Comparison of GOLD Nighttime Measurements With Total Electron Content: Preliminary Results

The National Aeronautics and Space Administration (NASA) Global-scale Observations of the Limb and Disk (GOLD) has been imaging the thermosphere and ionosphere since October 2018. It provides continuous measurements over a large area from its geostationary orbit. The unambiguous two-dimensional (2-D) maps of OI 135.6 nm radiance retrieved from GOLD after sunset are compared with the total electron content (TEC) maps measured by GPS receivers in the American sector. The OI 135.6 nm radiance observed by GOLD is an indicator of the peak electron density of the ionosphere F2 region, while the TEC is the total electron density in the column. Our comparisons show that the two data sets match each other very well in the equatorial ionization anomaly (EIA) morphology and its seasonal variability. Equatorial plasma bubbles (EPBs) are evident in GOLD nighttime OI 135.6 radiance. Corresponding depletions are shown in TEC maps, but without GOLD data as a reference, it is difficult to discern that the depletions are EPBs. In addition, both GOLD 135.6 radiance and TEC maps observed third peaks of electron density poleward of the southern EIA crests. Furthermore, both show that the ionosphere after sunset is quite dynamic and has strong day-to-day variability. In all, the GOLD and TEC have valuable synergy to allow us to gain a better understanding of the equatorial ionosphere.