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

This study aims to understand the evolution of post-sunset equatorial ionization anomaly (EIA) during a weak geomagnetic activity on 23-24 February 2023 in the American sector. The total electron content (TEC) measured by the ground-based Global Navigation satellite system (GNSS) receivers reveals that the post-sunset shows an early merging than the previous two days. Additionally, the northern EIA peak undergoes a more substantial equatorward movement than the southern EIA peak. The Global Ionosphere Thermosphere Model (GITM) will be used to investigate the evolution of the post-sunset EIA during this event. Specifically, field-aligned currents (FACs) from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) dataset will be utilized to drive GITM. We will compare the GITM outputs with the Global Navigation Satellite System (GNSS) TEC data to examine whether the EIA merging and their interhemispheric asymmetry can be well replicated in GITM. Furthermore, we will analyze a series of ionospheric and thermospheric parameters and conduct a term analysis to determine the major factors contributing to the merging of the peak in each hemisphere. This study will provide new insights about the cause of the post-sunset EIA merging.