Ionospheric variability at Brazilian low and equatoriallatitudes: Comparison between observations and IRI model Original Research Article

Ionospheric data over two stations in Brazil, one at the magnetic equator and the other close to the southern crest of the equatorial ionization anomaly, during high and low solar activity periods were analyzed. The monthly mean of the parameters ƒoF2 and hmF2 are calculated and compared with the IRI model. The highest discrepancies are observed on post-sunset and nighttime values of ƒoF2 and hmF2 parameters over the equatorial station São Luís (2.6°S, 44.2°W, dip angle: −0.5°). In general IRI underestimates hmF2 and overestimates hmF2 at the magnetic equatorial station. The effects of post-sunset enhancement of the F-region vertical drift and the resulting intensification of the equatorial ionization anomaly are much stronger in the observation than IRI. The bottomside thickness parameter Bo is also calculated and compared with those used in IRI model.