Forecasting the Propagation of HF Radio Waves Over Bulgaria

Abstract

A new methodology for forecasting the propagation of HF radio waves by reflection from the ionosphere over Bulgaria in the absence of ionosonde data is presented. The proposed methodology contains three main parts. Based on the long-term ionosonde data an empirical model of the critical E region frequency (foE) has been built; the latter depends on the season, local time and the level of solar activity described by the solar radio flux at 10.7 cm wavelength (F10.7). The critical frequency of the F2-layer (foF2) and the maximum usable frequency at a propagation of 3000 km (MUF3000) are obtained by means of the proposed empirical relationships between these two critical frequencies and the Total Electron Content (TEC). Based on these three ionospheric characteristics a modeled electron density profile is compiled by using the method of Di Giovani-Radicella (Giovanni and Radicella in Adv Space Res 10:27–30, 1990 [1]). The constructed in this way electron density profile allows calculating the lowest and maximum usable frequency at a given distance up to 500 km according to the theory of radio wave propagation in the ionospheric plasma, namely the equivalence theorem and the secant law, as well as the law of reduction of the group velocity of propagation depending on the ionosphere electron density.