Abstract
Both ground- and satellite-based airglow imaging have significantly
contributed to our understanding of the low-latitude ionosphere,
especially of the morphology and dynamics of the equatorial ionization
anomaly (EIA). The NASA Global-scale Observations of the Limb and Disk
(GOLD) mission focuses on far-ultraviolet airglow images from a
geostationary orbit at 47.5°W. This region is of particular interest at
low magnetic latitudes because of the high magnetic declination (i.e.,
about -20°) and proximity of the South Atlantic magnetic anomaly.
Nighttime airglow images from GOLD reveal an exciting feature of the
EIA. Using observations from 5 October 2018 to 30 June 2020, we
characterize a wave-like structure of few thousands of kilometers seen
as poleward and equatorward displacements of the nighttime EIA-crests.
Initial analyses show that the mesoscale structure is symmetric about
the dip equator and appears nearly stationary with time over the night.
In quasi-dipole coordinates, maxima poleward displacements of the
EIA-crests are seen at about ±12° latitude and around 20° and 60°
longitude (i.e., in geographic longitude at the dip equator, about 53°W
and 14°W). The wave-like structure presents typical zonal wavelengths of
about 6.7x10^3 km and 3.3x10^3 km. The structure’s occurrence and
wavelength are highly variable on a day-to-day basis with no apparent
dependence on geomagnetic activity. In addition, a cluster or
quasi-periodic wave train of equatorial plasma depletions (EPDs) is
often detected within the mesoscale structure. We further outline the
difference in observing these EPDs from FUV images and in situ
measurements during a GOLD and Swarm mission conjunction.