Some Results of a New Method for Obtaining Ionospheric N (h ) Profiles and Their Bearing on the Structure of the Lower F Region

To be useful for studies of ionospheric processes, N(h) profiles must be obtainable from ionograms by methods that minimize uncertainties near the base and peak of the F region and that give the true shape of the profile with an accuracy commensurate with the available virtual height information. We present the principles of such a method, in which corrections are made for unobserved and ‘valley’ parts of the profile, and which gives a good convergence to the true curvature of the profile in each interval. Examples show a sequence of profiles calculated through the sunrise period at a midlatitude station. The E-region valley is found to range between 40 and 150 km in width.