Characterization of Longitudinal Patterns in the Daytime Ionosphere with ICON EUV Airglow

The NASA Ionospheric Connection Explorer Extreme Ultraviolet spectrograph, ICON EUV, images one-dimensional altitude profiles of the daytime EUV airglow between 54-88 nm. This spectral range contains several OII emission features derived from the photoionization of atomic oxygen by solar EUV. The primary target of the ICON EUV is the bright OII (⁴P – ⁴S) triplet emission at 83.4 nm that is used in combination with a dimmer but complementary feature (²P – ²D) at 61.7 nm that are jointly analyzed to determine the best-fit solution of ionospheric O⁺ density profile between 150-450 km. From this result, the daytime ionospheric F-region peak electron density and height, NmF2 and HmF2 respectively, are inferred. The low-inclination orbit allows measurements across all local times, but also has a precession rate such that low and equatorial latitudes are sampled at all times over a 48-day period. This paper presents observations of the global patterns in ionospheric HmF2 and NmF2 obtained from the first two years of ICON EUV measurements, which occurred during solar minimum conditions, specifically examining longitudinal patterns in these parameters in a fixed local time frame with respect to the persistent longitudinal wave-4 features created by waves in the lower atmosphere.