Investigation of GPS-TEC Inconsistency and Correlation with SSN, Solar Flux (F10.7 cm) and Ap-index during Low and High Solar Activity Periods (2008 and 2014) Over Indian Equatorial Low Latitude Region

The ionosphere Total Electron Content (TEC) measurement using Global Positioning System (GPS) technology (GPS-TEC) is carried out over the equatorial low latitudes of Indian region viz; Bangalore $\left(13.0^{0}\mathrm{~N}, 77.5^{0}\mathrm{E}\right)$, Hyderabad $\left(17.5^{0} \mathrm{~N}, 78.5^{0} \mathrm{E}\right)$, Bhopal $\left(23.0^{0} \mathrm{~N}, 77.2^{0} \mathrm{E}\right)$, Delhi $\left(28.7^{0} \mathrm{~N}, 77.2^{0} \mathrm{E}\right)$, Ahmedabad $\left(23.0^{0} \mathrm{~N}, 72.5^{0} \mathrm{E}\right)$ and Guwahati $\left(26.0^{0} \mathrm{~N}, 92.0^{0} \mathrm{E}\right)$ for low solar activity (LSA i.e., 2008) and high solar activity (HSA i.e., 2014) periods of solar cycle 24. The measured GPS-TEC were analysed to report diurnal, day to day and monthly variation with equatorial low latitude, solar activity and geomagnetic conditions. Moreover, GPS-TEC variation is investigated to find the correlation with Sun Spot Number (SSN), Solar Flux (F10.7 cm) and Ap-index. From the results, it is found that the TEC is enhanced during HSA (2014) compared to LSA. However, depletion is observed during pre-sunrise hours (4:00 hrs. to 6:00 hrs.) particularly in spring and autumn equinox periods of HSA (2014). Also, found that the equatorial ionization anomaly (EIA) crest which is occurred over Bhopal region during LSA (2008) is shifted to the higher latitudes (i.e. Delhi region) during HSA period (2014). Further, it is observed that Ap-index and F10.7 cm have the better correlation with GPS-TEC compared to SSN for both LSA (2008) and HSA (2014) periods. Additionally, it is also observed that the increased solar activity has negative impact on correlation between GPS-TEC and Ap-index and F10.7 cm.