IONOSPHERE

n. part of the outer atmosphere which contains large amounts of ions and free electrons (surrounds the earth and some planets)

The ionosphere is the uppermost part of the atmosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth. It is located in the Thermosphere.
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Noun
1. the outer region of the Earth's atmosphere; contains a high concentration of free electrons
(hypernym) region, part
(part-holonym) atmosphere, air
(part-meronym) D-layer, D region

n. ionosphere, part of the outer atmosphere which contains large amounts of ions and free electrons (surrounds the earth and some planets)

That part of the atmosphere, extending from about 70 to 500 kilometers, in which ions and free electrons exist in sufficient quantities to reflect and/or refract electromagnetic waves. [After JP1 ]