Error Analysis on Nmf2 Predicted by Iri-2016 Model During Geomagnetic Quiet and Storm Periods

The International Reference Ionosphere (IRI) is an ionospheric empirical model established by assimilation and fusion of different kinds of ionospheric observation data, which can provide ionospheric parameters such as NmF2, hmF2, TEC in the range of 50-2000 km given a specified position and time. Accuracy verification of the model can provide an important scientific reference for its accuracy improvement and a priori condition for its subsequent applications. In this work, the NmF2 observed by the Global Navigation Satellite System (GNSS) occultation sounder (GNOS) mounted on FY3C(FY3C/GNOS) during geomagnetic quiet and storm periods are compared with the corresponding predictions of IRI-2016 to evaluate the error characteristics of the IRI-2016 model. After the comparison of median values of NmF2 in 9°×18° grids, we get that IRI-2016 model overestimates NmF2 compared to those of FY3C/GNOS no matter in quiet period or storm period. The biases of NmF2 relative errors between IRI-2016 and FY3C/GNOS are 10.02% and 26.88% in quiet and storm period, respectively. The results indicate the precision consistency between IRI-2016 and FY3C/GNOS in quiet period and the accuracy decrease of IRI-2016 in storm period. We also find that the NmF2 prediction accuracy of IRI-2016 at daytime are better than that at nighttime in both quiet and storm period, which is probably due to the absence of strong daytime photochemical control in F2 layer at nighttime and the time-varying ionospheric plasma irregularities after midnight.