Numerical representation of monthly median critical frequencies of the regular E region (foE)

Simple daytime approximations to the diurnal, seasonal, and solar activity dependence of E region critical frequencies were used to predict the propagation parameters of the E region. Frequencies, as observed by the vertical incidence ionosondes were merged with recent work on the nighttime foE to develop a numerical representation of foE continuous over the entire 24 hour period for each month at minimum and maximum solar activity levels. The use of this numerical representation is recommended whenever predictions of foE are required. Sample contour maps derived from this representation are presented.