Resolving E-region data/model discrepancies: The role of high-resolution
cross sections and photoionization rates
Abstract
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.