ionosphere

A region of the atmosphere extending, approximately, from 60-80 to 500-1000 km of altitude, in which the air is ionized, such that positive ions and free electrons flow through it, which makes it behave like an electrical conductor. The ionic density is high enough for radio waves within a certain frequency range to be reflected within it. It also causes interference in the signals sent to Earth by artificial satellites. At mid-latitudes, ionization in this atmospheric region is mainly due to the absorption of certain UV and X-ray bands of solar radiation, while at high latitudes it is mainly caused by the highly energetic particles carried by the solar wind, which the Earth's magnetic field diverts toward the poles. The ionosphere presents a division into three layers, known by the initials D, E, and F. The D layer is only present during the day and is the lowest of all, being able to begin to manifest from about 60 km of altitude. Above it lies the E layer and higher still the F layer, which splits into two sublayers (F₁ and F₂) of variable thickness, depending on whether it is day or night. The main characteristics of each of the ionospheric layers are described in detail in the corresponding entries of this dictionary.