Validation and Improvement of NeQuick Topside Ionospheric Formulation Using COSMIC/FORMOSAT-3 Data

We examine systematic differences between topside electron density measurements and different topside model formulations including alpha-Chapman, NeQuick, and an improved NeQuick (NeQuick-corr) topside formulation, recently proposed. The global topside electron density data set used, was extracted from Radio Occultation (RO) topside electron density profiles on board Low-Earth Orbit satellites from the COSMIC/FORMOSAT-3 (Constellation Observing System for Meteorology, Ionosphere, and Climate and Formosa Satellite) mission. By using RO topside electron density measurements collocated with digisonde stations, we ensure that our investigation is based on two independent data sets (RO and digisondes). A subset of these profiles, with matched (within 5%) peak RO-digisonde characteristics (foF2 and hmF2) is also exploited. This subset is exploited to extend the investigation on the basis of a higher quality validation data set. The comparison demonstrates that alpha-Chapman and NeQuick-corr underestimate, whereas NeQuick overestimates COSMIC topside electron density observations. The main outcome of this study is the significant NeQuick topside representation improvement that can be achieved near the F region peak, if the key parameter g, which controls the change of scale height with respect to altitude, is optimized to a value of 0.15 (compared to a currently adopted value of 0.125). The NeQuick-corr topside formulation using the optimized g value of 0.15 outperforms all other topside formulations.

Automated summary

By examining systematic differences between topside electron density measurements and various topside model formulations, it was found that the NeQuick-corr topside formulation performs the best, offering significant improvement near the F region peak.