Validation of E‐Region Model Electron Density Profiles With AURIC Utilizing High‐Resolution Cross Sections

Abstract

E‐region models have traditionally underestimated the ionospheric electron density. We believe that this deficiency can be remedied by using high‐resolution photoabsorption and photoionization cross sections in the models. Deep dips in the cross sections allow solar radiation to penetrate deeper into the E‐region producing additional ionization. To validate our concept, we perform a study of model electron density profiles (EDPs) calculated using the Atmospheric Ultraviolet Radiance Integrated Code (AURIC; D. Strickland et al., 1999, https://doi.org/10.1016/s0022-4073(98)00098-3) in the E‐region of the terrestrial ionosphere. We compare AURIC model outputs using new high‐resolution photoionization and photoabsorption cross sections, and solar spectral irradiances during low solar activity with incoherent scatter radar (ISR) measurements from the Arecibo and Millstone Hills observatories, Constellation Observing System for Meteorology Ionosphere and Climate (COSMIC‐1) observations, and outputs from empirical models (IRI‐2016 and FIRI‐2018). AURIC results utilizing the new high‐resolution cross sections reveal a significant difference to model outputs calculated with the low‐resolution cross sections currently used. Analysis of AURIC EDPs using the new high‐resolution data indicate fair agreement with ISR measurements obtained at various times at Arecibo but very good agreement with Millstone Hills ISR observations from ∼96–140 km. However, discrepancies in the altitude of the E‐region peak persist. High‐resolution AURIC calculations are in agreement with COSMIC‐1 observations and IRI‐2016 model outputs between ∼105 and 140 km while FIRI‐2018 outputs underestimate the EDP in this region. Overall, AURIC modeling shows increased E‐region electron densities when utilizing high‐resolution cross sections and high‐resolution solar irradiances, and are likely to be the key to resolving the long standing data‐model discrepancies.

A Missing Piece of the E‐Region Puzzle: High‐Resolution Photoionization Cross Sections and Solar Irradiances in Models

“…Comparison of model outputs with observations is also necessary to verify these findings. However, further validation of the model results with incoherent scatter radar measurements and additional models is addressed in the paper by Sakib et al (2023).…”

“…Comparison of the model volume production rates using the coarse grid cross sections (BHR and LR) and the new solar spectrum on the coarse wavelength grid as inputs highlights the impact of the new cross section data while comparison of the model ionization rates using the Conway (1988) cross sections and new solar spectrum on the coarse and fine wavelength grids (LR and ILR) as inputs highlights the impact of using new high-resolution solar spectrum data alone. We find that using new high-resolution solar spectrum data binned onto the coarse wavelength grid (to match the grid of Conway, 1988) is not sufficient to resolve the discrepancies in both magnitude and shape in model and observational EDPs (Sakib et al, 2023). Similarly, utilizing high-resolution cross section data on a coarse wavelength grid (BHR) with a coarse grid solar spectrum is not sufficient.…”

“…Using updated high-resolution solar irradiances with the ILR cross sections also does not adequately resolve the data-model discrepancy. Rather, the combination of high-resolution cross sections and high-resolution solar spectra on a fine wavelength grid begins to resolve the discrepancy between the model and observational EDPs (Sakib et al, 2023). The calculations presented in the paper by Sakib et al (2023) utilize these updated high-resolution cross sections (HR cross sections) and high-resolution solar spectrum on the fine wavelength grid.…”