Abstract
<p>The present study investigates the variation of Total Electron Content (TEC) using Global Positioning System (GPS) satellites from four equatorial to mid-latitudes stations over a period of one year. The stations are Port Blair (11.63°N, 92.70°E), Agartala (23.75°N, 91.25°E), Lhasa (29.65°N, 91.10°E) and Urumqi (43.46°N, 87.16°E). The diurnal, monthly and seasonal variations of TEC have been explored to study its latitudinal characteristics. Analysis of TEC data from these stations reveals the characteristics of latitudinal variation of Equatorial Ionospheric Anomaly (EIA). To validate the latest IRI 2012 model, the monthly and seasonal variations of GPS-TEC at all the four stations have been compared with the model for three different topside options of electron density, namely, NeQuick, IRI-01-corr and IRI-2001. TEC predictions from IRI-2001 top side electron density option using IRI 2012 model overestimates the observed TEC especially at the low latitudes. TEC from IRI- NeQuick and IRI-01-corr options shows a tendency to underestimate the observed TEC during the day time particularly in low latitude region in the high solar activity period. The agreement between the model and observed values are reasonable in mid latitude regions. However, a discrepancy between IRI 2012 derived TEC with the ground based observations at low latitude regions is found. The discrepancy appears to be higher in low-latitude regions in comparison to mid latitude regions. It is concluded that largest discrepancy in TEC occur as a result of poor estimation of the hmF2 and foF2 from the coefficients.</p>
Highlights
The temporal and spatial variation of Total Electron Contents (TEC) at the equatorial and low latitude regions are significant compared to mid latitude regions
The model TEC data from IRI model 2012 has been taken for the same locations and time in to compare with the TEC data obtained from Global Positioning System (GPS) receiver
TEC variation at all the stations show typical diurnal characteristics such as TEC minimum at predawn and continuing increase with local sunrise attaining a maximum at local noon time followed by a decrease to a minimum during nighttime
Summary
The temporal and spatial variation of Total Electron Contents (TEC) at the equatorial and low latitude regions are significant compared to mid latitude regions. This dynamic nature is due to various processes like equatorial ionization anomaly (EIA), Equatorial Electrojet (EEJ), and equatorial spread-F (ESF) irregularities etc. TEC is an important ionospheric parameter which is defined as the total number of electrons present within an area of 1m2 cross section along the integrated path from the satellite to the receiver. The TEC study is important as this parameter helps to reveal the variability of ionospheric behavior during the solar quiet and disturbed days and has significant practical applications in satellite navigation, time delay and range error corrections for single frequency GPS satellite signal receivers
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