The Present State of Knowledge concerning the Lower Ionosphere

In this paper an attempt is made to summarize the current state of knowledge concerning the lower ionosphere. This includes at D and lower E region heights: electron density as functions of height and time, dissipative processes, the possible atmospheric constituents involved and their distributions, physical parameters to be considered, and solar radiations and other factors relevant in the formation of this portion of the ionosphere. Where possible, comparisons between theory and experiment are made.