Evaluation of the IRI model using CHAMP observations in polar and equatorial regions

This study compares the electron density and temperature observed by the CHAMP satellite and those predicted by the International Reference Ionosphere (IRI) model. The comparison has revealed a general agreement between CHAMP and IRI in the seasonal variation of the electron density and temperature. However, in polar regions, the model tends to overestimate the electron density and underestimate the electron temperature. In addition, the CHAMP observes a weaker winter anomaly in the southern hemisphere than in the northern hemisphere, while the IRI predictions are similar in both hemispheres. In the equatorial region, the model describes the dayside equatorial ionization anomaly fairly well, but underestimates its depth in the post-sunset local time sector by about 50%. In polar regions, two prominent spatial structures observed by CHAMP are found to be missing in the IRI prediction. Namely, a band of low electron density along the nightside auroral region and a band of elevated electron temperature near the cusp. The high-Te band near the cusp exhibits clear seasonal variation, with the largest latitude and local time coverage in summer and the smallest in winter.