Alternate Definitions for ionosphere

The region of the Earth’s upper atmosphere containing free electrons and ions produced by ionization of the constituents of the atmosphere by solar ultraviolet radiation at short wavelengths < 100nm) and energetic precipitating particles. The ionosphere influences radiowave propagation of frequencies less than about 300 MHz. (See D region, E region, F region.)

An atmospheric layer in which a small fraction of electrons have been separated from their parent ions by energetic processes. Solar photons, solar protons and auroral particles, with sufficient energy, strip the electrons to produce a weak plasma.