Comparison between IRI-2012 and GPS-TEC observations over the western Black Sea

The ionosphere is a dynamic layer which generally changes according to radiation emitted by the sun, the movement of the earth around the sun, and sunspot activity. Variations can generally be categorized as regular or irregular variations. Both types of variation have a huge effect on radio wave propagation. In this study, we have focused on the seasonal variation effect, which is one of the regular forms of variation in terms of the ionosphere. We examined the seasonal variation over the ZONG station in Turkey for the year 2014. Our analysis results and IRI-2012 present different ideas about ionospheric activity. According to our analysed results, the standard deviation reached a maximum value in April 2014. However, the maximum standard deviation obtained from IRI-2012 was seen in February 2014. Furthermore, it is clear that IRI-2012 underestimated the VTEC values when compared to our results for all the months analysed. The main source of difference between the two models is the IRI-2012 topside ionospheric representation. IRI-2012 VTEC has been produced as a result of the integration of an electron density profile within altitudinal limits of 60-2000 km. In other words, the main problem with regard to the IRI-2012 VTEC representation is not being situated in the plasmaspheric part of the ionosphere. Therefore we propose that the plasmaspheric part should be taken into account to calculate the correct TEC values in midlatitude regions, and we note that IRI-2012 does not supply precise TEC values for use in ionospheric studies.