Nocturnal Sporadic Cusp-Type Layer (Esc) Resulting From Anomalous Excess Ionization Over the SAMA Region During the Extreme Magnetic Storm on 11 May 2024

Digisonde data showed a peculiar behavior in the nighttime lower ionosphere over Cachoeira Paulista (CXP, 22.7°S, 45°W, dip ∼35°), a low-latitude station located inside the South American Magnetic Anomaly (SAMA) during the main phase of the extreme magnetic storm on 11 May 2024. The E region appeared in observational data at high altitudes after sunset, which is unexpected. In sequence, it performed an unusual descending movement due to the disturbed electric field. The extra ionization responsible for forming the nocturnal E layer is due to the precipitation (EPP) of low energic (<30 keV) particles. Moreover, a diurnal cusp-type Es layer (Es_c) appeared simultaneously, which has never been reported in the literature at such hours. Thus, the results further suggest that the EPP may have caused an oscillation in the thermosphere, forming the Es_c usually seen in the daytime. Therefore, this study shows the different mechanisms acting together during this magnetic storm, creating a daytime ionosphere after sunset over the SAMA region, as confirmed by observational data and simulations.