Global Maps of foF2 Derived from Observations and Theoretical Values

Observations of the F2-region critical frequency, foF2, and values determined from the time-dependent continuity equation for ions and electrons in the ionosphere have been used to develop a new set of numerical coefficients to represent the global variation of foF2. The coefficients developed in this study, like those in earlier investigations, permit monthly median hourly values of foF2 to be obtained at any location around the globe for any month of the year and solar activity level. The procedures undertaken to develop the new numerical coefficients are described in this report. Comparisons between foF2 determined using older sets of numerical coefficients and foF2 determined using the new set of coefficients are given along with a description of how well each set of coefficients specifies and predicts the observed variations in the F2- region critical frequency.