Characteristics of Longitudinal Discontinuity Over Nighttime Equatorial Ionization Anomaly Crests With Multiple Observations

Longitudinal discontinuity is observed over nighttime equatorial ionization anomaly (EIA) crests, characterized by a significant depletion between longitudes. Multiple observations, especially GOLD 135.6‐nm airglow images, are used to investigate the EIA discontinuity in details. Discontinuity events are found more likely to occur in one hemisphere, with a longitudinal width of tens of degrees and prolonged durations of several hours from 19 to 24 LT. The plasma depletion is most conspicuous at low altitudes, near or below the peak height. For the Atlantic sector, the EIA discontinuity is most prevalent between the March Equinox and the September Equinox, with an equinoctial asymmetry of higher occurrence rates around September Equinox. The climatological results indicate that field‐aligned trans‐hemispheric wind plays a predominant role in promoting the discontinuity, which transports the plasma from one hemisphere to the other hemisphere, resulting in potential localized depletion over the EIA crest. Plain Language Summary The equatorial ionization anomaly is one of the most prominent features in the low‐latitude ionosphere, with two well‐marked cumulating plasma bands parallel to the magnetic equator at approximately ±15° magnetic latitude. Usually, EIA crests are thought as continuous bands that vary with local time, season, and solar activity. In this work, with high spatial resolution GOLD nightglow images, the unexpected longitudinal discontinuities occurring over EIA crests are discussed. This newly found phenomenon is named the EIA discontinuity (EIAD) by a previous scholar, which is more likely to occur in one hemisphere, has a wide longitudinal span of tens degrees, and can persist for several hours. Based on our results, the trans‐hemispheric neutral winds might dominate the formation of the discontinuity. Winds drag plasmas moving along geomagnetic lines from one hemisphere to another hemisphere, causing localized density depletion and discontinuities in the crest region. Stronger winds could transport plasmas farther, responsible for potential discontinuities over both crests. This study could better our understanding of the low‐latitude ionosphere and improve the empirical modeling of EIA regions. Key Points Discontinuity over nighttime equatorial ionization anomaly (EIA) crests is observed from 19 to 24 LT with longitudinal depletion of tens‐degree width EIA discontinuity is prevalent from March to September in the American and Atlantic sec