Validating the performance of the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) with in situ observations from DMSP and CHAMP

The Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) is a new empirical model of high latitude ionospheric electron density. While the introductory studies regarding E-CHAIM include validations, E-CHAIM's topside model was notably excluded from independent validation using datasets not included in the model fitting. In this study, we undertake such a validation using in situ electron density observations from the Defense Meteorological Satellite Program (DMSP) constellation of satellites and the Challenging Mini-satellite Payload (CHAMP) mission. Through this validation, we show that E-CHAIM generally outperforms the International Reference Ionosphere (IRI) at DMSP orbit (~830 km altitude), with RMS errors of 8.3-9.8 × 10⁹ e/m³ versus the IRI's 1.2-1.3 × 10¹⁰ e/m³. E-CHAIM's improvement over the IRI is consistent at all latitudes but is particularly noted in sub-auroral regions and is mainly limited to summer and equinox periods. At CHAMP orbit, E-CHAIM and the IRI are found to perform largely comparably, with E-CHAIM outperforming the IRI only marginally with RMS errors of 7.11 × 10¹⁰ e/m³ versus the IRI's 7.48 × 10¹⁰ e/m³. This improvement is found to be largely constrained to sub-auroral latitudes with both models performing comparably at higher latitudes. An observed tendency for the IRI to overestimate electron density in the near-peak (at CHAMP orbit) and underestimate electron density at higher altitudes (DMSP orbit) appears to be consistent with previous work, which identified this pattern to result from shortcomings in the NeQuick topside function curvature at high latitudes.