Predicted and measured electron density at 600 km altitude in the South American peak of the equatorial anomaly

Measurements of the electron density at 600 km altitude (N₆₀₀) were obtained with the Hinotori satellite launched by the Institute of Space and Astronautical Science of Japan. These measurements were used to check the validity of the International Reference Ionosphere (IRI) model in predicting the electron density at that altitude in the South American peak of the equatorial anomaly. The measurements correspond to the longitude zone from 285 to 369° and −15° geomagnetic latitude. To model the electron density at 600 km altitude, two cases were considered, namely (i) N₆₀₀ was calculated with the IRI model at 10° intervals within the corresponding longitudinal zone and mean values were obtained, and (ii) N₆₀₀ was calculated with the IRI using ionosonde data as input coefficients in the model. The data used for this study were measured almost simultaneously with the total electron content data used in a previous work. The results show good predictions at hours of minimum ionisation for the equinox and the December solstice. For the June solstice, the best agreement was obtained around noon. However, strong disagreements were observed in some cases such as the equinox at 15:00 LT, suggesting that there is a need to improve the modeled topside profile.