The Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM): NmF2 and hmF2

• Published in: Journal of geophysical research. Space physics 2017-08, Vol.122 (8), p.9015-9031
• Main Authors: Themens, David R., Jayachandran, P. T., Galkin, Ivan, Hall, Chris
• Format: Article
• Language: English
• Subjects: Auroral oval; Electron density; empirical modeling; E‐CHAIM; Geomagnetic latitude; Geomagnetism; High frequencies; high latitude; International Reference Ionosphere; International standards; Ionosphere; Ionospheric trough; Latitude; Perturbation methods; Polar caps; Radar; Radio occultation; Representations; Traffic flow; Traffic models
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2017JA024398

We present here the Empirical Canadian High Arctic Ionospheric Model (E‐CHAIM) quiet NmF2, perturbation NmF2, and quiet hmF2 models. These models provide peak ionospheric characteristics for a domain above 50°N geomagnetic latitude. Model fitting is undertaken using all available ionosonde and radio occultation electron density data, constituting a data set of over 28 million observations. A comprehensive validation of the model is undertaken, and performance is compared to that of the International Reference Ionosphere (IRI). In the case of the quiet NmF2 model, the E‐CHAIM model provides a systematic improvement over the IRI Union Radio Scientifique Internationale maps. At all stations within the polar cap, we see drastic RMS error improvements over the IRI by up to 1.3 MHz in critical frequency (up to 60% in NmF2). These improvements occur primarily during equinox periods and at low solar activities, decreasing somewhat as one tends to lower latitudes. Qualitatively, the E‐CHAIM is capable of representing auroral enhancements in NmF2, as well as the location and extent of the main ionospheric trough, not reproduced by the IRI. The included NmF2 storm model demonstrates improvements over the IRI by up to 35% and over the quiet time E‐CHAIM model by up to 30%. In terms of hmF2, over the validation periods used in this study, we found overall RMS errors of ~13 km for E‐CHAIM, with IRI2007 overall hmF2 errors ranging between 16 km and 22 km. The E‐CHAIM performs comparably to or slightly better than the IRI within the polar cap; however, significant improvements are found within the auroral oval. Plain Language Summary We here present a new high‐latitude representation of the peak electron density and height of the ionosphere. This new model provides quiet time representations of the peak ionospheric density and height, as well as an empirical storm time representation for the peak density. Taking advantage of new instrument deployments at high latitudes and a regional modeling approach, we see significant improvements (by 60% or more) over the current international standard for ionospheric specification, the International Reference Ionosphere (IRI). Qualitatively, the new model features a significant improvement in horizontal resolution over the IRI, where it is capable of representing auroral enhancements in peak density, as well as the location and extent of the upper midlatitude density depletion known as the main ionospheric trough (MIT). Both of these