Accurate photoionization rates are vital for the study and understanding of ionospheres and may account for the discrepancy in electron densities and mismatched altitude profiles of current E-region models. The underestimation of electron density profiles could be mitigated by high-resolution cross sections that preserve autoionization lines which allow solar photons to leak through to lower altitudes. We present new ionization rates calculated with high-resolution (0.001 nm) O and N2 photoionization and electron impact cross sections, and a high-resolution solar spectrum as inputs to CPI’s Atmospheric Ultraviolet Radiance Integrated Code [AURIC, Strickland et al., 1999]. The new electron impact cross sections show little structure and have minimal effect on calculations of ionization rates. Results from AURIC with updated O and N2 cross sections indicate increased production rates up to ~40% in the E-region, specifically between 100–115 km. Likewise, production rates determined using the ionospheric photoionization rate code from Meier et al. [2007] also illustrate an increase in the O and N2 production rates (typically of more than 10%) when using the newly calculated cross sections. Additionally, we find that O and N2 dominate the volume production rates above 130 km while O2 is expected to be the main contributor from 95–130 km. AURIC model results that use the default data and model results with the new O and N2 cross sections both track very well with electron density profiles determined from Arecibo ISR observations. AURIC model results using the new cross section calculations are in better agreement with Arecibo observations at higher altitudes. Our current findings indicate that O2 plays a dominant role in photoionization production rates in the E-region. Therefore it is crucial to update ab initio ionospheric models with high-resolution photoionization cross sections.

Accurate photoionization rates are vital for the study and understanding of planetary ionospheres. Previous model calculations of terrestrial photoionization rates lack sufficient spectral resolution to account for highly structured photoionization cross sections as well as the solar spectral irradiance. We present new photoionization rate calculations from CPI’s Atmospheric Ultraviolet Radiance Integrated Code [AURIC; Strickland et al., 1999] using high-resolution (0.01 Å) solar spectra and high-resolution (0.01 Å) atomic oxygen (O) and molecular nitrogen (N2) photoionization cross sections. Theoretical photoionization cross sections of O are determined utilizing the R-matrix plus pseudo-states (RMPS) approximation whereas N2 cross sections are determined using the R-matrix approximation. We include 34 high-resolution partial O state photoionization cross sections and 3 high-resolution partial N2 state photoionization cross sections with supplemental Conway [1988] tabulations for molecular oxygen and the remaining N2 states. We find that photoionization rates computed at 0.01 Å resolution differ substantially from rates computed using low-resolution cross sections, especially in the lower thermosphere below 200 km. Specifically, we find that ionization production rate ratios exhibit variations in altitude of more than ±40% between the high- and low-resolution cases. Past low-resolution calculations at various low spectral resolutions do not sufficiently account for or preserve the highly structured auto-ionization lines in the photoionization cross sections [Meier et al., 2007]. These features, in combination with high-resolution solar spectra, allow photons to penetrate deeper into the Earth’s atmosphere producing larger total ionization rates. These higher ionization rates may finally resolve data-model discrepancies in altitude profiles of electron densities due to the use of low-resolution photoionization cross sections in current E-region models.