Ionospheric assimilation techniques for ARGOS Low‐Resolution Airglow and Aurora Spectrograph (LORAAS) tomographically reconstructed equatorial electron density profiles

Abstract

The LORAAS instrument aboard the ARGOS satellite observes line‐of‐sight ultraviolet limb intensities from ionosphere and thermosphere airglow. This study uses tomographically reconstructed electron density profiles (EDPs) from the nightside emissions. The ionospheric reconstruction is performed using a two‐dimensional O+ 1356Å radiative recombination forward model and discrete inverse theory. The forward model assumes a Chapman layer for the vertical electron density distribution from which hmF2, NmF2, and topside scale height are derived for every 90 s limb scan, which is equivalent to 5° resolution in latitude. Since ARGOS is in a near Sun‐synchronous orbit, these EDPs form a latitude slice through the equatorial anomaly structures at approximately 0230 LT. These data reflect ongoing ionospheric processes, and it is necessary to assimilate or compare with a model that contains appropriate ionospheric evolution such as the ionospheric forecast model (IFM). This study addresses the reasonableness of both the reconstructed EDPs and the IFM in describing the equatorial anomalies' diurnal and weather variability. The comparison of the LORASS EDPs with those of IFM for October 2000 show that the EDP reconstruction results compare favorably to the IFM EDPs in peak height and topside scale height. Additionally, the sector‐to‐sector climatology of the observed and modeled equatorial anomalies is similar to within the resolution of the instrument and model. The variability observed in each pass of the satellite is much larger than the IFM variability. The LORASS observation variability indicates that careful assessment of the representation error of the observations should be addressed through supplemental observations.