īˈänə+ˌ- noun
Etymology: ion + -o- + -sphere
: the part of the earth's atmosphere beginning at an altitude of about 25 miles and extending outward 250 miles or more, containing free electrically charged particles by means of which radio waves are transmitted to great distances around the earth, and consisting of several regions within which occur one or more layers that vary in height and ionization with time of day, season, and the solar cycle, the gases in this part of the earth's atmosphere being ionized by ultraviolet rays from the sun and to a lesser extent by charged particles from the sun — see d region , e region , f region
• ion·o·spher·ic ī|änə|sfirik, -fer- adjective