The ionosphere is a layer of the Earth’s upper atmosphere that is in the range of 80 to 600 kilometers above the surface of the planet. This range corresponds to the entire thermosphere and also a portion of the mesosphere below it.
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In this part of the atmosphere, the molecules and atoms present are subject to extreme ultraviolet radiation — waves in the range of 10 to 120 nanometers, while ultraviolet-A, which reaches us, is between 315 and 400 nanometers — and to X-rays from of the sun. This radiation is highly ionizing, that is, it has enough energy to remove electrons from an atom.
Therefore, this layer has a high density of circulating ions and electrons, which affects the propagation of radio waves and satellite signals.
Features of the ionosphere
The ionosphere has three distinct regions, called D (up to 95 km altitude), E (between 95 and 140 km, approximately) and F (from 140 to about 600 km, but these limits can vary) . The F layer can still have, at least, subdivisions: with the F1, up to the range of 300 to 400 km of altitude while the F2 goes up to 600 km. The F3 layer is not permanent and studies report its formation mainly in equatorial regions. Considering this last sublayer, the ionosphere can reach an altitude of 1000 km.
The distribution of ions and electrons along these layers is not uniform. It varies because the intensity of solar radiation is attenuated with distance, but at the same time, the atmosphere becomes thinner with altitude.
It is also important to note that, as ionization depends mainly on solar radiation (cosmic rays also ionize, to a lesser extent, the Earth’s atmosphere), the concentration of the ionosphere decreases during the night. Only the F2 layer remains with a high number of electrons in this period.
The importance of the ionosphere for telecommunications
The charged particles present in the atmosphere interact in two different ways with the waves emitted by the telecommunications systems: they reflect or refract the signals and this has both positive and negative implications.
Long-distance transmission of short-wavelength waves is only possible because of reflection provided by the ionosphere. On the other hand, the signals may undergo slight path deviations due to irregularities in the distribution of electrons and the influence of the magnetic field created by them. These two phenomena are called, respectively, ionospheric scintillations and Faraday rotation.