Global-Scale Observations of the Equatorial Ionization Anomaly

The National Aeronautics and Space Administration Global-scale Observations of the Limb and Disk ultraviolet spectrograph has been imaging the equatorial ionization anomaly (EIA), regions of the ionosphere with enhanced electron density north and south of the magnetic equator, since October 2018. The initial 3 months of observations was during solar minimum conditions, and they included observations in December solstice of unanticipated variability and depleted regions. Depletions are seen on most nights, in contrast to expectations from previous space-based observations. The variety of scales and morphologies also pose challenges to understanding of the EIA. Abrupt changes in the EIA location, which could be related to in situ measurements of large-scale depletion regions, are observed on some nights. Such synoptic-scale disruptions have not been previously identified. Plain Language Summary In this study, ultraviolet images of emissions from the Earth's nighttime ionosphere were examined to determine the location of the equatorial ionization anomaly, regions of enhanced ionization that result in bands of nighttime airglow emission that typically appear parallel to the magnetic equator near +15 degrees and -15 degrees magnetic latitude. We found that gaps in the anomaly are observed much more frequently in these observations than in previous space-based observations. These gaps, sometimes referred to as ionospheric bubbles or depletions, are important because they are associated with ionospheric changes that can cause disruptions in communications and satellite navigation that depend on satellites, such as GPS. The location of the anomaly was also observed to vary significantly, by as much as 15 degrees, from the typical latitudes. The observed level of variability seen during the unusually quiet geomagnetic conditions during which the observations occurred suggests that accurate predictions of the location and variability of the equatorial ionization anomaly requires significant advances in understanding the causes of this variability.