STUDY OF THE EQUATORIAL IONIZATION ANOMALY ALONG 75 ° E MERIDIAN USING GPS TEC

The characteristics of the equatorial ionization anomaly (EIA) are studied by analyzing dual-frequency signals from the Global Positioning System satellites measured at 11 observational sites throughout India. Specifically, we studied the seasonal and diurnal effects of the EIA during the period April 2004 to November 2004. Results show that the magnitude of EIA exhibits a semiannual variation. The EIA crest is most developed around 1400 LT and at geographic latitude around 18°N. From two observations of sudden storms in July and November 2004, it is found that within 48 hours of sudden storm commencement the VTEC value changes significantly