Ionospheric temporal variations over the region of Turkey: a study based on long-time TEC observations

In this study, daily mean vertical total electron content (VTEC) and daily mean 2-h VTEC values were obtained from Center for Orbit Determination in Europe–Global Ionosphere Maps (CODE–GIM) data over the region of Turkey between January 1, 2003, and December 31, 2016. The time interval is sufficient to reflect temporal changes of the ionosphere. The daily mean VTEC data was used to analyze the space weather effects on the VTEC variability and daily mean 2-h VTEC data was utilized to see the pattern of the diurnal, monthly, seasonal and yearly variation of VTEC values. The highest correlation was found between VTEC and F10.7 (r = 0.83). Totally, 40 major geomagnetic storms were identified that 45% of the storms are caused a decrease and 55% of the storms are caused an increase in VTEC variation. The maximum VTEC is shown at 13:00 LT and the minimum VTEC is shown at 03:00 LT according to diurnal variation of the 14-year mean 2-h VTEC. The maximum VTEC is shown on April and the minimum VTEC is shown on July according to diurnal variation of monthly mean VTEC. Diurnal variation of seasonal mean VTEC and its standard deviations are higher in equinox than solstices. Diurnal variation of yearly mean VTEC has a significant change from low to high solar activity periods.