Abstract Several parameters, critical frequency foF2, total electron content (TEC), F2 layer peak height hmF2, and slab thickness τ are measured with a Digisonde 256 and compared with IRI 2001 predictions for Tucuman during quiet days in 2003. The comparisons between experimental and predicted diurnal curves for different seasons show a strong dependence on local time and season. Major departures are observed in autumn for all four parameters, and in slab thickness for all four seasons for this equatorial anomaly location.