Imaging of the Daytime Ionospheric Equatorial Arcs With Extreme and Far Ultraviolet Airglow

We present the first global images of the daytime ionosphere equatorial arcs as manifested in the 83.4-nm airglow. These images were collected by the Limb-Imaging Ionospheric and Thermospheric Extreme-Ultraviolet Spectrograph that commenced operations on the International Space Station in early 2017. We compare these to simultaneous images of the ionospheric radiative recombination airglow at 135.6 nm measured between 250- and 350-km tangent altitudes, where the emission is generated primarily by radiative recombination of ionospheric plasma. We find that these signatures of the dense crests of the Equatorial Ionization Anomaly, their symmetry, and daily variability at 1300-1600 LT over 1-6 April 2017 do not show any strong periodicity during this time. These results are also important to the joint interpretation of these two correlated extreme and far ultraviolet emission features measured under solar minimum conditions and the evaluation of absorption and radiative transfer effects that affect these emissions differently.