An empirical model for the ionospheric electron content at low latitude in Brazil and a comparison with IRI95 Original Research Article

Ionospheric total electron content (TEC) data obtained over Cachoeira Paulista (22.5° S, 45° W, dip angle 28° S) from measurements of Faraday rotation of VHF beacon transmission from signals transmitted by GOES 1, 2 and 3 geostationary satellites during the years 1982, 1984, 1986, 1988 and 1989 are used to develop a local empirical model for the TEC for the Brazilian low latitude. The TEC values, predicted by this local model, are compared with those calculated by the IRI95. Discrepancies between these models are found, mainly near sunrise when the IRI predictions for the morning TEC minimum, and the following sunrise increase, are ∼ 1 hour earlier than observations at all seasons and at all solar activity levels. IRI overestimates the values of TEC for all local times and seasons during solar minimum, except at winter nighttime. Disagreements are also found during afternoon hours near solar maximum with underestimated values of TEC predicted by IRI. Further more, the IRI95 does not predict the near midnight peak in TEC that arises from the equatorial anomaly.