Abstract
Abstract. 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 mid-latitude regions, and we note that IRI-2012 does not supply precise TEC values for use in ionospheric studies.
Highlights
GPS systems have been used in many scientific studies in recent years
When all figures are examined, it can be clearly seen that the IRI-total electron content (TEC) values produced nearly the same response in terms of monthly ionospheric activity
The changes in the obtained TEC values from IRI-2012 and Bernese 5.2 were statistically analysed for each month to monitor seasonal variations over the ZONG station in Turkey
Summary
GPS satellites send signals to receivers on L1 and L2 carrier frequencies. The carrier frequencies connecting satellites to receivers are exposed to various factors that can change the GPS signal, which can result in positioning errors. One of the positioning error sources is the ionospheric layer. The total electron content (TEC) is an important parameter that provides information about ionospheric activity. TEC is calculated along the path from the receiver to the satellite in a column with a cross-sectional area of a square metre and is expressed as TECU 1016 e/m2 (Chakraborty et al, 2014; Coley et al, 2014; Otsuka et al, 2002; Rama Rao et al, 2006; Schmidt et al, 2008; Spogli et al, 2013; Yildirim et al, 2016)
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