Features of Pronounced Longitudinal TEC Differences at Low and Middle Latitudes Over the South American Sector

Longitudinal structuring of the ionosphere reflects the coupled neutral and electrodynamic processes that shape regional plasma transport and space weather variability; however, its behavior at low–midlatitudes remains incompletely understood. Here we investigate longitudinal variations in ionospheric total electron content (TEC) over South America during the 2020–2021 solar minimum using ground‐based Global Navigation Satellite System observations, COSMIC‐2 radio occultation data, and ICON in situ measurements. We identify a previously unreported diurnal east‐west differential structure extending across low‐ and midlatitudes during local summer (November–February). The observed pattern exhibits a three‐phase evolution: enhanced daytime TEC in the western sector before local noon, a post‐noon to sunset reversal with higher TEC in the eastern sector, and a subsequent return to western dominance. Simulations from the Horizontal Wind Model 14 reproduce the TEC structure near noon and after sunset but show opposite behavior in the early morning, indicating that neutral wind forcing alone cannot account for the observations. Multi‐instrument analysis further reveals that longitudinal gradients in electric fields and field‐aligned diffusion contribute significantly to the TEC asymmetry. These results demonstrate that low‐midlatitude longitudinal TEC variations over South America arise from the interplay of multiple physical mechanisms and exhibit substantially greater complexity than their midlatitude counterparts, highlighting the need to incorporate coupled neutral and electrodynamic processes in regional ionospheric modeling and space weather prediction.