GPS based TEC measurements for a period August 2008– December 2009 near the northern crest of Indian equatorial ionospheric anomaly region

Abstract

In recent years, measurements of total electron content (TEC) have gained importance with increasing demand for the GPS-based navigation applications in trans-ionospheric communications. To study the variation in ionospheric TEC, we used the data obtained from GPS Ionospheric Scintillation and TEC monitoring (GISTM) system which is in operation at SVNIT, Surat, India (21.16°N, 72.78°E) located at the northern crest of equatorial anomaly region. The data collected (for the low sunspot activity period from August 2008–December 2009) were used to study the diurnal, monthly, seasonal semi-annual and annual variations of TEC at Surat. It was observed that the diurnal variation at the region reaches its maximum value between 13:00 and 16:00 IST. The monthly average diurnal variations showed that the TEC maximizes during the equinox months followed by the winter months, and are lowest during the summer months. The ionospheric range delay to TEC for the primary GPS signal is 0.162 m per TECU. The diurnal variation in TEC shows a minimum to maximum variation of about 5 to 50 TECU (in current low sunspot activity periods). These TEC values correspond to range delay variations of about 1 to 9 m at Surat. These variations in the range delay will certainly increase in high sunspot activity periods. Detected TEC variations are also closely related to space weather characterizing quantities such as solar wind and geomagnetic activity indices.