ionosphere

noun

ion·​o·​sphere ī-ˈä-nə-ˌsfir 

: the part of the earth's atmosphere in which ionization of atmospheric gases affects the propagation of radio waves, which extends from about 30 miles (50 kilometers) to the exosphere, and which is contiguous with the upper portion of the mesosphere and the thermosphere

also : a comparable region of charged particles surrounding another celestial body (such as Venus)

ionospheric

ˌī-ˌä-nə-ˈsfir-ik 

-ˈsfer-

adjective

ionospherically

ˌī-ˌä-nə-ˈsfir-i-k(ə-)lē 

-ˈsfer-

adverb

Examples of ionosphere in a Sentence

Recent Examples on the Web

For the last 11 years, the spacecraft has explored how Mars' upper atmosphere and ionosphere interact with the Sun and the solar wind to examine the loss of the Martian atmosphere into space, according to NASA. —Charna Flam, PEOPLE, 12 Dec. 2025

One bolt reached an extraordinary -303 kilo-ampères (the minus sign indicates the lightning's polarity, not that the current was less than zero), producing an intense electromagnetic pulse (EMP) that lit up the ionosphere. —Daisy Dobrijevic, Space.com, 25 Nov. 2025

Their mission goal is to monitor magnetic signals from Earth’s core and mantle, as well as the ionosphere and magnetosphere. —Chris Young, Interesting Engineering, 14 Nov. 2025

These storms can disrupt navigation and radio systems through ionosphere heating and induce geomagnetic currents in long-distance transmission lines or pipelines, potentially causing voltage control issues, tripping of safety equipment, and even large-scale power outages in extreme cases. —Hollie Silverman, MSNBC Newsweek, 11 Nov. 2025

Word History

Etymology

ion or ion(ization) + -o- + -sphere

Note: The term was introduced by the British engineer and physicist Robert A. Watson-Watt (1892-1973), apparently first in an unpublished letter (November 8, 1926) to the secretary of the Radio Research Board, a government agency (see Nature, vol. 224, December 13, 1969, p. 1096). Watson-Watt used it in print in the Quarterly Journal of the Royal Meteorological Society, vol. 55 (1929), p. 278.

First Known Use

1926, in the meaning defined above

Kids Definition

ionosphere

noun

ion·​o·​sphere ī-ˈän-ə-ˌsfi(ə)r 

: the part of the earth's atmosphere beginning at an altitude of about 30 miles (50 kilometers) and extending outward that contains free electrically charged particles

ionospheric

ī-ˌän-ə-ˈsfi(ə)r-ik 

-ˈsfer-

adjective