Abstract
AbstractThe 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.
Highlights
Two phenomena in the low and mid latitude ionosphere — the equatorial ionization anomaly (EIA) and the irregularities that occur within them — have been the subject of decades of research, because they are a critical aspect of ionospheric variability, and have significant effects on communications and navigation systems
We found that gaps in the anomaly are observed much more frequently in these observations than in previous space-based observations
On the equatorward edges of the Equatorial Ionization Anomaly (EIA) the depletions appear as indentations; the absence of emission from these areas are indicative of depletions in the plasma, produced by instabilities that form and rise through the crests, expanding to higher magnetic latitudes as they grow
Summary
During geomagnetically quiet solar minimum conditions, significant temporal and spatial variability is observed in the equatorial ionosphere. At solar minimum, depleted ionospheric regions are observed on most nights, at varying longitudes, and with evident meridional symmetry. Synoptic-scale disruptions of the ionization crests are seen on several nights, possibly associated with large-scale plasma instabilities. During geomagnetically quiet solar minimum conditions, significant temporal and spatial variability is observed in the equatorial ionosphere. At solar minimum, depleted ionospheric regions are observed on most nights, at varying longitudes, and with evident meridional symmetry. Synoptic-scale disruptions of the ionization crests are seen on several nights, possibly associated with large-scale plasma instabilities. This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record.
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