“…The isotropic exponential model gives a reasonable approximation to the ionospheric conductivity versus height profile through the lower ionosphere layers, and the propagation parameters of the model can be deter· mined from closed form expressions of the surface impedance [Galejs, 1961a[Galejs, , 1962a[Galejs, , b, 1964a]_ Calcu· lated resonance frequencies and Q factors that are based on (3), (4), and available values of 5 [Galejs, 1962a] are listed in tables I and II. Calculations are based on daytime or day and nighttime ionosphere models.…”