The Influence of Space Weather on the Relationship Between the Parameters TEC and foF2 of the Ionosphere

The critical frequency foF2 is an important parameter of the ionosphere, but its measurement data are often absent, especially during disturbances caused by the impact of space weather. The aim of this paper is to use the total electron content TEC to obtain foF2, which is necessary in such tasks as forecasting the maximum useable frequencies on HF paths, assimilation in the ionospheric models used in satellite wireless communication systems and for positioning. Formally, these parameters are linearly related through the equivalent slab thickness τ of the ionosphere, however, this relationship has not been practically studied for the southern hemisphere, since the thickness τ(IRI) of the International Reference Ionosphere IRI model can be used. This paper compares the efficiency of using τ(IRI) and various proposed options for determining experimental τ. The results are presented using the example of the March 2012-2017 disturbances and three stations in the southern hemisphere. Experimental medians τ(med) for a specific station in the current year and for other years, the median of another station, are used as τ. It is shown that the IRI model reacts only to negative disturbances. The use of various options for determining τ provides a 1.5-2 times better agreement with the real foF2. Especially, it concerns the long periods of enhancements of TEC (5-7 days), not connected in magnetic storms.