The Earth's Ionosphere

The ionosphere is the portion of the Earth's atmosphere which has been partially ionised by solar radiation.  Radiation at ultra violet and shorter wavelengths is capable of ionizing atoms in the high atmosphere, turning this neutral gas into a partially ionised plasma.  This occurs from heights above 90km with the peak in the electron density occuring at typically 300km.

Studies of the ionosphere are of practical importance since of radio waves passing through an ionised gas are delayed and refracted. 

The ionosphere is important for GPS navigation. The accuracy of single frequency GPS positioning is limited by our knowledge of the total electron content along the ray path from the satellite to the receiver.  Furthermore, small scale structures causing scintillation of the radio signal can result in loss of lock onto the satellite degrading the system performance.