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

Abstract

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.