Information on the D- and E-region electron density profiles

The paper surveys the available information on the D- and E-region electron density profile. The behavior of the E-layer peak in time and space is fairly well mapped from ionosonde measurements. Our knowledge of the ionization distribution below the maximum of the E layer comes from a limited number of rocket flights through the lower ionosphere and from extended time series of observations by ground-based radio methods from a few stations. From such measurements a very sketchy and imperfect picture emerges of the electron density profile in the quiet and disturbed lower ionosphere and its geographical, diurnal, seasonal, and sunspot cycle variation.