Post-Sunset Equatorial Ionization Anomaly (EIA) merging during a weak geomagnetic activity on 23-24 February 2023*

This study explores the evolution of the post-sunset Equatorial Ionization Anomaly (EIA) following a weak geomagnetic activity on 23rd February 2023 over the American sector (65°W). The total electron content (TEC) data collected from the ground-based Global Navigation Satellite System (GNSS) receivers show merging of the EIA crest on 24 February around 02 UT, with a faster equatorward motion of the northern crest in comparison to the southern crest. This occurrence is also investigated using the Global Ionosphere Thermosphere Model (GITM), which uses Field-Aligned Currents (FACs) from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) for capturing high-latitude electrodynamics. The TEC data from GITM replicates both the observed EIA merging and its interhemispheric asymmetries (IHAs) on the 24th. The wind plots show a reduced upward ion drift between 00UT to 02UT, which partly contributes to the merging, and an asymmetric equatorward-propagating traveling atmospheric disturbance (TAD), which accelerates the equatorward movement of the NH crest. The IHAs in the TAD propagation result from IHAs in the Joule Heating (JH) deposition. Stronger Joule heating is deposited in the NH at around 00UT, which drives the NH TAD, while no evident Joule heating is deposited in the SH at the same time.