Basic physics of the ionosphere: a tutorial review

This paper is an exposition of the basic physics of the ionosphere, according to the present understanding. It concentrates on the large-scale ionospheric structure at heights above 100 km. Since the ionosphere depends greatly on the structure and dynamics of the neutral atmosphere from which it is formed, and on the geomagnetic field, brief descriptions of these are given. The paper then reviews the theoretical structure of the ionospheric layers and discusses the most important ionospheric phenomena. It concludes with a summary of recent progress and outstanding questions, and a bibliography for further reading.