The accuracy of IRI in the description of development of the equatorial (Appleton) anomaly

The accuracy of the last version of the 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 the 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.