Early Morning Equatorial Thermosphere-Ionosphere Anomaly

During geomagnetically quiet conditions, spatial variations of early morning ionosphere-thermosphere system are mainly governed by dynamics. To study the dynamical coupling, here we investigate early morning Equatorial Ionosphere Anomaly (EIA) using Global-scale Observations of the Limb and Disk (GOLD) measurements of OI-135.6 nm nightglow emission and global positioning system (GPS) based Total Electron Content (TEC) maps. Most of the structures (about 80%) in the OI-135.6 nm emission over the American longitudes resemble, spatially and temporally, with structures observed in the GPS-TEC maps. The remaining cases, where the structures seem to differ, suggest that either the majority of electrons in TEC are not from the peak of ionospheric F-layer or F-layer is very broad or the OI-135.6 nm emissions are not produced from radiative (O⁺+e^- → O + photon) recombination. We observe that the emissions in early morning EIA crests are stronger, well separated in latitude, and mostly located over the middle of South America during October-November. In February-April months the crests are weaker, less separated in latitude, and predominantly located over the west coast (Peruvian) sector of South America. The fact that the early morning EIA is mostly located over a very limited longitude sector as seen over South America makes it unique and warrants a physical explanation. This study investigates the role of lower atmospheric tides and F-region dynamics in the evolution of the early morning EIA using Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension with Data Assimilation Research Testbed (WACCMX+DART) simulations. Further, the GPS-TEC and assimilated data will also be used for investigation of such early morning EIA at other longitudes.