Empirical orthogonal function analysis and modeling of the ionospheric peak height during the years 2002-2011

The ionospheric peak electron density height (hm) is one of the most important ionospheric parameters characterizing high-frequency radio wave propagation conditions. In this paper, a global hm model based on the empirical orthogonal function (EOF) analysis method is constructed by using Global Navigation Satellite Systems ionospheric radio occultation measurements from COSMIC and CHAMP as well as global ionosonde data during the years 2002–2011. The variability of hm can be well represented by the several EOF base functions Ek and the corresponding coefficients Pk. The rapid convergence of EOF decomposition makes it possible to use only the first four EOFs components, which express 99.133% of total variance in this study, to construct the empirical model. The variations of hm with respect to the magnetic latitude, local time, season, and solar cycle have been studied, and the EOF-based hm model has been validated through comparisons with the International Reference Ionosphere (IRI) model and other observation. The evaluations indicate that the EOF and IRI model give better hmF₂ at middle and high latitudes than those at low latitudes. Since the limited data were used in the EOF model during high solar activity years, its accuracy degrades to some extent. During nighttime of spring, summer, and winter in the auroral zone, the hm derived from the EOF model may range from 90 to 150 km because of the reduction of hm, which is due to particle precipitation, whereas the IRI model does not include this reduction. During the periods of low solar activity, the F₂ peak heights (hmF₂) from the EOF model are in good agreement with the observed data, while the IRI model tends to overestimate the hmF₂ in the middle and high latitudes.