The Accuracy of IRI in the Description of Development of the Equatorial (Appleton) Anomaly

An accuracy of the last version of International Reference Ionosphere IRI-2001 at low latitudes is tested by a detailed comparison of longitudinal variations in the equatorial anomaly development following from this model with the ones given by independent ISS-b satellite data. The critical frequency of F2-layer was calculated by either CCIR or URSI submodel, both of which are incorporated into IRI-2001. The main conclusion of our analysis is that the longitudinal variations given by CCIR are substantially oversmoothed in comparison with the ISS-b satellite data, and the variations given by URSI are further smoothed with respect to the CCIR ones. Therefore, further improvements of model description of the low-latitude F2-layer are desirable.