The ionospheric electron content (IEC) measured using the VHF Radio Beacon (RB) technique from a geostationary satellite at Guwahati (geographic latitude 26.2"N, geographic longitude 91.7"E, geomagnetic latitude 15.2"N, dip angle 37'N, magnetic latitude 20.64"N), during low and high solar activity periods is analysed to examine the influence of solar activity on the IEC near the equatorial ionospheric anomaly crest region, and to assess the predictability of existing ionospheric models such as the International Reference Ionosphere (IRI) and the Semi empirical Low latitude Ionosphere Model (SLIM) on the IEC for different solar activity conditions.
The paper shows that the IEC figures derived from models vary widely with solar activity and neither of the models predicts the IEC (within its maximum and minimum deviations) at this station for the entire day. The attempt here is to explain the discrepancy observed between the measured IEC and that derived through the IRI or SLIM models, with the help of the Sheffield University Plasmasphere
Ionosphere Model (SUPIM) for a selected solar activity condition. Model IEC values computed from the IRI over a few other anomaly crest stations are also compared; the paper highlights the differences in the observed and model-predicted patterns between 20" and 25"N magnetic latitude. '