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Abstract We investigated the effects of storm‐time diffuse auroral electron precipitation on ionospheric Pedersen and Hall conductivity and conductance during the CME‐driven St. Patrick's Day storms of 2013 (minDst = −131 nT) and 2015 (minDst = −233 nT). These storms were simulated using the magnetically and electrically self‐consistent RCM‐E model with STET modifications, alongside the B3C auroral transport code to compute ionospheric conductivities and height‐integrated conductance. The simulation results were validated against conductance inferred from Poker Flat Incoherent Scatter Radar (PFISR) and Millstone Hill Incoherent Scatter Radar (MHISR) measurements. Our simulations show that the magnetic latitude and local time distribution of Pedersen and Hall auroral conductance strongly correlate with diffuse electron precipitation flux, with the plasmapause marking the low‐latitude boundary of conductance. Simulated Pedersen/Hall conductance agrees reasonably well with PFISR measurements at 65.9° MLAT during diffuse auroral precipitation. During the intense 2015 storm, diffuse aurora extended down to 52.5° MLAT, with simulated conductance agreeing within a factor of two with MHISR observations. Discrete auroral arcs observed during both storms enhanced PFISR conductance by tens of siemens, though these enhancements were not captured by the model. Additionally, the simulated electric intensity showed development of sub‐auroral polarization streams (SAPS) and dawn SAPS features and followed the general trend of Poker Flat electric intensity at 65.9° MLAT during diffuse aurora, despite being updated every 5 min. The overall agreement between simulated ionospheric conductance and electric intensity with observations highlights the model's capability during diffuse auroral precipitation. 

Abstract The ionospheric O⁺number density can be measured remotely during the day by observing its optically thick 83.4 nm radiance. Some ambiguity is present in the process of retrieving the density due to uncertainties in the initial excitation rate. This can be removed by observing a companion optically thin emission at 61.7 nm originating from the O⁺(3s²P) state, providing that the ratio of the initial excitation rates is known. Analyses of ICON EUV data using an 83.4/61.7 emission ratio of order 10 result in O⁺densities lower by ∼2 than other measurements. Key to relating the two emissions is accurate knowledge of the partial photoionization cross sections and the spectroscopy of O⁺—the topic of this paper. Up to now, no independent evaluation of the ratio of the 83.4/61.6 emission ratio exists. The recent availability of state‐of‐the‐art calculations of O partial photoionization cross sections into a variety of O⁺states presents an opportunity to evaluate the O⁺(2p⁴⁴P)/O⁺(3s²P) ionization rate ratio. We calculate excitation of these parent states of the emissions including both direct and cascade excitation from higher lying O⁺energy states. The resulting theoretical prediction gives ratios that range from 13.5 to 12 from solar minimum to maximum, larger than the value of 10 used by the ICON 83.4 and 61.7 nm algorithm. The higher theoretical values for the ratio reconcile the ∼2 discrepancy between simultaneous ICON and other electron density measurements. 

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. 

Abstract Current and previous thermospheric remote sensing missions use N₂Lyman‐Birge‐Hopfield (LBH) band dayglow emission measurements to retrieve line‐of‐sight thermospheric composition and temperature. The precision of thermospheric composition and temperature retrieved from observations depends on the uncertainty in the relative LBH vibrational populations. In the laboratory, electron impact induced LBH emission measurements have shown that the relative vibrational populations change with gas pressure. However, it is not fully understood how these populations change for dayglow observations where the emissions that contribute to the observations vary with solar illumination and line‐of‐sight geometry. We quantify the relative vibrational populations as a function of solar zenith angle (SZA) and tangent altitude using Global‐scale Observations of Limb and Disk mission's LBH dayglow observations. We find that, while some lower vibrational levels show potential enhancement with increasing pressure (decreasing altitude), in general, they do not change significantly with SZA or tangent altitude for dayglow observations. The vibrational populations can thus be assumed as fixed parameters when retrieving neutral disk temperatures from remotely sensed LBH dayglow observations.