Abstract
The measurements of ionospheric TEC (total electron content) are conducted at a low latitude Indian station Surat (21.16°N, 72.78°E Geog.), which lies under the northern crest of the equatorial anomaly in Indian region. The data obtained are for a period of five years from low to high solar activity (2010- 2014) using GPS (Global Positioning System) receiver. In this study, we report the diurnal and seasonal variation of GPS-TEC, dependence of GPS-TEC with solar activity, geomagnetic condition and EEJ strength. From the seasonal analysis, it is found that greater values of the GPS-TEC are observed during equinox season followed by winter and summer. The appearance (in the year 2011 and 2014) and disappearance (in the year 2010 and 2012) of “winter anomaly” have been observed at the station. From the correlation of GPS-TEC with different solar indices, i.e. solar EUV flux, F10.7 cm solar radio flux and Zurich sunspot number (SSN), it is concluded that the solar index EUV flux is a better controller of GPS-TEC, compared to F10.7 cm and SSN. Further, it is observed that there is no effect of rising solar activity on correlation. Moreover, the percentage variability of GPS-TEC and the standard deviation of GPS-TEC obtained for quiet and disturbed days show that dependence of GPS-TEC on geomagnetic condition is seasonal. Also, there is a positive correlation observed between GPS-TEC and EEJ strength.
Highlights
total electron content (TEC) data collected from the low solar activity to high solar activity periods between January-2010 to February-2015 at the observing station are being used
To study the Global positioning system (GPS)-TEC variation with local time, season, solar activity and geomagnetic condition, we have used a data base from January 2010 to December 2014 situated under the northern crest of the equatorial anomaly region, Surat
(IST = local time (LT) = UT + 5:30 hrs) pre-dawn to sun up period, reaching a minimum between 05:00 to 06:00 IST over the Indian sector and steadily increase with the time of day attaining a maximum in the noon to afternoon and a gradual decrease after sunset
Summary
The ionospheric plasma density in the ionosphere exhibits significant variations with time (sunspot cycle, seasonal, diurnal, latitude, longitude, solar and geomagnetic activities), which can result in change of special vital ionospheric parameters such as total electron content (TEC). The Global positioning system (GPS) signal propagating through the ionosphere is advanced in phase and delayed in time. This time delay being a function of electron density when measured by using dual frequency receiver can compute the TEC. The GPS-TEC data for the Surat station (located under the northern crest of the equatorial ionization anomaly in Indian sector) have been analyzed earlier in the year 2009 at low solar activity period [27]. We obtained correlation coefficient between GPS-TEC and solar indices, especially to the intensity of the ascending phase of the 24th solar cycle being subdued
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