere that begins at an altitude of about thirty miles.

Note: In this region, free particles carrying an electrical charge, atoms ionized (see ionization) by radiation from the sun, reflect radio waves. “Bouncing” radio waves off the ionosphere makes communication possible over long distances of the surface of the Earth.