Global empirical model of critical frequency of the ionospheric F2-layer for quiet geomagnetic conditions

Using the foF 2 database obtained from satellites and ground-based ionospheric stations, we have constructed a global empirical model of the critical frequency of the ionospheric F 2-layer (SDMF2—Satellite and Digisonde Data Model of the F 2 layer) for quiet geomagnetic conditions ( Kp < 3). The input parameters of this model are the geographical coordinates, UT, day, month, year, and the integral index F 10.7 ( day , τ = 0.96) of solar activity for a given day. The SDMF2 model was based on the Legendre method for the spatial expansion of foF 2 monthly medians to 12 in latitude and 8 in longitude of spherical harmonics. The resulting spatial coefficients have been expanded by the Fourier method in three spherical harmonics with respect to UT. The effect of the saturation of critical frequency of the ionospheric F 2-layer at high solar activity was described in the SDMF2 model by foF 2 as a logarithmic function of F 10.7 ( day , τ = 0.96). The difference between the SDMF2 and IRI models is a maximum at low solar activity as well as in the Southern Hemisphere and in the oceans. The testing on the basis of ground-based and satellite data has indicated that the SDMF2 model is more accurate than the IRI model.