Improved models for estimating sporadic-E intensity from GNSS radio occultation measurements

Several models for estimating sporadic-E intensity from Global Navigation
Satellite System (GNSS) radio occultation (RO) observation have previously
been developed using a single perturbation or intensity parameter, such as
phase-based total electron content (TEC) or the amplitude-based S4 index.
Here, we outline two new models that use a combination of phase and
amplitude parameters for the L1 and L2 signals. These models show a significant
improvement over the baseline models used for comparison. Furthermore,
the GNSS-RO parameters are compared with several different ionosonde
intensity parameters including the direct foEs and fbEs measurements along
with the metallic-ion based foμEs and fbμEs parameters which account for
the background E-region density. Interestingly, the phase-based σϕ scintillation
index shows the strongest correlation to foEs and fbEs while amplitude-based S4
shows the strongest correlation to foμEs and fbμEs. While the metallic-ion based
foμEs and fbμEs parameters are physically ideal for GNSS-RO observations,
we show difficulties in practical implementation due to the reliance on a
background E-region density estimate using a model such as the International
Reference Ionosphere (IRI). Ultimately, we provide two improved sporadic-E
intensity models that can be used for future GNSS-RO based studies along with
a recommendation to compare against the ionosonde-based foEs parameter.